ECVHS Geologic Time Scale and Coevolution of Earths Systems Performance Task

Performance TaskRead the scenario below. Complete the performance task by following the directions, making sure to address
all bulleted items.
In the past there have been volcanic eruptions, asteroid impacts, and massive changes to climate which have
impacted life on Earth. Scientists have also discovered that life has changed the atmosphere, oceans and surface
of the Earth in return. What important events occurred in each Period of the geologic time scale that changed
the planet and life on Earth? (For example, the K-T mass extinction at the end of the Cretaceous Period wiped
out many species and set the stage for the appearance of most modern mammal families in the early Tertiary
Period).
You will be responsible for drawing an accurate timeline that explains the coevolution of Earth’s systems and
life on Earth during each era of the geologic time scale. Example timelines can be found on pages 23, 30, 32,
and 33 of this packet.
Your timeline will include:




The 4 eras in the geologic time scale (Precambrian, Paleozoic, Mesozoic, and Cenozoic). These can be
found on page 15 of this packet.
A short description for each era including:
o What Periods of the geologic time scale are part of this era?
o An estimated date in millions of years (Ma) of when this geologic era began and ended.
o A short description of what’s happening to the Earth during this era (examples: continents
shifting, surface features, atmosphere composition, ocean composition).
o A short description of the types of plants and animals that inhabited Earth during this era
(examples: what organisms appeared, what organisms went extinct).
A colored visual for each era.
Citations from resources.
The website below gives step by step instructions for creating a timeline.
http://www.wikihow.com/Make-a-Timeline
wikiHow. “How to Make a Timeline.” WikiHow, WikiHow, 10 Aug. 2017
40
General Science 1A
Credit 1
1
General Science 1A
Credit 1
NAME:____________________
Rev. 5/5/21
WELCOME TO GENERAL SCIENCE IA
Understanding a Unique Earth
This course will introduce you to processes that continue to
make Earth a unique planet that supports life as we know it.
You will learn about the history and formation of Earth,
plate tectonics, Earth’s internal processes, our solar system,
and the universe. You will use the knowledge you have
gained in the course to analyze data, form an opinion, and
defend your opinions based on scientific evidence.
Course at a Glance
Credit
Title
Focus
1A
History of
Earth
Students will understand that life on our planet is a complex process
that has coevolved with Earth’s systems over billions of years. They
will examine the different stages of geologic time to construct a
timeline of Earth’s formation and history.
2A
Modeling
Plate
Tectonics
Students will understand how Earth’s internal processes cycle matter
by thermal convection, and be able to model the layers of Earth’s
interior. They will explain how plate tectonics and continental drift
affect Earth’s surface and ocean floor features.
3A
Earth’s
Internal
Processes
4A
Dating the
Geosphere
5A
Stars and the
Universe
Students will understand that Earth’s internal processes shape Earth’s
surface features. They will relate the process of plate tectonics and
Earth’s internal processes to the development of mountains and
volcanoes, and the occurrence of earthquakes.
Students will understand how the past and current movements of
Earth’s crust can be used to explain the age of crustal rocks. They will
be able to evaluate evidence from ancient Earth materials to construct
an account of Earth’s formation and the different ages of Earth’s
crustal layers.
Students will understand that the Big Bang Theory is based on
astronomical evidence. They will describe how stars, over their life
cycles, produce elements. They will explain how nuclear fusion in our
Sun releases energy in the form of radiation.
2
General Science 1A
Credit 1
NAME:____________________
Course Information
Teacher Contact Information
Supervising Teacher –
Science Teacher –
Phone Number –
Phone Number –
E-mail –
E-mail –
Hours Available –
Hours Available –
Tutoring Hours –
Days and Times –
Tutor Names –
Grading Scale
Mark
A
B
C
D
INC
Indicator
Points
Value
100 –
90%
89 –
80%
79 –
70%
69 –
60%
59 –
0%
Performance Task
40
Quiz
Homework
20
40
Total
100
Student Support Icons
Title
Icon
Description
Review
Activity
This provides the students with a reminder that they need to answer questions.
Technology
Guides students through the tasks and assignments that require the use of
technology and manipulatives.
Reading
This icon lets the students know they will be completing a reading activity.
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General Science 1A
Credit 1
NAME:____________________
CREDIT 1A: HISTORY OF EARTH
Learning Goal for this Credit
Communicate scientific information clearly, thoroughly, and accurately.
Lesson
Title
INTRODUCTION
1.1
The Formation of Earth
1.2
The Geologic Time Scale
1.3
The Precambrian and The Paleozoic
Era
1.4
The Mesozoic and Cenozoic Eras
PERFORMANCE TASK
QUIZ
Assignments

 Connect to Video
 Exploration Activity
 Reading and Questions
 Videos (optional)
 Where Did Earth’s Water Come From?
 Review Questions
 Connect to Prior Knowledge
 Exploration Activity
 Reading and Questions
 Videos (optional)
 History in Rocks
 Analysis Questions
 Connect to Prior Knowledge
 Exploration Activity
 Reading and Questions
 Videos (optional)
 Investigating Paleozoic Fossils
 Review Questions
 Connect to Prior Knowledge
 Exploration Activity
 Reading and Questions
 Videos (optional)
 Weighing the Evidence for a Mass Extinction –
On Land
 Review Questions


Credit Materials



Materials
Pen/Pencil
HMH Earth Science
Textbook (optional)
Packet



Technology Needs
Internet
Computer
HMH Online Resources
(optional)
4
General Science 1A
Credit 1
NAME:____________________
CREDIT 1A: INTRODUCTION
Read “Where Did Earth Come From?” and watch the video “The Sun & The Earth: Crash Course Big History
#3” below. Then answer the essential question.
Where Did Earth Come From?
The Big Bang Theory is the current and most widely accepted theory for the expansion of the universe. The
Big Bang Theory states that billions of years ago all of the matter in the universe was compressed into an
extremely small volume. Then, around 14 billion years ago, a sudden event called the big bang sent this matter
and energy outward in all directions. As the universe expanded, some of the matter began to collect together as
it collided. Solar nebulas, which are rotating clouds of gas and dust, began to form. Scientists believe our solar
system formed from one of these solar nebulas around 4.6 billion years ago. Energy from collisions and
increasing gravity caused the center of this solar nebula to get hotter and denser until hydrogen atoms began to
fuse together. This fusion is what marked the birth of our sun, and is what powers it today. As the sun formed
in the center of the solar nebula, planets began to form as well. Because of the sun’s gravity, the rocky planets
Mercury, Venus, Earth, and Mars formed closer to the sun, and the gas giants Jupiter, Saturn, Uranus, and
Neptune formed further away. As these rocky planets formed, the heavier elements sank to the center forming
layers. As the heavier elements sank toward the core of Earth, the lighter elements began to form a layer that
started cooling to form a crust. Early Earth was very hot and molten, containing no solid rock. This crust
formed the solid rock of Earth’s surface. This solid Earth was still very different from what we see today. It
took billions of years of volcanic activity, impacts from meteors and comets, and a newly forming atmosphere
to make conditions perfect for life to form on Earth.
An essential question is something that allows you to explore the content of the credit. Before you answer the
question watch the video. Then answer the essential question to the best of your ability. You will revisit it at
the end of the credit to see if your answer has evolved.
Video: The Sun & The Earth: Crash Course Big History #3 (14:32)

