Geologic History

Geologic History

Topic: Geologic Time

Objectives: Day 1 of 3

• I will know the major geologic events that have transformed our earth

• I will know the geologic time scale and it’s major divisions

Quickwrite:

In 2-3 sentences answer one of the questions below:

• What do you think a mass extinction is???• If you know what a mass extinction is, what

do you think causes them????• Considering the age of the earth 4.6 BYO,

When do you think life first appeared??

• The geological time scale is the geologic history of the planet from formation to the present.

• It is starts with large divisions of time called eons and is subdivided into successively smaller units such ass eras and period

• The geologic time scale is based on dominant lifeforms, and mass extinction events

Geologic Time Scale

Geologic Time ScaleSome of the major time

eras include the:

• Precambrian Oceans and atmosphere form

• Paleozoic Invertebrates, plants and fish are the

dominant forms of life

• Mesozoic Reptiles are the dominant forms of life

• Cenozoic Mammals are the dominant forms of life

What is the Geologic Time Scale?

• Time scale from the beginning of earth to present

• It is broken into time divisions such as Eras, & Periods that are based on the ____record, dominant life forms, and mass ____events

Answer BankExtinction

90%MeteoritesExplosion

FossilOxygenHumans

Photosynthesis

It was a harsh environment.Meteorites bombarded our earth

And volcanoes spewed out gases

Our oceans slowly formed over millions of yearsAs volcanoes released steam

One of these gases was steam or (H2O)

4.6 billion years agoEarth Forms

CO2N2CO2CO2H2OH2OH2O

This was what our planet was like for 4 billion years--90% of earth’s History

Scientists call this period the Precambrian

Precambrian

During the Precambrian, our oceans and atmosphere formed

along with other important events

Steam cooled and condensed into clouds,These clouds Released precipitation (rain) for

millions of years, eventually forming our oceans

Welcome to Earth 4.6 Billion Years ago

4.6 billion years agoEarth Forms

CO2CO2CO2

Precambrian

Another gas given off by volcanoes is Carbon Dioxide (CO2)

These microscopic phytoplanktonabsorbed CO2 from volcanoes and through

Photosynthesis released Oxygen (O2) into our atmosphere

Another important event during the Precambrian was the appearance

of the first single celled forms of life

These phytoplankton were very important Because they helped create an oxygen

rich atmosphere for life to thrive in

About 2 billion years ago, primitive microscopic single celled forms of life called

Phytoplankton began to fill the oceans

Remember the recipefor Photosynthesis is:

CO2 + H2O O2 + C6H12O6

O2O2O2

As Oxygen fill our atmosphere, Our skies eventually became Blue

How did our atmosphere become rich in oxygen?

• Primitive phytoplankton and algae bacteria called stromatolites released oxygen into our atmosphere through

_____ about 2 bya

Answer BankExtinction

90%MeteoritesExplosion

FossilOxygenHumans

Photosynthesis

PrecambrianPrecambrian

3.8 bya- first oceans form

2 bya- oxygen rich atmopshere forms

3.5 bya- 1st single celled forms of life

Major Geologic Events of the Precambrian Era

1.1bya-1st continentRhodinia forms

1.3 bya- first multi celled forms of life

4.5 bya- Moon forms

What are major geologic events of the Precambrian Era?

• 3.8 bya- oceans form

• 3.5 bya- 1st single celled forms of life

• 2 bya- ____ rich atmosphere forms

• 1.3 bya- 1st multi celled forms of life

• 1.1bya-1st continent Rhodinia forms

Answer BankExtinction

90%MeteoritesExplosion

FossilOxygenHumans

Photosynthesis

Some of these animals included trilobites,ammonites (squid like creatures with shells)

Paleozoic EraThe Paleozoic Era witnessed an explosion of life

Very shallow seas covered most of the earth

PrecambrianPrecambrianPaleozoic

Paleozoic

Through out these shallow seas lived some of the first complex forms of life Including: invertebrates (shell fish), fish and plants

PrecambrianPrecambrian

Major Geologic Events of the Paleozoic Era

Paleozoic

Paleozoic

PrecambrianPrecambrian

Paleozoic

Paleozoic

570 mya- Explosion of life

536 mya- 1st fish & invertebrates appear

513 mya- First land plants appear

322 mya- First reptiles appear

245 mya- Mass Extinction 90% of all life

Major Geologic Events of the Paleozoic Era

What are major geologic events of the Paleozoic Era?

