1
Unit 4:
Earth Through Time
Lesson 1: The Age of Earth’s Rocks
Lesson 2: Earth’s History
Name: ___________________
Teacher: ____________PD:___
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Unit 4: Lesson 1 Vocabulary
1
Sediment:
2
Fossils:
3
Relative Age:
4 Absolute Age:
5
Index Fossil:
6
Half-Life
7 Fossil Record:
8 Unconformity:
3
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Lesson 1: The Age of Earth’s Rocks
The Wentletrap, an invertebrate with a spiral shell,
existed during the Paleozoic Era. These organisms
are part of the Gastropod group of animals that
successfully lived in fresh water, in ocean habitats,
and on land
Glossopteris, a fern-like plant, existed between 200300 million years ago and evidence suggest it had
lived on multiple continents throughout Earths’
history.
Brachiopods, which existed and thrived during the
Paleozoic Era, were marine animals that resembled
clams. Brachiopods were one of many species that
became almost entirely extinct at the end of the
Paleozoic Era.
Crinoids, which are often called sea-lilies, resembled
flowers, but are actually considered animals and are
related to sea urchins, starfishes, and brittle stars.
They thrived on Earth roughly 500 million years ago.
Earth’s History
Earth's history is not divided into evenly-spaced segments. It is divided
based on major changes and events. For example, a segment of time
called the Paleozoic Era ranges from 543 to 251 million years ago. This era
is defined by two major events: an increase in the diversity of plants and
animals at the beginning and a mass extinction at the end. In this unit, you
will investigate methods of determining ages of rocks and fossils, and the
types of evidence that scientists use to organize Earth's history.
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WHY IT MATTERS!
Here are some questions to consider as you work through the unit.
Can you answer any of the questions now? Revisit these questions at
the end of the unit to apply what you discover.
Questions:
Why might you want to study the
geologic history of a certain area?
What can you learn?
What tools and resources can you
use to learn about the geologic
history of an area?
How can you use the concepts of
relative dating and absolute
dating to learn about the geologic
history of an area?
How might you use information
from the rock and fossil records to
infer what the environment of an
area was like in the past?
How might you infer what an area
was like at a certain time period in
Earth's history if no fossils are
found in that area?
Notes:
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Unit Starter: Sequencing Events
Each item on this timeline is an event from a portion of Earth’s History
Decoding the Timeline
Circle the correct answer for each statement:
1. This timeline spans more than three / four hundred million
years
2. The earliest known dinosaurs appeared on Earth before /
after the earliest known reptiles appeared. Dinosaurs became
extinct about 45 / 65 million years ago, which was before /
after the earliest known birds appeared.
3. When thinking about Earth’s history, it is important to
remember that events that occurred millions of years ago
occurred before / after events that took place thousands of
years ago.
Lesson 1: The Age of Earth’s Rocks
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The colorful rock layers that make up these hills in Oregon contain clues about the history of the area.
Can You Explain It?
How could the ages of these dinosaurs be determined?
v
History of Dinosaur Provincial Park
77 - 75 million years ago
These dinosaurs lived alongside turtles,
crocodiles, and small mammals. The
area consisted of swamps and lush
vegetation, as well as many rivers that
flowed into a nearby sea.
75 - 72 million years ago
The nearby sea rose slowly for a few
million years until it completely covered
the area. This sea was full of creatures
including sharks and the animals shown
in the drawing.
Present Day
Over the last 72 million years, this area
and its plants and animals changed many
times. This is a photo of the area today,
now known as Dinosaur Provincial Park.
The park is in Alberta, Canada.
The rocks and fossils found today in Dinosaur Provincial Park tell us about the park's past environments,
plants, and animals. How do you think the ages of the animals shown above were determined?
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Sedimentary Rock Formation and Fossils
Sedimentary rocks are made of tiny rock pieces called sediment. Some sedimentary rocks are
made from the remains of plants and animals. For example, limestone can be made of the
remains of microscopic organisms. Sedimentary rock can form when erosion moves
sediment to low-lying areas such as valleys and lake bottoms. The sediment settles in layers
and becomes compressed as lower layers are buried under the weight of upper layers. Water
containing dissolved substances seeps through the sediment layers. The substances come
out of the solution and harden, acting as a glue to form rock.
