Deep Time:An Introduction to Geologic Time

•How far back into your family history can you remember?

•Maybe 100 years?

My Grandfather

In the grand

scheme of our

planet, 100 years

is the blink of an

eye

Let’s travel back...

Human Civilizations

Human Civilizations

DinosaursDinosaurs

Age of the Fishes

Soft-Bodied Animals

Soft-Bodied Animals

BacteriaStromatolites

No Life At AllNo Life At All

(Image: Mars)

...Still not even half way back through deep time...

Age of the Earth?•As

science has developed, so has our knowledge about the age of the Earth

Do You Recall Its Age?

The age of the Earth has been increasing with every

new discovery!

Historic Estimations

Originally:

Historic Estimations•Written history

•Ocean Salt

•Thickness of Sedimentary Layers

•Temperature

•Early 1900’s Radiometric Dating

Biblical & Other Calculations

•Archbishop James Ussher

•1640- First known scientific study of the age of the Earth

•Used Hebrew chronology (Begat theory)

•Aged Earth to 4004 BC

Biblical & Other Calculations•Christian estimates at

the time:

•Earth’s age= 6,000 years

•SIMILAR

Can We Be More Precise, Please?•Theologians were not

satisfied

•Further interpreted the actual “Birth of the Earth” to be:

•October 23, 4004 BC...

•...at 9 o’clock a.m.

Other Religions•Some

religions have a cyclic belief, that the Earth has no beginning and will have no end

Ocean Salt Estimations

•Suggested age of the Earth could be calculated by measuring the amount of salt in the ocean

•Assumptions:

•Oceans began as Fresh Water

•Oceans got salty from runoff from the continents

•Idea: Measure amount of salt in the ocean, then measure it again 10 years later

1715- English Astronomer Edmund

Halley

1899- John Jolly

•Actually uses an idea similar to Halley’s, but with some adjustments

•Calculation:

•Age of the Earth= 90 million years old

Issues with the “Ocean Salt” Idea•Despite oceans initially being

fresh water, their salinity is relatively constant

•Ocean salinity is in equilibrium with the salt in the rocks of the lithosphere

Thickness of the Sedimentary

Layers

•Estimating age of the Earth by measuring the total thickness of rock layers

•Assumption: each rock type has an average rate of deposition

Results

•Didn’t work. Why?

Estimations Using

Heat Loss

What’s my What’s my age, again?age, again?

Deeper RocksAre

Warmer!

Deeper RocksAre

Warmer!

1859- Lord Kelvin•Believed

Earth was originally molten, & still losing heat

•Aged Earth at 20-100 million years in age

Early Radiometric

DatingWill you Will you be my be my

valentine?valentine?

Will you Will you be my be my

valentine?valentine?

Radioactive Decay of Elements•Henry Becquerel

•French physicist, 1896

•Uranium emits “mysterious rays”- can expose photographic paper even in the dark

Radioactive Decay of Elements

•Madame Marie Currie

•Expanded on this knowledge for her doctorate

•Named this phenomenon “radioactivity”

STOP

•What do we already know about radioactivity, radioactive decay, & radiometric dating?

•If time- fill in details on time scale

Large reptiles & dinosaurs dominate land and sea, ammonites, first birds

(archaeopteryx)Seed bearing plants, coral reefs, coal forming

forestsAge of fishes! First amphibians & forests

Bacteria and algae

Humans/Mammals

Warm, sea level rise, dinosaurs die out at end

Many new organisms, early dinosaurs, ammonitesHot and dry, Mass Extinctions!

First fish and land plantsInverterbrates and early verterbrates

(jawless fish)widespread seas,

earliest fossils (trilobites)

Dino’s died, mammals diversified, flowering

plants diversified