“The Sun & The Earth: Crash Course Big History #3.” YouTube. CrashCourse, 2 Oct. 2014. Web. 13 May 2015.
Essential Question
Hypothesize on what you imagine Earth looked like before life began. What surface features might you see?
__________________________________________________________________________________________
__________________________________________________________________________________________
__________________________________________________________________________________________
__________________________________________________________________________________________
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General Science 1A
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LESSON 1.1: THE FORMATION OF EARTH
Learning Goal for this Credit
Communicate scientific information clearly, thoroughly, and accurately.
Learning Goals for this Lesson
 Explain the nebular hypothesis of the origin of the solar system.
 Describe how planets form.
 Describe the formation of the land, the atmosphere, and the oceans of Earth.
Lesson Assignments
 Connect to Essential Question
 Exploration Activity
 Reading and Questions
 Videos (optional)
 Where Did Earth’s Water Come From?
 Review Questions
Engage
Connect to Essential Question
What objects make up Earth’s solar system?
__________________________________________________________________________________________
__________________________________________________________________________________________
__________________________________________________________________________________________
__________________________________________________________________________________________
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General Science 1A
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Explore
Exploration Activity
As Earth’s surface formed and the crust slowly cooled into solid masses, there would have been many frequent
volcanic eruptions. These eruptions would have spewed out gases, such as sulfur dioxide (SO2), making the
atmosphere different than the one we know today. Examine the two pictures below. Use them to answer the
following questions. Use the key to the right of the picture to identify the gases.
Chemical
Symbol
Chemical
Name
NH3
Ammonia
H2 O
Water
N2
CO2
Nitrogen
gas
Carbon
Dioxide
Ar
Argon
SO2
Sulfur
Dioxide
CH4
Methane
O2
Oxygen
gas
1. What gases existed in early Earth’s atmosphere that still exist today?
NH3 CH4 SO2
_______________________________________________________________________________________
_______________________________________________________________________________________
2. Which gases exist today, but were absent from early Earth’s atmosphere?
Ar Co2 H2 N2
_______________________________________________________________________________________
_______________________________________________________________________________________
3. What are some differences between the land formations you see in the two pictures? What effects could
these have on the differences in the atmospheres?
O2 H2O
_______________________________________________________________________________________
_______________________________________________________________________________________
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General Science 1A
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Explain
As you complete the reading, answer the questions in the space provided.
Reading
How Did the Solar System Form?
The solar system consists
of the sun, planets, dwarf
planets, and other bodies.
All of these bodies orbit
the sun. Planets are the
main bodies that orbit the
sun. Scientists have
debated the origins of the
solar system for a long
time. Many scientists
once thought that the sun
formed first, and then
threw off the materials
that became the planets.
In 1796, a mathematician
named Pierre-Simon,
marquis de Laplace, had
another idea. His idea is
now called the nebular
hypothesis. Most
scientists today think the nebular hypothesis is the best description of how the solar system formed.
Laplace’s nebular hypothesis states that the sun and the planets formed at about the same time. They formed out
of a rotating cloud of gas and dust called a nebula. The nebula from which our sun and planets formed is called
the solar nebula. About 5 billion years ago, the strength of gravity near the solar nebula increased. This
probably occurred because of a nearby supernova or other forces.
Energy from collisions and pressure from gravity made the center of the solar nebula hotter and denser. When
the temperature at the nebula center became high enough, hydrogen fusion began. The star that we call the sun
formed. About 99% of all the matter that was in the solar nebula now makes up the sun.
1. What is the relationship between the solar nebula and the solar system?
_______________________________________________________________________________________
_______________________________________________________________________________________
The huge cloud of gas and dust in space prior to the formation of our solar system is known as the solar nebula. The solar neb
_______________________________________________________________________________________
8
General Science 1A
Credit 1
How Did the Planets Form?
While the sun was forming at the center of the solar nebula, planets were forming in the outer parts of the
nebula. During the early stages of planet formation, only small bodies called planetesimals existed. Some
planetesimals joined together, forming larger bodies called protoplanets. The gravitational pull of the
protoplanets attracted other planetesimals. These planetesimals collided with the protoplanets, and the masses
combined. Eventually, the protoplanets became very large and formed the planets and moons. The features of a
newly formed planet depended on the distance between the protoplanet and the sun. The protoplanets that
became Mercury, Venus, Earth, and Mars were close to the sun. These planets are small, so they did not have
enough gravitational pull to hold onto some of their gases. Other lighter elements may have been blown or
boiled away by the sun. As the denser material sank to the planet centers, layers formed. Today the inner
planets have solid surfaces. They are smaller, denser, and rockier than the outer planets.
Four other protoplanets became Jupiter, Saturn, Uranus, and Neptune. These planets formed in the cold, outer
regions of the nebula. They did not lose their lighter elements, such as helium and hydrogen. They also kept
ices, such as water, methane, and ammonia ice. At first, thick ice layers surrounded small cores of heavy
elements. Intense heat and pressure in the interiors made the ices melt and form layers of liquid and gas. Today,
the outer planets are called gas giants because they are large and are made up mostly of gases. Uranus and
Neptune are also sometimes called ice giants. Gas giants have low density, and are larger than the inner planets.
Pluto was once known as the ninth planet, but scientists now classify Pluto as a dwarf planet. Like a planet, a
dwarf planet is a spherical body. Unlike a planet, a dwarf planet has not cleared other objects from the path of
its orbit.
How Did Solid Earth Form?
When Earth first formed, it was very hot. Three sources of energy contributed to the high temperatures:
 Energy was produced when the planetesimals that formed the planets collided with each other.
 The increasing weight of the outer layers compressed the inner layers, which generated energy.
 Radioactive materials were very abundant when Earth formed. These materials give off radiation, which
warms the rock around them.
Earth’s center is a dense core composed of heavy elements. A thick layer of rock called the mantle surrounds
the core. The outer layer is a thin crust of rock. These layers formed through a process called differentiation.
During differentiation, dense materials sink and less dense materials rise, forming layers. Eventually, Earth’s
surface cooled enough for solid rock to form. Earth’s surface continued to change as a result of heat in Earth’s
interior. The surface also changed because of impacts and through interactions with the newly forming
atmosphere.
2. How did Earth’s layers develop?
_______________________________________________________________________________________
_______________________________________________________________________________________
During the early phases of Earth’s formation, layers were created through a complicated process called differentiation. Gravity
_______________________________________________________________________________________
How Did Earth’s Atmosphere Form?
Like solid Earth, Earth’s atmosphere formed through the process of differentiation. Earth’s early atmosphere
was made up mostly of hydrogen and helium. The sun heated the gases, allowing them to escape Earth’s
9
General Science 1A
Credit 1
gravity. The solar wind probably blew away the gases. As Earth’s surface continued to form, volcanic eruptions
occurred much more frequently than they do today. The eruptions released large amounts of gases, such as
water vapor, carbon dioxide, nitrogen, methane, sulfur dioxide, and ammonia. This process, known as
outgassing, formed a new atmosphere. Solar radiation caused the ammonia and some of the water vapor in the
atmosphere to break down. Some of the oxygen released during the breakdown formed ozone. The ozone
collected high in Earth’s atmosphere and blocked some ultraviolet radiation, which is harmful to living things.
Organisms that could survive in Earth’s early atmosphere developed. Some of these organisms, such as
cyanobacteria and green plants, used carbon dioxide for photosynthesis. This process released oxygen. Over
time, the amount of oxygen in the atmosphere increased. About 2 billion years ago, the percentage of oxygen in
the atmosphere increased rapidly. It has not changed very much since then.
3. How did the process of outgassing help shape Earth’s atmosphere?
_______________________________________________________________________________________
_______________________________________________________________________________________
The process of outgassing was crucial in the development of Earth’s atmosphere. Volcanic activity was much more common th
_______________________________________________________________________________________
How Did Earth’s Oceans Form?
Some scientists think part of Earth’s water came from space. Icy bodies, such as comets, collided with Earth.
Water from these bodies became part of Earth’s atmosphere. As Earth cooled, water vapor condensed to form
rain. The rain collected on Earth’s surface to form the first oceans. The first oceans were probably made of
fresh water. Over millions of years, rainwater fell to Earth. The water dissolved many solids and carried them to
the oceans. As water evaporated from the oceans, some chemicals combined to form salts. This process made
the oceans more and more salty. Carbon dioxide from the atmosphere dissolves in the oceans. When carbon
dioxide levels in the atmosphere decrease, more heat can escape into space. Over Earth’s history, the
concentration of carbon dioxide in the atmosphere has increased and decreased periodically. As a result, Earth
has had climates that were warmer and cooler than today’s climate.
4. How do scientists think Earth’s oceans formed?
The formation of the oceans on Earth is thought to have involved a number of events occurring over a very long
_______________________________________________________________________________________
period of time. It’s possible that comets or other frozen bodies impacted with the young Earth and contributed some
of the planet’s water. These encounters caused the atmospheric water vapor to be released. This water vapor
_______________________________________________________________________________________
condensed into rain when Earth cooled, slowly building up on the planet’s surface to form the first oceans. There’s a
_______________________________________________________________________________________
good chance that fresh water made up these early oceans. Furthermore, carbon dioxide from the atmosphere
dispersed into the oceans, affecting the dynamics of the planet’s climate. Throughout Earth’s history, variations in
5.
In this section,
have
learned
theclimatic
formation
of Earth’s
land,
atmosphere,
oceans.
Which
atmospheric
carbon you
dioxide
levels
haveabout
caused
changes
that have
resulted
in periodsand
of both
warmer
and
components
of Earth’s
composition
it capable
of supporting
life? rains. The seas’
colder
climates.Water
built upcurrent
on the Earth’s
surfacemake
over millions
of years
due to persistent
Due
to a number
of crucialby
factors,
the makeup
of the
Earth
today
particularly
well suited
for oceans.
supporting
composition
was affected
the dissolved
minerals
and
solids
thatisthis
water brought
into the
Thelife:
oceans’
_______________________________________________________________________________________
Moderate
climate
and atmosphere:
nitrogen,
two gases
that are
for water
life asdrained
we know
it on
saltiness grew
throughout
time as aOxygen
result ofand
specific
chemicals
combining
to necessary
form salts as
from
them.
Earth,
are
among
the
gases
that
make
up
the
atmosphere.
Additionally,
the
atmosphere
maintains
a
steady
climate
_______________________________________________________________________________________
that shields the Earth from dangerous radiation and drastic temperature changes. Carbon dioxide and other
_______________________________________________________________________________________
greenhouse gases help to maintain the planet’s temperature and make it suitable for life. Earth is the only planet
that
is A.,
known
to have
lot ofofliquid
water
on its surface.
Water
as a Holt
habitat
for aEarth
variety
of Interactive
creatures
and Holt
as a
Allison,
Mead
et al. “Chapter
27:aPlanets
the Solar
System/Section
1: Formation
of theserves
Solar System.”
McDougal
Science
Reader,
solvent
for biological
making
it anCo.,
essential
component of life as we know it. Oceans and Continents: The
McDougal,
a Division
of Houghtonactivities,
Mifflin Harcourt
Publishing
2010, pp. 407–412.
existence of both oceans and continents offers a variety of habitats for different sorts of life. A wide variety of marine
organisms are supported by oceans, whereas terrestrial plants, animals, and ecosystems can be found on land.
Cycles of Nutrients: The recycling of nutrients and upkeep of a stable environment are fundamental functions of
Earth’s dynamic geology and interrelated systems, such as the nitrogen and carbon cycles. This makes it possible for
intricate ecosystems to survive. Ozone Layer: The ozone layer protects life on Earth from dangerous ultraviolet
rays. It is created when oxygen molecules interact with ultraviolet light in the upper atmosphere. Organisms can live
at the surface thanks to this barrier layer. Biodiversity: Due to the lengthy evolutionary history of Earth and its
10
diverse ecosystems, a vast range of species have developed that are suited to distinct niches. Magnetic Field:
General
1Acosmic radiation, which otherwise could degrade
Earth’s magnetic field protects against dangerous
solar Science
wind and
the atmosphere and impede the formation and sustenance
Credit 1of life. Biodiversity contributes to ecological resilience and
the interrelated web of life.Together, these elements produce a distinct and well-balanced ecosystem that fosters the
intricate interactions of various life forms, making Earth a habitable planet.
Videos
If you would like to learn more about this topic, watch the videos below for more information. (Optional)
Solar System 101 (4:10)