• 570 mya- _____ of life• 536 mya- 1st fish & invertebrates

513 mya- 1st land plants • 322 mya- 1st reptiles appear• 245 mya- Mass Extinction ___%

of all life

Answer BankExtinction

90MeteoritesExplosion

FossilOxygenHumans

Photosynthesis

Mesozoic EraThe Mesozoic Era was the age of reptiles & witnessed the evolution of the largest animals to have ever walked the earth PrecambrianPrecambrian

Paleozoic

PaleozoicM

esozo

ic

Meso

zoic

The dinosaurs would eventually go extinct and give rise to modern day birds

However, as we all know, these dinosaurs died Out and left a world for other animals to inherit

Dinosaur Demise

• There is mounting evidence that a large meteorite impact slammed into earth 65 mya ending the Cenozoic era

• This impact would have caused widespread devastation and fires

Dinosaur Demise

• Ash and smoke from fires could have blocked out enough sunlight changing the global climate; decimating and wiping out the cold blood reptiles

PrecambrianPrecambrian

Major Geologic Events of the Mesozoic Era

Paleozoic

PaleozoicM

esozo

ic

Meso

zoic

PrecambrianPrecambrian

Paleozoic

PaleozoicM

esozo

ic

Meso

zoic 200 mya- First Mammals appear

180 mya- Pangea breaks up

160 mya- First Birds appear

65 mya- Mass extinction 60% of all life perishes

200 mya- First Mammals appear 200 mya- First Mammals appear

Major Geologic Events of the Mesozoic Era

What are major geologic events of the Mesozoic Era?

• Reptiles dominate• 200 mya- 1st small Mammals appear• 180 mya- Pangea breaks up• 160 mya- 1st Birds• 65 mya- Mass extinction 60% of all life

perishes including dinosaurs due to large ______collision

Answer BankExtinction

90%MeteoritesExplosion

FossilOxygenHumans

Photosynthesis

Cenozoic EraWith Dinosaurs gone, Mammals would inherit

the earth and dominate the landLarge mammals thrive such as

Horses, Mammoths, and Primates

Mankind would evolve and inhabit the earth expanding it’s population

Many Ice Ages came in went causing the extinction of many large mammals

PrecambrianPrecambrian

Paleozoic

PaleozoicM

esozo

ic

Meso

zoic

Cen

ozo

icC

eno

zoic

PrecambrianPrecambrian

Paleozoic

PaleozoicM

esozo

ic

Meso

zoic

Cen

ozo

icC

eno

zoic

Major Geologic Events of the Cenozoic Era

Major Geologic Events of the Cenozoic Era

PrecambrianPrecambrian

Paleozoic

PaleozoicM

esozo

ic

Meso

zoic

Cen

ozo

icC

eno

zoic

45 mya- One of the largest Ice ages occur

7 mya- First Human Ancestors appear

300,000 ya- Modern humans appear

What are major geologic events of the Cenozoic Era?

• Mammals dominate

• 45 mya- Major ice age event

• 7 mya- 1st Human ancestors appear

• 300,000ya- 1st modern ____• Present- your writing this down!!!!! (do not

write )

Answer BankExtinction

90%MeteoritesExplosion

FossilOxygenHumans

Photosynthesis

Summarize:

List the events in order: Oldest to youngest

• Mammals dominate the earth• Mass extinction 90% of all life wiped out• Reptiles dominate the earth• Explosion of life• Phytoplankton create oxygen rich atmosphere• Mass extinction 65% of all life wiped out including

dinosaurs

Topic: Relative Dating

Objectives: Day 2 of 3

• To learn how scientists use relative dating techniques to put geologic events in order

• To learn how to apply the laws of geology (the law horizontality, law of superposition, law of cross-cutting relationships) to relative dating

Quickwrite:

In 2-3 sentences answer one of the questions below:

• How do you think scientists know which fossils are older and which fossils are younger?

• Imagine you have a full trash can, where would you find the old trash??? Where would you find the new trash???

Relative Dating• In our last notes, we learned

the history of the earth, when reptiles first appeared, when dinosaurs went extinct, when mammals dominated earth

• So how do we know the order of all these events?

• One way scientist’s have figured out Earth’s History is by Relative Dating

Relative Dating• Relative Dating is the concept of dating rocks

by putting geologic events in order• It does not give an exact age of rocks

3.

2.

1. 4. Magma Intrusion

8.

7.

5. Fault cuts through

What is Relative Dating?• The concept of dating rocks by putting

geologic events in_______

3.

2.

1. 4. Magma Intrusion

8.

7.

5. Fault cuts through

Answer BankYounger

gapTop after

BottomOrder

flat

Law of Superposition

3.

