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Geologic Time

What is Age?

• There are 2 kinds:

– Absolute Age – The number of years since the rock formed. (150 million years old, 10 thousand years old.)

– Relative Age – The age compared to the ages of other rocks. (older than this rock, younger than that rock.)

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Law of superposition

Which layer is oldest?

» Diagram this!

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Law of cross-cutting

Which layer is older 4 or 3?

» Diagram this!

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Law of Horizontality

Draw this!

A BREAK in the Earth’s crust.

A fault is always YOUNGER than the rock it cuts through.

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What is an Unconformity?

• The surface where new rock layers meet a much older rock surface beneath them.

• An unconformity shows where some rock layers have been lost because of erosion.

Unconformity

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Put in order!

Geologic time

Gigaannus:

Ga= Billion years

Billion years ago:

BYA

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Major divisions of geologic time

PrecambrianP

aleozoic

Mesozoic

Cenozoic

Early Earth History

Precambrian Longest time unit

Biological events Primordial puddle

Amino acids formed

Invertebrates developed

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Precambrian, contd…Geologic events

Very volcanic, many igneous rocks formed

Little is known about this era, because rocks were eroded, heated and pressurized, invertebrates are soft.

Paleozoic Era 544-286 MYA

Biological events

Mostly marine life forms:

Trilobites

Brachiopods and Crinoids still exist today

Fish

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Clicker• Divisions between ERAS in

geologic time is based on?

a)Mass extinctions

b)Ice ages

c)Exfoliation

d)Volcanic eruptions

TimerTimes up!

SMART Response QuestionTo set the properties right click and select

SMART Response Question Object->Properties...

Paleozoic, cont…

Appalachian Mountains started forming

First vertebrates

Plant life moved from ocean to land

Then animals moved to land.

Pangaea came together and major glaciers formed, caused mass extinctions of animals.

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Mesozoic Era 245-66.5 MYA

Divided into three periods:

Triassic

Jurassic

Cretaceous

Mesozoic, contd…

Triassic period Pangaea

separated

Climate dried out

Small dinosaurs appeared

First mammals

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Mesozoic, contd…

Jurassic

Reptiles dominated

Big dinosaurs!

Birds appeared

Mesozoic, cont’d

Pangaea breaks up (completely)

Volcanic activity

Dinosaurs become extinct

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Cenozoic, 66.4 MYA to present

Ice ages occurred

Himalayan mountains formed

Further evolution of plants and animals. Insects, small animals, Modern Humans appeared 200,000 years ago

Fossil

• Evidence such as the remains, imprints or traces of once living organisms preserved in rocks.

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Fossil types • Replacement fossil- form when bones, teeth or

shells are replaced by minerals dissolved in water.

• Carbonization fossil- forms when an animal is compressed, leaving behind a carbon film on the surrounding rock.

Fossil types Cast/Mold

• Cast- the part that is the shape of the original object.

• Mold- the cavity in the rock.

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Fossil types

• Original remains- insects can be completely preserved in crystallized tree sap (amber).

• Trace fossils- fossilized tracks and other evidence of animal activity.o Footprints

o Burrow holes

o Coprolites

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Michigan’s Geologic History

• Precambriano Metamorphic rock

o MI was tectonically active

o Copper and Iron

o Fossilized algae (stromatolites)

• Paleozoico MI was tropical

• Ocean (salt water)

• Coral => Petoskey stones

• MI basin bowl shaped

o Youngest rocks in the center older as you move away

Michigan’s Geologic History

• Mesozoico Jurassic rock the youngest what happened to the rest?

• Stolen!

• Unconformity

• What fossils would you not expect to find?

o Sorry no dinosaurs in your backyard

• Cenozoico Glaciers

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ABSOLUTE DATING

Absolute dating- Any method used to determine the age, in years, of a rock or other object. Radiometric Dating

Carbon dating

Uranium dating

Other methods dendrochronology

RADIOMETRIC DATING

Some isotopes of some elements break down (decay) into other elements over time. These are called radioactive isotopes.

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EXAMPLES OF RADIOACTIVE ISOTOPES

238Uranium decays to 206Lead

14Carbon decays to 16Nitrogen

Parent product daughter product

(Unstable) (stable)

RADIOMETRIC DATING

We know how long it takes uranium to decay to lead. This rate of decay is known as its half-life. This rate is quantifiable.

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HALF-LIFE

The half-life is the time it takes for half of the atoms of the parent product to decay to the daughter product.

14C = 5,730 years

238U = 4.5 billion years

40K = 1.248 billion years

C-14 C-14 N-161 half life

It would take 5,730 years for half of the 14C atoms in an object to decay to 16Nitrogen