Where is Earth in our solar system? Where are the rest of the planets located?
In this interactive virtual investigation, you will get to explore our universe and see how
gravity played a role in forming it.
“Solar System 101 | National Geographic” YouTube. National Geographic, 30 Aug 2017. Web. 26 Apr 2021.
How Was Planet Earth Formed? (3:27)

How did the Earth develop into the rocky planet that we know today? This video will
explain how the different layers of the Earth formed.
“Less Than Five – How Was Planet Earth Formed?” YouTube. Astronimate, 20 Dec 2016. Web. 26 Apr 2021.
Why Is There Air? (4:34)

“Why Is There Air?” YouTube. DNews, 27 June 2014. Web. 14 May 2015.
Why is there air? This video will discuss where Earth’s atmosphere came from and why it is
different from the atmospheres of other planets in our solar system.
Where Did Earth’s Water Come From? (2:59)

“Where Did Earth’s Water Come From?” YouTube. MinuteEarth, 7 Feb. 2014. Web. 18 Sept. 2014.
Was Earth’s water delivered from comets and meteor impacts? Watch this video
for evidence regarding this hypothesis about the origin of Earth’s water.
11
General Science 1A
Credit 1
Elaborate
Where Did Earth’s Water Come From?
Water has some unique properties and is essential for life on Earth. But where did Earth’s water come from? In
the following excerpts from two articles, you will read about evidence for different hypotheses regarding the
origins of Earth’s water. As you read the information, answer the questions that accompany them.
In trying to understand the formation of the early Earth, some researchers have suggested that the planet was
dry and inhospitable to life until icy comets pelted the earth and deposited water on the surface.
Wendy Panero, associate professor of earth sciences at Ohio State, and doctoral student Jeff Pigott are
pursuing a different hypothesis: that Earth was formed with entire oceans of water in its interior, and has
been continuously supplying water to the surface via plate tectonics ever since.
Researchers have long accepted that the mantle contains some water, but how much water is a mystery. And,
if some geological mechanism has been supplying water to the surface all this time, wouldn’t the mantle have
run out of water by now?
Because there’s no way to directly study deep mantle rocks, Panero and Pigott are probing the question with
high-pressure physics experiments and computer calculations.
“When we look into the origins of water on Earth, what we’re really asking is, why are we so different than
all the other planets?” Panero said. “In this solar system, Earth is unique because we have liquid water on
the surface. We’re also the only planet with active plate tectonics. Maybe this water in the mantle is key to
plate tectonics, and that’s part of what makes Earth habitable.”
Gorder, Pam F. “Study Hints That Ancient Earth Made Its Own Water—Geologically.” The Ohio State University News Room. Ohio State University, 17 Dec. 2014.
Web. 25 Feb. 2015.
Water molecules were surely part of the dusty swirl that coalesced into the Sun and its planets beginning
about nine billion years after the Big Bang. But Earth’s early history, including epochs with high ambient
temperatures and no enveloping atmosphere, implies that surface water would have evaporated and drifted
back into space. The water we encounter today, it seems, must have been delivered long after Earth formed.
Faced with this conundrum, astronomers realized that there are two ready-made sources: comets and
asteroids, the solar system’s gravel strewn among planetary boulders. The primary difference between the
two is that comets typically have a greater concentration of ingredients that vaporize when heated,
accounting for their iconic gaseous tails. Both comets and asteroids can contain ice. And if, by colliding with
Earth, they added the amount of material some scientists suspect, such bodies could easily have delivered
oceans’ worth of water. Accordingly, each has been fingered as a suspect in the mystery.
Greene, Brian. “How Did Water Come to Earth?” Smithsonian.com. Smithsonian Magazine, May 2013. Web. 25 Feb. 2015.
12
General Science 1A
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1. According to the first article, where did Earth’s water come from? What evidence does this article give
to support this?
In
the
article, it is stated that some scientists, such as Wendy Panero and Jeff Pigott, put forth the theory that Earth
_______________________________________________________________________________________
started with enormous seas of water in its interior, and that this water has been continuously delivered to the surface
by plate tectonics. Through high-pressure physics tests and computer simulations, the researchers are attempting to
_______________________________________________________________________________________
determine whether there is water present in the Earth’s mantle. According to the report, this water in the mantle may
_______________________________________________________________________________________
be what gives Earth its unique properties of having liquid water on its surface and active plate tectonics. This theory
stresses the possibility of an ongoing internal water supply through geological processes and refutes the notion that
2.
toonly
the came
second
article,
where did Earth’s water come from? What evidence does this article
the According
Earth’s water
from
ice comets
give to support this?
According to the article, comets and asteroids that hit Earth after it formed are the most plausible sources of the
_______________________________________________________________________________________
planet’s water. Surface water would have evaporated under early Earth circumstances, but comets and asteroids
carrying water-rich ice might have brought large volumes of water to the planet. As pre-existing sources of water,
_______________________________________________________________________________________
these heavenly planets’ collisions with Earth may have aided in the development of the oceans. The article
_______________________________________________________________________________________
emphasizes that comets and asteroids can both include ice, and that these objects’ encounters with Earth may be
what caused water to exist on the planet despite its difficult early history.
3. After reading both articles, where do you think Earth’s water came from? Use evidence from the
articles to support your reasoning.
I_______________________________________________________________________________________
am inclined to lean toward the hypothesis that Earth’s water mostly came from icy comets and asteroids colliding
with the planet after its initial formation in light of the facts provided in the articles. In the articles, it is explained how
the early Earth’s high temperatures and lack of an atmosphere would have likely caused any surface water to
_______________________________________________________________________________________
evaporate and escape into space. It seems possible that comets and asteroids carried water-rich ice that, when
_______________________________________________________________________________________
colliding with Earth, delivered a sizable amount of water to the planet’s surface. Both comets and asteroids have the
capacity to contain water, according to the papers, while comets have a larger concentration of volatile substances
that can vaporize, giving them their recognizable tails. While the second article offers the idea that Earth gets its
water from outside sources such as comets and asteroids, the evidence for these sources is more consistent with the
difficulties Earth’s early environment had with keeping surface water. It’s crucial to remember that scientific
knowledge is susceptible to change as more research is done, and additional information could help to clarify the real
source of Earth’s water.
Evaluate
Review Questions
Answer the following questions.
1. Explain the nebular hypothesis.
A generally recognized scientific theory explaining how our solar system came to be is the nebular hypothesis. This
_______________________________________________________________________________________
theory postulates that the “solar nebula,” a huge cloud of gas and dust, is where the solar system first formed. A
disruption, such as a nearby supernova explosion, caused the solar nebula to start collapsing under the force of its
_______________________________________________________________________________________
own gravity. The nebula started to spin and flatten into a whirling disk as it shrank. The majority of the material built
_______________________________________________________________________________________
up in the Sun’s center, while the leftover gas and dust in the disk started to condense via a process known as
accretion. These collections of objects, called planetesimals, collided and combined to become protoplanets.
2. Describe how our solar system developed.
The nebular theory states that our solar system evolved through a number of phases. The collapse of the solar
_______________________________________________________________________________________
nebula led to the development of the Sun in the core, with leftover material in the surrounding disk forming
planetesimals and protoplanets. Mercury, Venus, Earth, and Mars are examples of inner planets that are also
_______________________________________________________________________________________
referred to as terrestrial planets. These planets originated closer to the Sun, where it was hotter, leading to the
_______________________________________________________________________________________
evaporation of lighter elements and the prevalence of stony materials. The outer planets, or gas giants (Jupiter,
Saturn, Uranus, and Neptune), however, originated in a colder, farther-from-the-Sun environment. This made it
3.
Whyfor
arethe
thesolar
outer
planetsouter
more
gaseous
thanmore
the inner
planets?
possible
nebula’s
regions
to hold
ices and
volatile gases, which led to the buildup of these
Because
of the
in temperature
and gaseous
composition
in the environments
where they
evolved,
substances
andvariations
the formation
of the massive
atmospheres
that characterize
the gas
giantsthe outer planets
_______________________________________________________________________________________
are more gaseous than the inner planets. Due to the lower temperatures, gases like hydrogen and helium, as well as
other volatile chemicals, were able to condense into solid ice solids in the solar nebula’s outer regions. These volatile
_______________________________________________________________________________________
substances were more abundant as the outer planets gathered material from this area, giving origin to their
_______________________________________________________________________________________
considerable gaseous atmospheres. The inner planets, on the other hand, developed in a hotter environment nearer
to the Sun, where lighter gases were forced to flee and stony, metallic materials were left behind. As a result, the
outer planets have much thicker and more massive atmospheres that are dominated by hydrogen, helium, and other
gases, whereas the inner planets have relatively thin or no atmospheres made largely of heavy elements
13
General Science 1A
Credit 1
LESSON 1.2: THE GEOLOGIC TIME SCALE
Learning Goal for this Credit
Communicate scientific information clearly, thoroughly, and accurately.
Learning Goals for this Lesson
 Summarize how scientists worked together to develop the geologic column.
 List the major divisions of geologic time.
Lesson Assignments
 Connect to Prior Knowledge
 Exploration Activity
 Reading and Questions
 Videos (optional)
 History in Rocks
 Analysis Questions
Engage
Connect to Prior Knowledge
What are some ways that we measure time?
__________________________________________________________________________________________
__________________________________________________________________________________________
Both in daily life and in scientific contexts, time is measured using a variety of techniques and units. Here are some typical method
__________________________________________________________________________________________
__________________________________________________________________________________________
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General Science 1A
Credit 1
Explore
Exploration Activity
The geologic time scale represents the chronological order of Earth’s history. It is organized by major events
and changes that have occurred. These events are based on fossil and geological records. The geologic time
scale is divided by a series of units based on where specific rocks or fossils are found. The three basic units of
time include eras, periods, and epochs. Each is measured in millions of years (Ma). Examine the following
geologic time scale. Then answer the questions below.
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General Science 1A
Credit 1
1. What are the different eras in the geologic time scale?
The geologic time scale gets divided into several eras. Based on that, each of them encompas a significant period of
_______________________________________________________________________________________
Earth’s history:
Precambrian Era
Paleozoic Era
Mesozoic Era
Cenozoic Era
_______________________________________________________________________________________
_______________________________________________________________________________________
2. Approximately how many millions of years did each last?
Precambrian Era: Over 4 billion years Paleozoic Era: Around 291 million years Mesozoic Era: Approximately 186
_______________________________________________________________________________________
million years
Cenozoic Era: About 66 million years and ongoing
_______________________________________________________________________________________
_______________________________________________________________________________________
3. When did oceans first appear?
round 4 billion years ago, during the Early Precambrian Period, it is thought that the first oceans began to form.
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
4. During which period did the atmosphere reach its current oxygen rich state?
Specifically during the Proterozoic and Phanerozoic eras of the Paleozoic Era, the atmosphere achieved its current
_______________________________________________________________________________________
oxygen-rich condition.
_______________________________________________________________________________________
_______________________________________________________________________________________
5. During which period did land organisms appear? How many millions of years ago did this take place?
Around 541 million years ago, during the Cambrian epoch of the Paleozoic Era, the first land creatures evolved.
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
6. During which period did the first primates appear? During which period did humans appear?
Around 66 million years ago, during the Paleogene stage of the Cenozoic Era, the first primates emerged. Humans
_______________________________________________________________________________________
(genus Homo) first appeared considerably later, around 2.8 million years ago, during the Quaternary epoch of the
Cenozoic Era.
_______________________________________________________________________________________
_______________________________________________________________________________________
16
General Science 1A
Credit 1
Explain
As you complete the reading, answer the questions in the space provided.
Reading
What Is a Geologic Column?
Earth’s surface is always changing. The layers of rock in Earth’s crust record these changes. Scientists study
these rock layers to learn about Earth’s history. No one area on Earth has a complete record of Earth’s history.
Therefore, scientists from around the world share what they learn from the rock record. These scientists
developed a standard order of rock layers called a geologic column. The oldest rocks are at the bottom of the
column. The more recent rocks are at the top of the column. In a geologic column, different layers hold
different types of rock and fossils. Fossils in the upper layers look like modern plants and animals. Many fossils
in the lower, older layers are from extinct plants and animals. Scientists can use geologic columns to estimate
the ages of rock layers. Scientists compare a layer of rock with a similar layer in a geologic column. The layers
they compare may be in the same position relative to other layers. They may have the same fossils. If the two
rock layers match, they probably formed around the same time.
1. Where on a geologic column would you most likely find fossils of extinct organisms? Explain your
answer.
The bottom strata of a geologic column are where fossils of extinct creatures are most likely to be discovered. This is
_______________________________________________________________________________________
due to the fact that a geologic column has a set hierarchy, with the oldest rocks at the bottom and the most recent
rocks at the top. fossilized remains of ancient plants and animals can be found in the bottom levels because they are
_______________________________________________________________________________________
older. As you climb the column, you come across more recent rock strata that contain fossils of creatures that lived
_______________________________________________________________________________________
more recently than those that do now.
2. How can scientists use a geologic column to determine a rock layer’s age?
By comparing a rock layer to the known order of layers in a geologic column, scientists may utilize the column to
_______________________________________________________________________________________
establish the age of the rock layer. Similar rock types, fossils, and other traits among layers suggest that they likely
developed at the same period. These characteristics enable scientists to infer the age of a rock layer from its position
_______________________________________________________________________________________
in the column in relation to layers whose ages are known. This aids in creating a time line for the history of Earth and
_______________________________________________________________________________________
the development of life.
What Are the Divisions of Geologic Time?
Scientists use what they have learned from rocks and fossils to create a geologic time scale. The geologic time
scale identifies major events in Earth’s past. It also summarizes changes in Earth’s surface, climate, and
organisms over time. Scientists use these changes to divide the geologic time scale into smaller units. Fossils
from certain organisms characterize each unit of geologic time.
The largest unit of geologic time is an eon. Geologic time has four eons, as shown on page 15. The first three
eons are part of Precambrian time. Precambrian time lasted 4 billion years. It makes up most of Earth’s
history. After Precambrian time, the Phanerozoic Eon began. Eons are divided into shorter units of time called
eras. Eras are divided into shorter units of time called periods. Each period has specific types of fossils.
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General Science 1A
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Periods are usually named for the place where the fossils were first found. For example, the Jurassic Period is
named for the Jura Mountains in Europe. Sometimes periods are divided into shorter units called epochs.
Scientists make this division only if there is enough information from the fossil record. Epochs can be divided
into even shorter units called ages. Scientists need a detailed fossil record to mark ages.
3. List the following units of time from shortest to longest: age, eon, epoch, era, period, year.
Age Epoch Period Era Eon
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
4. What is needed by scientists to divide an epoch into ages?
A thorough fossil record is required for scientists to split an era into ages. The numerous animals and creatures that
_______________________________________________________________________________________
lived throughout that time are described in this record. Scientists may designate particular ages based on the
changes in the fossil record and distinguish various periods within an era by examining the fossils and their features.
_______________________________________________________________________________________
This procedure necessitates a thorough knowledge of the fossilized remnants present in the Earth’s geological strata.
_______________________________________________________________________________________
Allison, Mead A., et al. “Chapter 9: A View of Earth’s Past/Section 1: Geologic Time.” Holt McDougal Earth Science Interactive Reader, Holt McDougal, a Division
of Houghton Mifflin Harcourt Publishing Co., 2010, pp. 123–126.
Videos
If you would like to learn more about this topic, watch the videos below for more information. (Optional)
Four Ways To Understand the Earth’s Age (3:44)

Sneideman, Joshua M. “Four Ways to Understand the Earth’s Age – Joshua M. Sneideman.” YouTube. TED-Ed, 29 Aug. 2013.
Web. 12 Sept. 2014.
How old is the Earth? In this video the age of the Earth is compared to one calendar
year to show how extremely old Earth is compared to us humans.
Crash Course Big History: The Evolutionary Epic
(14:33)