As sedimentary layers form, they stack up one by one. If undisturbed by Earth processes,
sedimentary rocks stay in horizontal layers. The oldest layer is at the bottom and the
youngest layer is at the top.
Over very long periods, bodies of water can dry up. As the
water evaporates, dissolved substances in the water
become solids. This can form sedimentary rock.
Over time, shells and sediment pile up at the bottom of
lakes and oceans. These pieces can form rocks, such
as coquina.
Fossils in Sedimentary Rock
When a plant or animal dies, it often decomposes or is eaten by animals. However, if it is
quickly buried by sediment, evidence of the organism can be preserved. The sediment
hardens and becomes a rock, which contains a fossil. Fossils are the traces or remains of
an organism that lived long ago.
Fossils are most commonly preserved in
sedimentary rock. Some fossils look like
parts of an organism, but are not the
organism’s actual parts. Bone, shell, or
wood, for example, can be replaced by
minerals that form a rock version of the
part. Fossils can also show traces of an
animal’s activity, such as footprints or
burrows. Not all fossils are preserved in
rock. Ice, tar, and tree sap can contain
fossils as well.
Analyzing Fossils
Under certain conditions, dead organisms can be preserved as fossils. Write
captions for the second and third photos below to explain how the living starfish
became a fossil.
Different types of
starfish have lived on
Earth for over 400
million years! The
starfish in this photo
lives in the ocean.
Describing Earth’s Past
Label each fossil with the name of the environment in which it likely formed.
Word Bank
A tropical forest
A lake
A grassland
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Absolute vs Relative Age
Relative age is described in terms of whether an object is older or younger
than other objects. Absolute age identifies how old an object is, as
expressed in units of time. In other words, absolute age is the actual age of
something.
Do the Math
The first step in finding a rock’s absolute age is to measure the amounts of unstable
particles and the stable particles they form. Next, the rate at which the unstable particles
break down must be found. This rate of change is called half-life. Half-life is the amount
of time needed for half the amount of unstable particles to change into more stable
particles. The igneous rock shown formed when magma from Earth’s interior traveled to
the surface and cooled. The rock contains unstable particles of uranium that break
down into a more stable form of lead over time. The rate at which the uranium breaks
down is known. It takes 704 million years for half the rock’s uranium to change to lead.
That is, the half-life is 704 million years. At any point in time, the amounts of uranium
and lead can be measured to find the rock’s age.
Half-Lives Passed
0
16
0
Time Passed
(millions of
years)
0
1
8
8
704
2
4
12
1408
3
Unstable Particles Stable Form of the
in the Rock
Particle
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Lab Summary Page
Radioactive Dating
Lab Summary
1. What is a half-life?
2. Does the half-life of an element ever change? Are there any environmental factors
that could affect the half-life of radioactive elements?
__________________
Radioactive Decay Curve
Base your answers to questions 3 through 6 on the
graph which represents the disintegration of a
sample of a radioactive element. At time t = 0 the
sample has a mass of 4.0 kilograms.
3. What is the half-life of the isotope?
A) 1.0 min B) 2.0 min C) 3.0 min
D) 4.0 min
4. What mass of the material remains at 4.0 minutes?
A) 1 kg
B) 2 kg
C) 0 kg
D) 4 kg
5. How long did it take for the mass of the sample to reach 0.25 kilogram?
A) 1 min
B) 5 min
C) 3 min
D) 8 min
6. If the mass of this material had been 8.0 kilograms at time t = 0, its half-life would
have been
A) less
B) greater
C) the same
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Fossils
In most cases, fossils are the same age as the rock in which they are
found. An index fossil is the remains of an organism that was common
and widespread, but only existed for about 1 million years or less. The age
of an index fossil can help establish the ages of rocks and other fossils. For
example, specific ammonite fossils are found in Dinosaur Provincial Park.
They are marine index fossils that are about 75 million years old. The rocks
in which they are found, and any other fossils in those rocks, are also likely
about 75 million years old.
