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

Dinosaurs

Age of the Fishes

Soft-Bodied Animals

Bacteria Stromatolites

No 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 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 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 age, again?

Deeper Rocks Are Warmer! Deeper Rocks Are Warmer!

1859- Lord Kelvin Believed Earth was originally molten, & still losing heat Aged Earth at million years in age

Early Radiometric Dating Will you be my 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 forests Age of fishes! First amphibians & forests Bacteria and algae Humans/Mammals Warm, sea level rise, dinosaurs die out at end Many new organisms, early dinosaurs, ammonites Hot and dry, Mass Extinctions! First fish and land plants Inverterbrates and early verterbrates (jawless fish) widespread seas, earliest fossils (trilobites) Dino’s died, mammals diversified, flowering plants diversified