“Crash Course Big History: The Evolutionary Epic | Big History Project.” YouTube. Big History Project, 5 Sept. 2014. Web.
19 Sept. 2014.
What did life look like during the different periods of the geologic time scale? This
video explores the different periods of the geologic time scale.
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General Science 1A
Credit 1
Elaborate
History in the Rocks
Geologists have learned a lot about the geologic history of Earth. They have studied the arrangement of rock
layers. They have also studied the arrangement of fossils in the rock layers. Fossils give clues about the
environment in which the organism that made the fossil lived. Scientists can also find the ages of the fossilbearing rocks in which fossils are found because the ages of many fossils have been found through radiometric
dating of associated igneous rocks. Radiometric dating, fossil age, and rock arrangement are all used to tell what
changes have happened in the arrangement of the rock layers through geologic time. In this lab, you will
discover how the geologic history of an area can be told by studying the arrangement of fossils and rock layers.
Directions:
Study the fossils shown in Figure A. Note their placement in related groups and the geologic periods in which
the organism that made the fossil lived. Select one of the four rock columns shown in Figure B. This figure
shows how some of these fossils may happen in a series of rock layers. Record the number of the column you
are using __________.
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General Science 1A
Credit 1
Using Figures A and B on the previous page, answer the following questions.
1. List the fossil names from your column in order from bottom to top.
Trilobite Cephalopod GastropodP elecypod
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
2. Do the fossils in your column appear in the order of geologic time?
The fossils do not appear in the order of geologic time
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
3. Do the fossils in your column appear in order of geologic periods? If not, which periods are missing?
The fossils appear in order of geologic periods
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
Evaluate
Analysis Questions
Answer the following questions.
1. What might have happened that would explain the order in which fossils were found in each of the rock
columns? (Hint: What can happen to rock layers that could cause them to appear out of order?)
The order of fossils in rock columns can be explained by various geological processes that affect rock layers over
_______________________________________________________________________________________
time. Tectonic pressures can deform or move rock layers, causing them to appear out of their original order. This
phenomena is known as “folding” or “faulting,” and it is rather common. In addition, activities like erosion can expose
_______________________________________________________________________________________
older rock layers beneath the surface. The arrangement of rock layers and the subsequent order of fossils can shift
_______________________________________________________________________________________
as a result of volcanic activity and sedimentary deposition.
2. Study column 3 in Figure B. Note that there is a rock layer that has no fossils between two rock layers
that have fossils. Hypothesize on how this might have happened?
The lack of fossils in the rock layer between two fossil-bearing strata in column 3 of Figure B may be due to a
_______________________________________________________________________________________
“unconformity,” a void in the sedimentary record. When there is a period of erosion or non-deposition, in which strata
are either eroded or not created, unconformities occur. This might occur as a result of shifting environmental factors
_______________________________________________________________________________________
like sea level changes or a protracted period of no sediment deposition, which prevents the buildup of sediment
_______________________________________________________________________________________
containing fossils
3. Describe what the area you live in might have been like when the organisms in your chosen column
lived.
The
environment in my neighborhood could have been very different from what it is today based on the time period it
_______________________________________________________________________________________
belongs to. Since the area corresponds to the Paleogene period of the Cenozoic Era, the region might have included
the earliest mammals and a shifting climate as Earth moved from a world dominated by dinosaurs.
_______________________________________________________________________________________
_______________________________________________________________________________________
Mead, Allison, et al. “Skills Practice Lab: History in the Rocks.” Holt McDougal Online, Holt McDougal, a Division of Houghton Mifflin Harcourt Publishing Co,
2010, my.hrw.com/sh2/es10/teacher/osp/hqx/data/chap09/section01/dscl_a.pdf.
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General Science 1A
Credit 1
LESSON 1.3: THE PRECAMBRIAN AND THE
PALEOZOIC ERA
Learning Goal for this Credit
Communicate scientific information clearly, thoroughly, and accurately.
Learning Goals for this Lesson
 Summarize how evolution is related to geologic change.
 Identify the major biological and geological events of Precambrian time.
 Identify the major biological and geological events of the Paleozoic Era.
 List the periods of the Paleozoic Era.
Lesson Assignments
 Connect to Prior Knowledge
 Exploration Activity
 Reading and Questions
 Videos (optional)
 Investigating Paleozoic Fossils
 Review Questions
Engage
Connect to Prior Knowledge
How could physical changes to Earth, such as an ice age or rising sea levels, lead to physical changes in
organisms?
Natural selection, a process, can cause physical changes in organisms as a result of physical changes in the
environment brought on by physical changes to the Earth, such as ice ages or rising sea levels. Here is how creatures
__________________________________________________________________________________________
may be impacted by these changes:
Ice Ages and Cooling Periods: Cold Environment Adaptations Organisms may
have to adjust to cooler conditions during ice ages or cooling periods. This can entail growing larger bodies to retain heat,
__________________________________________________________________________________________
thickening their hair or feathers, or adapting behaviours that enable them to endure colder climates.
Changes in
Habitat and Range: Habitats may alter when ice sheets grow and sea levels fall. As an organism’s past habitats become
__________________________________________________________________________________________
uninhabitable, it may be necessary for it to migrate or adapt to a new environment. In order to better adapt to the new
__________________________________________________________________________________________
circumstances, this could result in changes in behaviour, food, and physical traits. Rising Sea Levels: Habitat Loss and
Migration: Coastal habitats may get inundated as a result of rising sea levels. To avoid getting flooded, organisms may
need to move to higher ground or find other homes. Changes in behaviour, reproduction, and interactions with other
species could result from this.
Adaptations to Aquatic Environments: Increasing aquatic environments may be a
result of rising sea levels. Organisms might develop adaptations to survive in these novel environments, such as
specialised swimming structures or the ability to gather food from underwater sources. Altered Food Chains:
Environmental Changes can disrupt food chains and availability. Changes in Food Availability. When prey populations
change, organisms may need to adapt their diets, feeding habits, or hunting techniques.
Changes in available food
sources may be responsible for the evolution of specialised feeding structures or behaviours to take use of new food
sources. Resistance to Environmental Stressors: Organisms may develop defence systems to deal with environmental21
GeneralFor
Science
1A they might become tolerant of the increasing
stressors brought on by shifting environmental conditions.
instance,
Credit
1
saline in the water brought on by rising sea levels or adjust to temperature changes. Competition and the Forces of
Evolution: Interspecies Competition The competitive environment among animals can change as habitats change.
Organisms may confront greater competition for resources or encounters with new predators, leading to the evolution of
features that provide a competitive advantage.
Explore
Exploration Activity
The timeline of the Earth above lists the relative geologic eras to scale. During the Precambrian between 4
billion and 3.8 billion years ago the early Earth began to cool which allowed water vapor to condense and fall as
rain. Once liquid water was present, organic compounds could be formed from inorganic compounds. There
are multiple hypotheses on how these organic molecules formed, and how the first living cells arose, but once
life was present on Earth it began to transform the planet. Some of the most common fossils of Precambrian
time are cyanobacteria. Cyanobacteria are unicellular (single celled) organisms that are photosynthetic. They
take in carbon dioxide gas and release oxygen gas into the atmosphere similar to modern day plants.
Answer the questions below.
1. How old is the Earth?
It is approximately 4.6 billion years old.
_______________________________________________________________________________________
_______________________________________________________________________________________
2. Did unicellular or multicellular life appear first? How do you know?
Life with only one cell initially appeared. The paragraph identifies cyanobacteria, which are unicellular creatures, as
_______________________________________________________________________________________
some of the most prevalent Precambrian remains. This implies that single-celled life existed before multicellular
existence
_______________________________________________________________________________________
3. What are cyanobacteria?
Cyanobacteria are photosynthetic, unicellular organisms. Through the process of photosynthesis, they are able to
_______________________________________________________________________________________
use sunlight to transform carbon dioxide and water into glucose and oxygen. Cyanobacteria were instrumental in the
early Earth’s history because they helped the atmosphere become more oxygenated by releasing oxygen gas as a
_______________________________________________________________________________________
byproduct of photosynthesis.
4. How did cyanobacteria contribute to the evolution of multicellular organisms like the plants and animals
we see today?
Oxygen
gas released into the atmosphere by cyanobacteria played a crucial role in altering the Earth’s environment.
_______________________________________________________________________________________
The Great Oxygenation Event, also referred to as the Oxygen Catastrophe, took place about 2.4 billion years ago.
The evolution of multicellular life forms like plants and animals that use oxygen for respiration was facilitated by the
_______________________________________________________________________________________
increase in atmospheric oxygen, which allowed for the development of more sophisticated, aerobic creatures. The
conditions that eventually enabled the emergence and diversity of the complex life forms we see today were
indirectly influenced by cyanobacteria in this way
General Science 1A
Credit 1
22
Explain
As you complete the reading, answer the questions in the space provided.