Organizing all of Earth’s known fossils from oldest to youngest shows how
life on Earth has changed over time. All of Earth’s known fossils and the
information they provide is known as the fossil record. The fossil record
grows as fossils are continually discovered.
Concept Review
This type of trilobite is an index fossil that lived
about 440 million years ago. Fossils of the
trilobite and the brittle star were found in the
same rock layer. What can you infer about
these two organisms?
A.
B.
C.
D.
They likely lived at the same time.
They are likely closely related.
They likely lived in different habitats.
They are likely younger than the rock layer.
Unconformity
Some rock layers are missing, forming gaps in the rock record. Such a gap
is called an unconformity. These gaps can occur when rock layers are
eroded or when sediment is not deposited for a period of time. In this way,
rock layers are like pages in a book of Earth’s history—only some pages
were torn out or never written in the first place!
Using Relative Dating & Relative Age
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Determining Relative Age
Relative age is described in terms of whether an object is older or younger
than other objects.
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Lab Summary page
Geologic Sequence Lab
A
B
1. Put the layers in order from oldest to
youngest
______ oldest
______
______ youngest
C
Explain your reasoning
_______________________________
2. Did the fault occur before or after
all three layers were deposited?
Explain your answer with evidence
from the diagram.
_____________________________
_____________________________
_____________________________
_____________________________
3. Which layer is the oldest?
Why?
___________________________
___________________________
4. Which layers are the
youngest? Why?
___________________________
___________________________
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Unit 4 - Lesson 1 Review
How could the ages of these dinosaurs be determined?
v
History of Dinosaur Provincial Park
77 - 75 million years ago
These dinosaurs lived alongside turtles,
crocodiles, and small mammals. The
area consisted of swamps and lush
vegetation, as well as many rivers that
flowed into a nearby sea.
75 - 72 million years ago
The nearby sea rose slowly for a few
million years until it completely covered
the area. This sea was full of creatures
including sharks and the animals shown
in the drawing.
Present Day
Over the last 72 million years, this area
and its plants and animals changed many
times. This is a photo of the area today,
now known as Dinosaur Provincial Park.
The park is in Alberta, Canada.
1. State your claim. Make sure your claim fully explains how the ages of the animals
were determined.
2. Summarize the evidence you have gathered to support your claim and explain
your reasoning.
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Concept Review: Age of Earth’s Rocks
Multiple Choice Review
7. The three cross sections of sedimentary bedrock
Potassium-40, turns into Argon when it decays, and is
shown below represent widely separated surface
found in igneous rocks. It has a half-life of 1.3 billion
exposures of layers that contain fossils. Letters A, B, C,
years. Answer the following questions and explain
and D represent four different marine fossils found in
your thinking.
these rock layers.
1. What is the parent? ______________
2. What is the daughter product? __________________
3. After 1.3 billion years what percentage of Pottasium40 is left?
Which letter best represents an index fossil?
4. After 2.6 billion years what percentage of Pottasium40 is left?
(1) A
(3) C
(2) B
(4) D
8. What is the relative age of a fault that cuts across
many rock layers?
5. After 2.6 billion years what is the percentage of
Argon?
6. The diagram below shows a geologic cross section.
Letters A through D represent different rock units.
(1) The fault is the same age as the top layer it cuts
across.
(2) The fault is the same age as the bottom layer it cuts
across.
(3) The fault is younger than all the layers it cuts across.
(4) The fault is older than all the layers it cuts across.
9. Unless a series of sedimentary rock layers has been
overturned, the bottom rock layer usually
(1) is the oldest
(2) has the finest texture
(3) contains the greatest variety of minerals
(4) contains fossils
10. An unconformity between two sedimentary layers is
most likely produced by
Which sequence correctly shows the age of the lettered
rock units, from oldest to youngest?
