deep time: an introduction to geologic time. how far back into your family history can you remember?...
Post on 21-Dec-2015
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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