Reading
What Is Evolution?
Earth’s history is recorded in rock layers. The fossils from each layer show which species of organisms existed
when the layer formed. Scientists study and compare fossils from different times in Earth’s history. By
studying fossils, scientists have discovered evidence that species have changed over time. Scientists use the
term evolution to describe this change. Evolution is the process in which new species develop from existing
species. Scientists find evidence for evolution when they compare fossils to living organisms.
Geologic and climatic changes affect the ability of many organisms to survive. Scientists use evidence from
rocks and fossils to find out how environmental changes affected organisms in the past. The fossil record
shows that some species survived environmental changes but that some species disappeared. Scientists study
fossils to find out why some species changed over time and why some stayed almost the same. They also try to
find out why species became extinct.
1. What is evolution?
New species form over a very long time from existing species through a process called evolution. It involves slow,
_______________________________________________________________________________________
cumulative genetic changes in populations over generations that result in the emergence of novel features,
morphologies, and eventually, unique species.
_______________________________________________________________________________________
_______________________________________________________________________________________
2. How do geologic changes affect evolution?
The physical environment in which organisms live can be changed by geologic processes, which can have a
_______________________________________________________________________________________
substantial impact on evolution. Climate changes, the creation of new landforms, variations in sea level, volcanic
activity, and other phenomena are among these changes. Geologic alterations may result in the creation of new
_______________________________________________________________________________________
habitats, the isolation of populations, or the destruction of existing habitats, resulting in a variety of selective
_______________________________________________________________________________________
pressures that affect the survival and procreation of numerous creatures. It is more likely for species to survive and
pass on their favourable qualities to the following generation if they are better suited to their changing environment.
These adaptations can build up over time, possibly resulting in the extinction of certain species and the creation of
Whyother
Do Scientists
Know
Little
Precambrian Time?
ones that are
more Relatively
adapted to the
newAbout
environment.
Most scientists agree that Earth formed about 4.6 billion years ago. Earth formed as part of a cloud of dust, or
nebula. Over time, particles from the cloud formed Earth and other planets. The formation of Earth was the
beginning of Precambrian time. Precambrian time lasted about 4 billion years and makes up about 88% of
Earth’s history. Scientists do not know much about what happened during Precambrian time. Geologic changes
have deformed the rock layers from the time. The layers are not in their original order. Thus, the rock record is
hard to interpret, or understand.
23
General Science 1A
Credit 1
Earth has many areas of exposed, or uncovered, Precambrian rocks. These areas are called shields. Precambrian
shields result from millions of years of geologic changes. Precambrian rocks have very few fossils.
Precambrian organisms did not have hard parts such as bones or shells that fossilize easily. Precambrian rocks
are also very old. Volcanic eruptions, erosion, and movement of tectonic plates probably destroyed most
Precambrian fossils. Scientists have discovered a few Precambrian fossils. The most common fossils are
cyanobacteria. These fossils are found in stromatolites, or reef-like deposits that form in water. Scientists have
also discovered Precambrian fossils of marine worms and jellyfish.
3. What are two characteristics of Precambrian rocks?
The following are two characteristics of Precambrian rocks:
They don’t have many fossils: Because the species
_______________________________________________________________________________________
of the Precambrian period lacked hard features that might easily fossilize, such bones or shells, Precambrian rocks
include extremely few fossils.
They’re really old: Some of the Earth’s earliest rocks come from the Precambrian
_______________________________________________________________________________________
period, which dates back billions of years to the planet’s early genesis
_______________________________________________________________________________________
4. Why do scientists not divide Precambrian time into smaller units based on the fossil record?
The lack of fossils in Precambrian rocks makes it challenging to build a precise and consistent timeline of biological
_______________________________________________________________________________________
history, which is why scientists do not split Precambrian time into smaller units based on the fossil record. The
inability to distinguish between different species and trace evolutionary changes over time is a result of the scarcity of
_______________________________________________________________________________________
well-preserved fossils from this time period. Furthermore, it’s possible that many of the fossils that were originally
_______________________________________________________________________________________
present have been lost or altered by the immense geologic processes that have taken place over billions of years,
including volcanic activity, erosion, and tectonic movements. As a result, it has been difficult to establish the kind of
precise divides that are achievable for more recent times in Earth’s history due to the scarcity of fossils and the
What
Changes
Happened
the Paleozoic
Era? record
difficulties
associated
within
interpreting
the geological
The Paleozoic Era began 542 million years ago and ended 251 million years ago. When the Paleozoic Era
began, many small continents were scattered over Earth. By the end of the Paleozoic Era, the smaller continents
had moved and collided, or crashed into each other. This movement formed the supercontinent Pangaea. The
collisions lifted large areas of land and formed mountain ranges. Paleozoic rocks have many fossils. These
fossils show that the number of plant and animal species increased during the Paleozoic Era. Scientists have
used the detailed fossil record to divide the Paleozoic Era into six periods: Cambrian, Ordovician, Silurian,
Devonian, Carboniferous, and Permian.
Many marine, or sea, organisms appeared during the Cambrian Period. The warm, shallow waters on Earth
were perfect for marine invertebrates, or animals without backbones. The most common Cambrian
invertebrates were trilobites. Scientists use many kinds of trilobite fossils as index fossils. Cambrian
invertebrates also included brachiopods, a kind of animal with a shell. Many kinds of brachiopods lived during
this period, but very few exist today. Worms, jellyfish, snails, and sponges also existed during the Cambrian
Period.
During the Ordovician Period, brachiopods and other marine organisms, such as graptolites, became more
common. At the same time, the number of trilobite species decreased. By this period, vertebrates had appeared.
Vertebrates are animals with backbones. The earliest vertebrates were fish. Fish in the Ordovician Period did
not have jaws or teeth. Their bodies had thick, bony plates.
Vertebrate and invertebrate marine life thrived during the Silurian Period. Corals and relatives of modern sea
stars became more common. Eurypterids, shown below, also lived during this period. Near the end of the
Silurian Period, early land plants and animals evolved.
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General Science 1A
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The Devonian Period is called the Age of Fishes. Rocks from this period hold fossils of many bony fish. One
group of fishes, lungfish, could breathe air. Another group of fishes, rhipidistians, may have used their strong
fins to crawl on land. Early amphibians, such as the ancestors of modern frogs, probably evolved from
rhipidistians. Land plants, such as ferns, also appeared during this period.
During the Carboniferous Period, Earth’s climate was generally warm. Humidity was often very high. Forests
and swamps covered much of the land. Over many millions of years, these forests and swamps became coal
deposits. These coal deposits exist today in places such as Pennsylvania and Ohio. In North America, scientists
divide the Carboniferous Period into the Mississippian Period and the Pennsylvanian Period. Amphibians and
fish thrived during the Carboniferous Period. Crinoids were common ocean animals. Insects such as giant
cockroaches and dragonflies were common land animals. Near the end of the period, early reptiles, which
looked like large lizards, appeared.
The Permian Period is the last period in the Paleozoic Era. Many environmental changes happened during this
period. By the start of the Permian Period, the continents had joined to form Pangaea. New mountain ranges
formed, and areas of dry land developed. The warm, shallow seas became smaller. The environmental changes
caused a mass extinction of Paleozoic organisms. In a mass extinction, a very large number of species becomes
extinct at about the same time. As the seas became smaller, there were fewer habitats for marine species. During
the mass extinction at the end of the Permian Period, most marine invertebrates, such as trilobites, died out.
However, fossils show that many reptiles and amphibians survived the changes. Animals from these groups
dominated Earth for millions of years after the Paleozoic Era.
5. How did Pangea form?
Tectonic plate movement caused Pangaea to develop. At first, during the Paleozoic Era, the landmasses of Earth
_______________________________________________________________________________________
were dispersed all over the place. The movement of the tectonic plates over millions of years caused the smaller
continents to progressively shift and crash with one another. These collisions and motions caused the landmasses to
_______________________________________________________________________________________
gradually come together to form the supercontinent known as Pangaea
_______________________________________________________________________________________
6. What may have caused the explosion of life during the Cambrian Period?
It is believed that a number of reasons contributed to the “Cambrian Explosion,” which is the term used to describe
_______________________________________________________________________________________
the proliferation of life during the Cambrian Period. The existence of new biological niches as a result of
environmental changes on Earth, such as increased atmospheric oxygen concentrations and the emergence of more
_______________________________________________________________________________________
complex marine ecosystems, was probably a significant role. Additionally, the quick diversification of life forms might
_______________________________________________________________________________________
have been aided by genetic advancements and the accumulation of genetic variation over time. Scientists are still
debating the precise cause of the Cambrian Explosion, but it was a critical time for evolutionary innovation and the
appearance of a wide variety of complex multicellular animals in the fossil record
Allison, Mead A., et al. “Chapter 9: A View of Earth’s Past/Section 2: Precambrian Time and the Paleozoic Era.” Holt McDougal Earth Science Interactive Reader,