A) a period of extrusive vulcanism followed by another
period of extrusive vulcanism
(1) A → B → C → D
B) uplift followed by extensive erosion, submergence,
and deposition
(2) C → D → A → B
(3) D → B → A → C
(4) D → C → B → A
C) continuous sedimentation in a deep basin over a long
period
D) the deposition of gravel followed by the deposition of
sand and silt
Lesson 2: Earth’s History
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This fossil of a tyrannosaur skeleton was found buried in a layer of sandstone, a sedimentary rock.
Can You Explain It?
What evidence is used to construct this timeline of Earth’s History?
There is a growing body of evidence showing that the first known life forms appeared at least 3.5 billion years ago.
Complex life did not evolve until more than a billion years later, the first humans showed up only 200,000 years ago.
Review this geologic timeline of events in Earth’s history. What kinds of evidence
are used to make timelines like this one?
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Rate of Geologic Change
Most geologic processes change Earth‘s surface so slowly that you would not notice a
difference in your lifetime. But over thousands to millions of years, geologic processes
cause major changes to landscapes. The movement of tectonic plates is an example—
they move at a rate of a few centimeters (cm) each year. Yet over millions of years, this
motion builds tall mountain ranges and forms entire ocean basins.
Not all geologic change is slow. Some processes can alter large areas or the whole
planet within a short period. An example is the meteorite that struck the Yucatan
Peninsula in Mexico about 65 million years ago. It sent debris into the atmosphere that
blocked sunlight for years and likely contributed to a mass extinction.
Quick Check
Geologic change is shown in each photo. Read each description, and then label the images to
tell whether you think that the change is relatively fast or slow.
This landslide happened
when rocks and soil
suddenly slid down the side
of this mountain as a result
of the force of gravity.
The Colorado River has
been carving a path through
the Grand Canyon for at
least 5 million years. In some
spots, the canyon is 1,620
meters (m) deep and
continues to get deeper
today.
For millions of years, two
tectonic plates have been
pushing up the Himalayan
Mountains. The mountains
are still growing today at
about 1 centimeter per
year.
Using Rock Layers to Determine the Past
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The rock record is a compilation of all of Earth’s known rocks. Major
geologic events—such as a supervolcano eruption, an asteroid impact, or
tectonic plate movements that form or break up continents—are recorded
in the rock record.
Long ago, a supervolcano eruption happened in Yellowstone National Park,
Wyoming. The cooling ash formed deposits of rock called volcanic tuff of
varying thicknesses all over the United States. Absolute dating indicates
that the tuff is 640,000 years old. The information from all of the known tuff
deposits, along with the rocks above and below it, can be compiled to give
a big picture view of what the United States was like before, during, and
after the eruption.
The rocks in the first row of photos give clues about how they formed. The photos in the
second row show different environments. Match each rock with the type of environment in
which it formed by placing the correct letters in the box.
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Correlating Rock Sequences
A team of geologists sketched these three different undisturbed rock sequences
in a region. They worked together to build this diagram that correlates the fossils
from each sequence.
9. Most of the rocks found were sedimentary, but a few were igneous. Based on
the absolute ages of the igneous rocks, help the scientists describe the relative
ages of the fossils by circling the correct answers below.
Fossils of extinct organisms, such as this Stegosaurus, are generally younger /
older than fossils that resemble living organisms. Assuming that the fossils
formed at the same time as the rocks they are found in, the oyster /
Stegosaurus fossils are the oldest fossils shown here. The igneous layer
indicates that Stegosaurus lived before / after 95 million years ago.
10. Name any plants or animals that existed during the following times:
A. Existed more than 95 million years ago: _____________________
________________________________________________________
B. Existed between 95 and 25 million years ago: ________________
________________________________________________________
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The Geologic Time Scale
Earth has existed for about 4.6 billion years. The geologic time
scale is used to organize Earth’s long history into manageable
parts. The geologic time scale is continually updated as new
rock and fossil evidence is discovered. The further we go back
in time, the less rock and fossil information we have. This is
because Earth’s oldest rocks have undergone great changes
over the past few billion years. Many of the oldest rocks have
either been buried deep below the surface or melted in Earth’s
hot interior.
The Geologic Time Scale
Earth’s entire history is divided into four major eons, shown in the top row of the
diagram. In the second row, the three eras within the Phanerozoic Eon are shown.