2.

1.

• In layers of deposited sedimentary rock, the oldest rock layers are at the bottom and the rock layers become younger toward the top

• Therefore, older fossils would be ath the bottom and younger fossils would be closer to the top

Law of Superposition• Principle of Superposition: States that the

oldest rock layers are at the bottom and the rock layers become younger toward the top

The Law of Superposition: Old rocks formed on the bottom and young rocks are at the top

Young rocks

are at the top

Old rocks are

at the bottom

What is the Law of Superposition?

3.

2.

1.

• In layers of deposited sedimentary rock, the oldest rock layers are at the ____ and the rock layers become younger toward the ____

Answer

BankYounger

gapTop after

BottomOrder

flat

Law of Horizontality

Law of Horiz

ontality:

Rocks f

all into

place fo

rming fla

t,

horizontal la

yers

Law of Horizontality Sediments are originally deposited in flat horizontal layers. If

the rocks are folded or are laying at a steep angle, they must have been disturbed or tilted after they were originally

deposited.

3.

2.

1.

3.

2.

1.

What is the Law of Horizontality?

Sediments are originally deposited in ____ horizontal layers. If the rocks are folded or at an angle, they must have been

disturbed _____they were originally deposited.

3.

2.

1.

3.

2.

1.

Answer Bank

YoungergapTop after

BottomOrder

flat

Unconformities• Think of layers of rock as pages of a history

book • If we remove pages, the book is incomplete• An unconformity is when layers of rock are

missing

3.

2.

1. 1.

3.

Unconformities:Here’s how it works!!!!

3.

2.

1.

5.

4.3. Unconformity(weathering and erosion

create a gap in geologic time)

Unconformities• An unconformity is a gap in rock layers due to

erosion and weathering or a break in the depositing of sediments (missing rock layers)

3.

2.

1. 1.

3.

What is an Unconformity?• An unconformity is a ____ in rock

layers due to erosion and weathering or a break in the depositing of sediments (missing rock layers)

3.

2.

1. 1.

3.

Answer BankYounger

gapTop after

BottomOrder

flat

3.

2.

1. 4. Magma Intrusion

5. Fault cuts through

Law of Cross Cutting Relationships

• The law of cross cutting relationships states that a fault line or an igneous intrusion must be younger than the rock it cuts across.

3.

2.

1. 4. Magma Intrusion

5. Fault cuts through

What is the Law of Cross Cutting Relationships?

• A fault line or an igneous intrusion must be _____ than the rock it cuts across.

Answer BankYounger

gapTop after

BottomOrder

flat

Practice:Start with the oldest rock and work your way to the youngest

C

B

A D Magma Intrusion

H

G

E Fault cuts through

Young1.2.3.4.5.6.7.8.Old

F

A

B

C

D

EF

GH

C

B

A D Magma Intrusion

H

G

E Fault cuts through

F

Practice:Start with the oldest rock and work your way to the youngest

C

B

A D Magma Intrusion

H

G

E Fault cuts through

Young1.2.3.4.5.6.7.8.9.Old

F

A

B

C

D

EF

GH

C

B

A D

H

G

E

FKK

K

Summary:• The law of ______ states that

Sediments are deposited in flat horizontal layers

• When rock layers are missing in the geologic record we call it an _______

• The law of ____ ____ relationships states that A fault line or an igneous intrusion must be younger than the rock it cuts across.

Answer Bank

unconformityhorizontality

Cross-cuttingsuperposition

Topic: Absolute Dating

Objectives: Day 3 of 3

• I will know how scientists use absolute dating to determine the exact age of rocks

• I will know the concept of half life and radioactive decay

Quickwrite:

In 2-3 sentences answer one of the questions below:

• If you shook up 100 pennies in a box, how many do you think would be heads???? How many do you think would be tails????

• Let’s say you have 100 dollars and you can only spend half of it every day. How much money would you have after 2 days????

Absolute Dating• How do we know the earth is

4.6 billion years old?• How do we know when

dinosaurs went extinct?• We can answer those questions

by using Absolute Dating• Absolute Dating is a method

used by geologists to determine the exact age of a rock or fossil

• By analyzing the properties of atoms in rocks and fossils we can get a really accurate date for when the rock or fossil formed

What is Absolute Dating?