Holt McDougal, a Division of Houghton Mifflin Harcourt Publishing Co., 2010, pp. 127-132.
25
General Science 1A
Credit 1
Videos
If you would like to learn more about this topic, watch the videos below for more information. (Optional)
The Grand Canyon: Evidence of Earth’s Past (2:51)
http://www.pbslearningmedia.org/resource/ess05.sci.ess.earthsys.nautiloid/the-grandcanyon-evidence-of-earths-past/
WGBH. “The Grand Canyon: Evidence of Earth’s Past.” PBS LearningMedia. NOVA, 2006. Web. 19 May 2015.
How can scientists study the Precambrian and Paleozoic Era? In this video you will see
how the Grand Canyon gives a glimpse into the past with rock layers that are up to 1.7
billion years old.
Cambrian Explosion (13:07)
http://www.pbslearningmedia.org/resource/11dae54b-299a-4b45-a964d574e8dc3320/cambrian-explosion/
“Cambrian Explosion.” PBS LearningMedia. Shape of Life, 2014. Web. 19 May 2015.
What was the Cambrian explosion? This video focuses on fossilized organisms found in
the Burgess Shale formation of the Canadian Rockies. It discusses their evolution and
sudden arrival during the beginning of the Paleozoic Era.
NOVA scienceNOW: Mass Extinction (4:50)
http://www.pbslearningmedia.org/resource/oer09.sci.life.evo.massextinct/mass-extinction/
WGBH. “NOVA ScienceNOW: Mass Extinction.” PBS LearningMedia. NOVA, 2009. Web. 19 May 2015.
What could have caused the mass extinction during the Permian Period at the
end of the Paleozoic Era? This video will explore the evidence for different
hypotheses to discover what may have caused this mass extinction.
26
General Science 1A
Credit 1
Elaborate
Investigating Paleozoic Fossils
Background:
Unlike Precambrian rocks, Paleozoic rocks hold vast amounts of fossils. Plant and animal life flourished and
evolved into many different species during the Paleozoic Era. Many species that we see present today evolved
from ancestral species that were present during the Paleozoic Era. This rich fossil record has given scientists an
insight into what life may have looked like between 250 million to 500 million years ago.
Examine the following fossils and compare them to some present day organisms. Use your observations to
answer the questions.
During the early Paleozoic Era organisms called
trilobites flourished in the warm, shallow seas. They
went extinct toward the end of the Permian period.
During the mid-Paleozoic Era organisms called
eurypterids lived in shallow lagoons. Eurypterids
had one pair of legs for swimming and four or five
pairs of legs for walking.
Horseshoe crabs like the one in this picture are alive
in the oceans today. They can be found in warm
shallow ocean waters with soft sandy or muddy
bottoms.
Different species of scorpions, like the one in this
picture, are found throughout the world. They are
characterized by their 4 pairs of legs, a pair of
pinchers, and a curved tail ending with a venomous
stinger.
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Toward the end of the Paleozoic Era organisms
called crinoids were common in the oceans. They
were marine animals that attached to rocks or the
ocean bottom.
These sea lilies are marine animals that inhabit the
Earth’s oceans today. They attach to rocks on the
sea floor with a stalk. They feed by filtering
particles with their tentacle-like arms.
Analysis:
1. Compare the trilobite fossil and the horseshoe crab. What do you notice that is similar about them?
What do you notice that is different?
Similarities
Both trilobites and horseshoe crabs have segmented exoskeletons that offer support and protection.
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Additionally, they both have an arthropod body type with a long, segmented tail and a unique head area. Both were
likely sea animals and had jointed appendages. Trilobites are extinct, although horseshoe crabs are still alive
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today. In comparison to trilobites, horseshoe crabs have a larger, more prominent carapace and a lengthy tail spine
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that is utilised for stability and steering.
2. Compare the eurypterid fossil and the scorpion. What do you notice that is similar about them? What
do you notice that is different?
Similarities: Eurypterids and scorpions both have hard exoskeletons and jointed legs, making them arthropods. They
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each have unique heads, segmented bodies, and long, tail-like structures, giving them comparable body forms. Both
are thought to have existed as predators in aquatic settings. Differences: Eurypterids, sometimes known as sea
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scorpions, are extinct marine arthropods that lived primarily in the water, in contrast to scorpions, which are primarily
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terrestrial in nature. While eurypterids presumably have various adaptations for life in water, scorpions have a stinger
at the end of their tails for defence and prey capture.
3. Compare the crinoid and the sea lilies. What do you notice that is similar about them? What do you
notice that is different?
Sea lilies and crinoids are both marine echinoderms that are distinguished by a cup-shaped body structure linked to
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a stalk or stem. Each of them has a pair of feathery arms that they utilise to filter feed and collect food particles from
the water. Differences: Some species of crinoids are referred to as “sea lilies” in the common language. Their
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distinct morphologies and preferred habitats, as well as probable variations in arm configurations and body sizes,
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may be the primary differences between them
4. Develop a hypothesis to explain why you think eurypterids developed legs even though they lived on the
ocean floor.
Despite
living on the ocean floor, eurypterids had legs, possibly to help them move around and across the substrate.
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It’s possible that these legs were modified for scavenging, hunting, or looking for prey in the silt. Natural selection
may have gradually favoured eurypterids with more mobile legs, giving them a competitive edge in locating food,
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evading predators, and entering various watery habitats. They may have been able to explore a greater variety of
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ecological niches as a result of this adaptation, which may have aided in their survival and evolutionary progress
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Evaluate
Review Questions
Use the diagram below to answer the following questions.
1. During which period did the first vertebrates appear? Estimate the date in millions of years (Ma).
Around 488 million years ago (Ma), during the Ordovician Period, the earliest vertebrates are thought to have first
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evolved
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2. During which period did land plants appear? Estimate the date in millions of years (Ma).
The origin of land plants is also thought to have occurred during the Ordovician Period, some 443 million years ago
_______________________________________________________________________________________
(Ma).
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3. During which period did the first animals appear on land? What type of organisms were they? Estimate
the date in millions of years (Ma).
Arthropods, notably terrestrial arthropods like the earliest insects, are possibly the first animals to have evolved on
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land. Around 443 million years ago (Ma), during the Silurian Period, this transition most likely took place
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4. During which period did the supercontinent Pangea form? Estimate the date in millions of years (Ma).
Around 335 million years ago (Ma), during the Late Carboniferous and Early Permian Periods, the supercontinent
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Pangaea started to develop.
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LESSON 1.4: THE MESOZOIC AND CENOZOIC
ERAS
Learning Goal for this Credit
Communicate scientific information clearly, thoroughly, and accurately.
Learning Goals for this Lesson
 List the periods of the Mesozoic and Cenozoic Eras.
 Identify the major biological and geological events of the Mesozoic Era.
 Identify the major biological and geological events of the Cenozoic Era.
Lesson Assignments
 Connect to Prior Knowledge
 Exploration Activity
 Reading and Questions
 Videos (optional)
 Weighing the Evidence for a Mass Extinction – On Land
 Review Questions
Engage
Connect to Prior Knowledge
Hypothesize on a possible way that the mass extinction at the end of the Mesozoic Era contributed to mammals
becoming the dominant life-forms during the Cenozoic Era.
By eliminating competition and filling ecological niches left vacant by the demise of numerous non-avian dinosaurs and
other species, it’s probable that the mass extinction at the end of the Mesozoic Era helped mammals become the
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dominant life forms during the Cenozoic Era.The mass extinction event, which is frequently linked to the collision of a
huge asteroid or comet, caused significant ecological destruction and the extinction of numerous species, including the
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dominating reptile groups. Food networks and ecosystems would have been significantly disrupted as a result of this
catastrophic catastrophe, providing possibilities for creatures that survived to adapt and take advantage of new
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niches.Mammals, which were smaller and more biologically diverse than bigger reptilian animals throughout the
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Mesozoic, may have been less impacted by the extinction catastrophe. Mammals could have quickly diversified to fill the
empty ecological roles as the dominating reptile populations declined. Mammals who had previously inhabited nocturnal
or tiny niches might have taken advantage of the chance to broaden their range and adapt to new settings.Additionally,
because there were fewer species in the post-extinction environment, mammals may have been able to fill niches that
were previously filled by dinosaurs and other reptiles. A favorable environment for mammalian radiation and
diversification may have been created by the decreased competition.It’s also possible that the extinction event changed
the climate, vegetation patterns, and food resources, which would have favored some mammalian lineages’ capacity for
adaptation. Mammals that possessed characteristics that were useful for utilizing novel food sources or surviving in novel
settings may have prospered and evolved quickly.
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Explore
Exploration Activity
The Mesozoic Era began after the Permian mass extinction that happened at the end of the Paleozoic Era. Even
though a mass extinction of a large number of life occurred, fossils indicate that reptiles and amphibians were
able to survive the environmental changes that killed off so many other species. The Mesozoic Era is also
known as the Age of Reptiles because of the success of these reptiles and amphibians. Use the timeline above to
answer the following questions.
1. During which Period did the supercontinent Pangea begin to break apart? Estimate the date in millions
of years (Ma).
Around 200 million years ago (Ma), during the Jurassic Period, the supercontinent Pangea started to disintegrate.
