Geologic Time

Geologic time

Gigaannus: Ga= Billion years

Billion years ago: BYA

Major divisions of geologic time

Precambrian

Paleozoic

Mesozoic

Cenozoic

Early Earth History

Precambrian Longest time unit

Biological events Primordial puddle Amino acids

formed Invertebrates

developed

Precambrian, contd…Geologic eventsVery 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 eventsMostly marine life forms:

Trilobites Brachiopods and

Crinoids still exist today

Fish

ClickerClicker• Divisions between ERAS in

geologic time is based on?

a)Mass extinctionsb)Ice agesc)Exfoliation d)Volcanic eruptions

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A96%

D4%

SMART Response Quiz Results (Correct answer:A)

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.

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

Mesozoic, contd…

Jurassic Reptiles

dominated Big dinosaurs! Birds appeared

Mesozoic, cont’d

Pangaea breaks up (completely)

Volcanic activity

Dinosaurs become extinct

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 Fossil • Evidence such as the remains, imprints or traces

of once living organisms preserved in rocks.

ClickerClickerWhen watching an old movie of Stone Age people battling dinosaurs, you should know the story in the movie is fiction because

A. stone age people were intelligent enough to avoid dinosaurs.

B. stone age people and dinosaurs were not in competition for the same food.

C. stone age people and dinosaurs lived at the same time, but in different environments.

D. stone age people and dinosaurs did not exist at the same time.

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Fossil types 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 Fossil types Cast/Mold•Cast- the part that is the shape of the original object.

•Mold- the cavity in the rock.

Fossil types 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 Footprintso Burrow holeso Coprolites

Michigan’s Geologic Michigan’s Geologic HistoryHistory

• Precambriano Metamorphic rocko 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 Michigan’s Geologic HistoryHistory

• 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

ClickerClicker

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A92%

B4%

C4%

SMART Response Quiz Results (Correct answer:A)

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.

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.

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