• Absolute Dating is a method used by geologists to determine the exact _____ of a rock or fossil

• Different from relative dating because it gives an exact age

Answer Bank

ElementAge

determinedecay

Radioactive Decay• Radioactive Decay: The decay of one

element into another element, • An example would be when Uranium

becomes Lead• Uranium is the parent material and lead is the

what we call the daughter materialUranium Lead

Uranium Atom

Parent Material (unstable) Daughter Material (stable)

Lead Atom

What is Radioactive Decay?• The decay of one element into

another _____

• Ex. Uranium, the unstable parent material decays into the stable daughter product Lead

Answer Bank

ElementAge

determinedecay

Uranium Lead

Uranium Atom

Parent Material (unstable) Daughter Material (stable)

Lead Atom

• Half life is the time it takes for half of the of the parent material to decay

• For example, suppose I have a rock sample that has 100 atoms of Uranium in it

• The Half-Life of Uranium is 4.5 billion years

• So after 4.5 billion years (1 half life) half of the Uranium will have decayed into Lead

• So after 1 half life, you are left with 50% Uranium and 50% Lead

Half-Life

1 half life = 4.5 by

= Uranium

= Lead

50 atoms of Uranium

50 atoms 50 atoms of Leadof Lead

• How much Lead and Uranium is left after another 4.5 billion years (2 half lives) ?????

• Lets find out!!!!!• The Half-Life of Uranium is

4.5 billion years• So after another 4.5 billion

years (2 half lives) half of the Uranium will have decayed into Lead

• So after 2 half lives, you are left with 25% Uranium and 75% Lead

Half-Life

= Uranium

= Lead

second half life = 4.5 by

25% Uranium

75% Lead

• How much Lead and Uranium is left after another 4.5 billion years (3 half lives) ?????

• Lets find out!!!!!• So after another 4.5

billion years (3 half lives) half of the Uranium will decay into Lead

• So after 3 half lives, you are left with 12.5% Uranium and 87.5% Lead

Half-Life

= Uranium

= Lead

1st Half Life = 4.5 by

12.5% Uranium

87.5% Lead87.5% Lead

2nd Half Life = 4.5 by

3rd Half Life = 4.5 by

What is Half life?• Half life is the

time it takes for half of the of the parent material to _____

• Ex. Uranium has a half life of 4.5 billion years

Answer Bank

ElementAge

determinedecay

1 half life = 4.5 by

50 atoms of Uranium

50 atoms 50 atoms of Leadof Lead

Who thinks they understand half-life?

1) What is the half life of uranium-238?

2) According to this diagram, how much uranium remains after 4.5 Billion years? Lead?

3) After 9 billion years, how much uranium is left? Lead?

= parent material

= daughter material

½ life = 50,000 yrs

50,000 yrs

100% Parent Material

50,000 yrs

50% Daughter Material50% Parent Material

75% Daughter Material25% Parent Material

87.5% Daughter Material12.5% Parent Material

Number of Half Lives

Am

ount

of

Par

ent

Mat

eria

l

75

100

50

2550,000 yrs 50,000 yrs 50,000 yrs

1 2 3 4 50

Old vs. Young Rock• We use Uranium half life to measure the age

of the earth, which is very old• But, how would we measure something that is

younger, like tree rings or artifacts from an ancient land?

• Because Carbon-14 ( a radioactive form of carbon) has a half-life of 5,730 years, we can use it to date rocks that are much younger (unlike uranium, which has a half-life of 4.5 billion years)

• After 5,730 years Carbon-14 will decay into stable Nitrogen

Radiometric Dating• To a geologist who studies rocks

in order figure out earth’s history, these radioactive elements that decay are like a clock ticking away, keeping track of time since that’s passed since earth formed

• Radiometric dating has allowed us to figure out Earth’s history in chronological sequence

• Radiometric Dating: A dating method that uses the rate of decay of radioactive atoms in rocks by the amount of parent and daughter product to determine the absolute age of a rock

What is Radiometric Dating?

• Dating method that uses the rate of decay of radioactive atoms in rocks by the amount of parent and daughter product to _____ the absolute age of a rock

Answer Bank

ElementAge

determinedecay

Summarize:• Read the following scenario to complete the

answer below: A piece of coal (made of carbon) from a cave man’s fire is found to have about 50% Carbon-14 and 50% Nitrogen. The half life of Carbon-14 is 5730 years.

1. Carbon-14 is the _____ material and Nitrogen is the _____material

2. ______ is the half life of Carbon-143. The caveman’s coal and fire is ______years

old4. Scientist’s use _____dating to determine the

absolute ____of rocks and fossils

Answer BankParentage

DaughterRadiometric

5,730

100%Carbon-14

5,730years50%

Carbon-1450%

Nitrogen