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2. During which Period did mammals first appear? Estimate the date in millions of years (Ma).
Triassic Period, which is thought to have occurred roughly 225 million years ago (Ma), is when mammals first
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emerged.
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3. During which period did the first primitive birds appear? Estimate the date in millions of years (Ma).
Around 150 million years ago (Ma), during the Jurassic Period, the earliest known birds began to fly.
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4. During which period did the first modern birds appear? Estimate the date in millions of years (Ma).
Neornithes, the ancestors of modern birds, first appeared during the Cretaceous Period, some 85 million years ago
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(Ma)
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5. About how many millions of years ago (Ma) did dinosaurs become extinct?
At the conclusion of the Cretaceous Period, around 66 million years ago (Ma), dinosaurs went extinct, drawing a line
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between the Mesozoic and Cenozoic eras
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The Cenozoic Era began after the Cretaceous-Tertiary mass extinction at the end of the Mesozoic Era.
Dramatic climate changes occurred as continental ice sheets spread across nearly one-third of Earth’s land.
New species that were better adapted to life in cooler climates appeared. Mammals became the dominant lifeform. Because of their success, the Cenozoic Era is known as the Age of Mammals. The Cenozoic Era
continues on today into the present. Use the timeline above to answer the following questions.
6. By what Epoch had most modern mammal families appeared? Estimate the date in millions of years
(Ma).
By
the
Oligocene Epoch, which is thought to have occurred about 34 million years ago (Ma), the majority of extant
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mammal families had emerged.
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7. During what Epoch did the first hominids appear? Estimate the date in millions of years (Ma).
According to estimates, the first hominids emerged during the Miocene Epoch roughly 23 million years ago (Ma).
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8. During what Period and what Epoch did modern humans appear? Estimate the date in millions of years
(Ma).
According
to estimates, between 300,000 and 200,000 years ago (Ma), modern humans (Homo sapiens) first
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appeared during the Quaternary Period, specifically in the Late Pleistocene Epoch.
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Explain
As you complete the reading, answer the questions in the space provided.
Reading
What Changes Happened During the Mesozoic Era?
During a mass extinction, large numbers of species become extinct around the same time. At the end of the
Permian Period, more than 70% of land organisms and 90% of marine organisms became extinct. The Mesozoic
Era followed this mass extinction. The mass extinction left space and resources for the species that survived.
During the Mesozoic Era, many new species evolved.
During the Mesozoic Era, Pangaea broke into smaller continents. Shallow seas and marshes covered much of
the land. In general, the climate was warm and humid. The conditions were good for reptiles. Lizards, turtles,
crocodiles, snakes, and many dinosaurs thrived during the Mesozoic Era. This era is often called the Age of
Reptiles. The Mesozoic Era left a rich fossil record. Based on the fossil record, scientists divide the Mesozoic
Era into three periods: Triassic, Jurassic, and Cretaceous.
Many dinosaur species lived during the Triassic Period. Some dinosaurs were the size of squirrels. Others were
nearly 30 m long. Most dinosaurs were about 2 m to 5 m long and moved quickly. Reptiles called ichthyosaurs
lived in the oceans during the Triassic Period. New marine invertebrates evolved, such as the ammonite. On
land, small mammals appeared in the forests.
Dinosaurs became the dominant organism during the Jurassic Period. Fossil records show that two major
groups of dinosaurs evolved. Scientists distinguish the dinosaurs in these groups by their hip bones. The
Jurassic Period also had flying reptiles, such as the pterosaur. The pterosaur flew on skin-covered wings, like
modern bats do. Jurassic rocks also show evidence of early birds, such as Archaeopteryx.
Dinosaurs continued to dominate Earth during the Cretaceous Period. Tyrannosaurus rex was almost 6 m tall,
which made it one of the largest carnivores from this time. Its sharp teeth were up to 15 cm long. The armored
ankylosaurs and the horned ceratopsians were other dinosaurs of the Cretaceous Period. Flowering plants, or
angiosperms, evolved during this period. Angiosperms include magnolia and willow trees. Later, trees such as
maples, oaks, and walnuts became common. Angiosperms are the dominant type of land plant today.
The Cretaceous Period ended in a mass extinction that included the dinosaurs. Some scientists think that
changes such as volcanoes and continental shifts caused the extinction. However, many scientists use the impact
hypothesis to explain the mass extinction. According to the impact hypothesis, an asteroid crashed into Earth
65 million years ago. The crash threw dust into the air. The dust blocked the sun and caused Earth’s climate to
cool. Many species could not survive the cooler climate. Over time, the dust settled over Earth and formed a
layer of sediment. This sediment was full of the element iridium. Iridium is common in asteroids, but
uncommon in rocks on Earth.
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1. What is one major geologic development during the Mesozoic Era?
he division of the supercontinent Pangaea into smaller continents was one of the main geologic changes that
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occurred during the Mesozoic Era.
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_______________________________________________________________________________________
2. What do many scientists think caused the mass extinction of the dinosaurs?
Many scientists believe that an asteroid impact was what led to the catastrophic extinction of dinosaurs at the end of
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the Cretaceous Period. According to this impact theory, an asteroid collided with Earth, causing major climatic
changes and a cooling of the climate that had an impact on ecosystems all over the world.
_______________________________________________________________________________________
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3. How could you identify the boundary between the Cretaceous and Tertiary Periods in a rock sample?
Explain your answer.
The presence of the unique layer known as the Cretaceous-Paleogene (K-Pg) boundary in a rock sample can
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frequently be used to determine the boundary between the Cretaceous and Tertiary Periods, which was defined by
the mass extinction event. Iridium, an element that is uncommon in Earth’s rocks but prevalent in asteroids, is highly
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concentrated in this layer, which gives it its distinctive properties. The catastrophe that caused the extinction of the
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dinosaurs and the start of the Tertiary Period is clearly marked by this iridium-rich stratum
What Changes Happened During the Cenozoic Era?
The Cenozoic Era began 65 million years ago after the mass extinction at the end of the Mesozoic Era. Earth
had many climate changes during the Cenozoic Era. At times, ice sheets covered almost one-third of Earth’s
land. New species that could survive in cool climates appeared. Mammals became the dominant organisms.
Thus, the Cenozoic Era is called the Age of Mammals. The Cenozoic Era is divided into two periods: the
Tertiary and the Quaternary. These periods are divided into seven epochs: the Paleocene, Eocene, Oligocene,
Miocene, Pliocene, Pleistocene, and Holocene.
During the Paleocene Epoch, many new mammal species evolved. The first primates also evolved during this
time. The tarsier is a modern primate with ancestors from the Paleocene Epoch.
During the Eocene Epoch, the first horses, whales, flying squirrels, and bats appeared. Small reptiles continued
to thrive. At the end of the Eocene Epoch, Earth’s climate cooled further.
During the Oligocene Epoch, continents collided and formed the Himalayas in Asia. Earth’s climate became
cooler and drier. Many early mammals became extinct. However, large species of deer, pigs, horses, camels,
cats, and dogs survived. Marine invertebrates, such as clams and snails, continued to thrive. Grasses and
hardwood trees flourished in this climate.
The Miocene Epoch had changes in currents and sea levels. The largest known land mammals existed during
this epoch. Miocene rocks contain fossils of horses, camels, deer, rhinoceroses, pigs, raccoons, wolves, and
foxes. They also contain fossils of saber-toothed cats, which are now extinct.
During the Pliocene Epoch, predators such as bears, dogs, and cats evolved into their modern forms. Modern
horses also appeared. Near the end of the Pliocene, climate changes caused the ice sheets to grow. As more
water froze, sea levels fell. A land bridge appeared between Eurasia and North America. Changes in Earth’s
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crust formed a land bridge between North and South America. Organisms moved between the continents on
these land bridges.
During the Pleistocene Epoch, ice sheets changed in size many times. Some animals, such as the woolly
mammoth, had thick fur that helped them survive the cold climate. Other species survived by moving to warmer
areas. Some species became extinct. Pleistocene rocks have fossils of early modern humans. Cave paintings
suggest that early humans may have been hunters.
The Holocene Epoch began about 11,500 years ago as the last glacial period ended. The Holocene continues
today. As the ice sheets melted, sea levels rose. Coastlines took on their present shapes. In the early Holocene
Epoch, modern humans began to farm and use tools made of bronze and iron.
4. What do the start of the Mesozoic Era and the start of the Cenozoic Era have in common?
The beginning of the Mesozoic and Cenozoic eras both came after significant mass extinction events, which is one
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thing they share in common. After the great extinction that occurred at the end of the Permian Period, the Mesozoic
Era started, and the Cenozoic Era followed the mass extinction that occurred at the conclusion of the Mesozoic Era
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_______________________________________________________________________________________
5. What is one major geologic development during the Cenozoic Era?
The emergence of massive ice sheets and glaciations, which resulted in dramatic climatic changes and the rise and
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retreat of ice sheets across the surface of the Earth, is one major geologic development during the Cenozoic Era
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Allison, Mead A., et al. “Chapter 9: A View of Earth’s Past/Section 3: The Mesozoic and Cenozoic Eras.” Holt McDougal Earth Science Interactive Reader, Holt
McDougal, a Division of Houghton Mifflin Harcourt Publishing Co., 2010, pp. 133-138.
Videos
If you would like to learn more about this topic, watch the videos below for more information. (Optional)
Dinosaur Supremacy – Walking With Dinosaurs – BBC (3:59)