Within each era are several periods, and within each period are even smaller divisions
of time called epochs. Currently, we live in the Holocene Epoch of the Quaternary
Period, which is part of the Cenozoic Era and the Phanerozoic Eon.
B
A
D
C
E
F
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A
The Geologic Time Scale
Archean Eon
Over 3 billion years ago,
photosynthetic organisms released
oxygen into Earth’s shallow iron-rich
seas. Scientists think that oxygen
combined with iron to form the red
bands in this rock.
B
Proterozoic Eon
These photosynthetic sea creatures
are about 2 billion years old. After all
the iron in the seas was used up to
form rock, oxygen released by these
organisms was added to the air.
C
Paleozoic Era
Crinoids are animals that flourished
during the Paleozoic Era. These
creatures lived anchored to the
ocean floor. There are some species
of crinoids that still exist today.
D
Mesozoic Era
Pterodactylus was a flying meateating reptile. It lived during the
Jurassic Period alongside dinosaurs.
The fossil record shows that these
animals went extinct at the end of the
Cretaceous Period.
The Geologic Time Scale
Paleogene Period
This fossil is of a horse-like mammal
from the Paleogene Period. During this
time, mammals diversified, leading
scientists to call this the “Age of
Mammals.” The first marine mammals
also appeared during this time.
E
Neogene Period
This skull is from one of the earliest
members of the genus Homo.
Modern humans, or Homo sapiens,
evolved about 200,000 years ago.
Divisions in Geologic Time
The geologic time scale is broken up
into the following divisions of time:
eons, eras, periods, and epochs.
Divisions in the geologic time scale are
not equal. This is because the divisions
are based on major events and
changes in Earth’s history, such as
extinctions.
Look at the clock-shaped diagram of
geologic time. If Earth’s history were
squeezed into 12 hours, Precambrian
time would take up most of that time.
Precambrian time began around the
time Earth formed and lasted for about
4 billion years. That is almost 90
percent of Earth’s 4.6-billion-year
history!
F
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Lab Summary page
Geologic Timeline Lab
Lab Summary
1. Using your lab, which has existed for a longer amount of geologic
time; Humans or Dinosaurs? Show evidence (math calculations) to
support your answer.
2. The geologic time line below represents the three most recent
geologic eras. The numbers represent events in Earth’s History.
Which number best represents when humans are inferred to have
first appeared on Earth?
_________
Lab Summary page
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Geologic Timeline Lab
Lab Summary
The Geologic History Clock
1. How many hours exist between the formation of Earth and the Origin of
life?
_____________
2. What percentage of time does this represent?
(# hours (above) ÷ 24 hours ) x 100
______________
3. How many minutes have humans been in existence?
______________
4. At what time were the oldest fossils?
_______________
5. Dinosaurs were in existence approximately how much time before
humans?
______________
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ESRT Geologic History of
New York State ………………………………
0
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Concept Review: Earth’s History
Multiple Choice Review
5. The geologic drill core below shows bedrock layers A,
*Use pages 26 and 27 to answer the questions below*
B, and C that have not been overturned. The geological
1. According to the Earth Science Reference Tables, which
ages of layers A and C are shown. What is the geologic
rock is most likely the oldest?
age of layer B?
(1) conglomerate containing the tusk of a mastodon
(2) sandstone containing fossils of flowering plants
(3) shale containing trilobite fossils
(4) siltstone containing dinosaur footprints
2. Which two forms of life existed together on the Earth
during the same time period? [Refer to the Earth Science
Reference Tables.]
(1) Condor and Bothriolepis
(2) Beluga Whale and Naples Tree
(3) Condor and Mastodont
(4) Coelophysis and Eurypterus
3. According to the Earth Science Reference Tables, which
event occurred at the time of the Alleghenian Orogeny?
(1) the development of birds and mammals
(2) the development of primitive aquatic plants
(3) the extinction of many kinds of dinosaurs
(4) the extinction of many kinds of land and marine animals
4. A geologist collected the fossils shown below from
locations in New York State.
(1) Ordovician (2) Permian (3) Devonian (4) Cambrian
6. According to the Earth Science Reference Tables, near
the end of which era did the dinosaurs become extinct?
(1) Cenozoic (2) Precambrian (3) Mesozoic (4) Paleozoic
7. For which segment of the Earth's geologic history are
fossils rarely found?
(1) Precambrian (2) Cenozoic (3) Paleozoic (4) Mesozoic
8. According to the Earth Science Reference Tables,
which geologic event occurred most recently in New
York State?
(1) The Taconic Mountains formed.
(2) The Palisades Sill intruded.
(3) A continental glacier covered most of the State.
(4) The entire State was uplifted from below sea level.
Which sequence correctly shows the fossils from oldest to
youngest?
9. According to the Earth Science Reference Tables,
which event was taking place during the Triassic Period?
(1) The Grenvillian Orogeny was raising the Adirondack
Mountains.
(2) The Palisades sill was intruding in the area of New
York State.
(3) The most recent continental glaciers were melting
over much of North America.
(4) Many kinds of marine animals, including trilobites,
were becoming extinct.
10. During which geologic time period did the earliest
reptiles and great coal-forming forests exist?
(1) Carboniferous
(2) Quaternary
(3) Devonian
(4) Cambrian
Geologic Time Review Worksheets
*USE PAGES 26 & 27 TO COMPLETE PAGES 29 & 30*
29
30
Geologic Time Review Worksheets
*USE PAGES 26 & 27 TO COMPLETE PAGES 29 & 30*
Lesson 2 Review: Self-Check
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Can You Explain It?
What evidence is used to construct this timeline of Earth’s History?
1.State your claim. Make sure your claim fully explains what evidence is used to
construct timelines of Earth’s history.
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
2. Summarize the evidence you have gathered to support your claim and explain your
reasoning.
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
32
Concept Review: Unit 4 Review
Multiple Choice Review
5. Index fossils have usually formed from organisms
1. The diagram below shows a cross-sectional view of part of
which had a
the Earth's crust. What does the unconformity (buried
erosional surface) at line XY represent?
(1) narrow geographic distribution and existed for a long
time
(2) wide geographic distribution and existed for a long
time
(3) wide geographic distribution and existed for only a
short time
(4) narrow geographic distribution and existed for only a
short time
(1) proof that no deposition occurred between the Cambrian
and Carboniferous periods
(2) overturning of the Cambrian and Carboniferous rock
layers
(3) a time gap in the rock record of the area
(4) an area of contact metamorphism
6. The fossil record indicates that most of the plants and
animals that lived on Earth in the past
(1) lived on land
(2) became index fossils
(3) have become extinct
(4) appeared during the Cambrian Period
2. According to the Earth Science Reference Tables, studies
of the rock record suggest that
(1) humans first appeared at the time of the intrusion of the
Palisades sill
(2) the period during which humans have existed is very brief
compared to geologic time
(3) evidence of the existence of humans is present over much
of the geologic past
(4) the earliest humans lived at the same time as the
dinosaurs
3. The diagram below represents a cross section of the
Earth's crust showing rock units and a fault. The rock layers
are not overturned. Which rock unit is the youngest?
(1) shale
(2) sandstone
(3) limestone
7. Some marine organisms swim or float in the ocean,
and others live on or in the sediment of the ocean floor.
A group of floating organisms called graptolites were
common in some ancient seas that covered New York
State and are found in some New York State bedrock.
State one reason why certain species of graptolites are
used as an index fossil.
______________________________________________
8. The diagram below represents the radioactive decay
of uranium-238 into stable lead Pb206. According to the
Earth Science Reference Tables, shaded areas on the
diagram represent the amount of
(4) basalt
4. Why are ancient volcanic ash deposits important to
geologists?
(1) They form resistant rock layers containing fossils.
(2) They are easily dated using carbon-14.
(3) They serve as good geological time makers.
(4) They indicate major areas where earthquakes occurred
(1) stable carbon-14 (C14)
(2) undecayed radioactive uranium-238 (U238)
(3) undecayed radioactive rubidium-87 (Rb87)
(4) stable lead-206 (Pb206)