“Dinosaur Supremacy – Walking With Dinosaurs – BBC.” YouTube. BBC Earth, 4 Aug. 2012. Web. 26 Sept. 2014.
What allowed dinosaurs to begin appearing during the Triassic Period? This video will
show how a combination of speed and agility gave early dinosaurs an evolutionary edge.
The Smell of Prey – Walking with Dinosaurs in HQ – BBC (2:48)

“The Smell of Prey – Walking with Dinosaurs in HQ – BBC.” YouTube. BBC Earth, 9 Nov. 2012. Web. 26 Sept. 2014.
What top predatory dinosaurs had evolved by the Jurassic Period? This video will show
how dinosaur species had evolved to become top predators, but also had evolved
defenses against predators.
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Reptiles of the Skies – Walking with Dinosaurs in HQ – BBC (4:31)

“Reptiles of the Skies – Walking with Dinosaurs in HQ – BBC.” YouTube. BBC Earth, 9 Nov. 2012. Web. 26 Sept. 2014.
How did dinosaurs conquer the skies during the Cretaceous Period? This video will
show how some dinosaur species evolved special adaptations for flight.
Microraptor – Flying Dinosaur – Planet Dinosaur – BBC (4:00)

“Microraptor – Flying Dinosaur – Planet Dinosaur – BBC.” YouTube. BBC Earth, 24 May 2013. Web. 26 Sept. 2014.
How did feathers begin evolving in dinosaurs? This video will show how primitive
feathers were used for gliding from tree to tree.
Asteroid attack 1 – an answer? – What Really Killed the Dinosaurs?
– BBC (3:08)

“Asteroid Attack 1 – an Answer? – What Really Killed the Dinosaurs? – BBC.” YouTube. BBC Earth, 24 Aug. 2011. Web. 26 Sept.
2014.
What caused the mass extinction at the end of the Cretaceous Period? This video will
investigate the K-T boundary to try and discover what caused this mass extinction.
Age of Mammals – Global Processes (3:11)

“Age of Mammals – Global Processes.” YouTube. NHMLA, 9 Aug. 2010. Web. 29 Sept. 2014.
How has the Earth changed over the past 65 million years? This video will show continents
moved, climate changed, and mammals evolved.
Primeval Kill – BBC (4:04)
https://www.youtube.com/watch?v=saplHLrMC0&list=PL22E84F0E32D9C37D&index=5
“Primeval Kill – BBC.” YouTube. BBC Worldwide, 19 Oct. 2007. Web. 30 Sept. 2014.
How do scientist think predators like sabretooth cats hunted during the Pleistocene Epoch?
This video will explore what life was like during this time.
The Last of the Mammoths | Natural History…