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Lecture 25

EPS 7 Lecture Notes - Lecture 25: Greenhouse Gas, Megafauna, Runaway Greenhouse Effect

Earth And Planetary Science
Course Code
David Romps

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Lecture 24 10/23/17
Paleoclimate: the past as guide to the future
Midterm: radio transfer to scary feedback
Ice house (snowball earth)
Hot house (runaway greenhouse)
a) Snowball earth is where the oceans are entirely frozen, all the way down to the
b) An icehouse climate is one in which there are ice sheets at the poles
c) A hot house climate is one in which there are no glaciers, not even at the poles
d) Runaway greenhouse is where the total feedback becomes positive, causing the
oceans to boil
(earth has not explored this climate state, but our neighbor has)
Mercury Venus earth mars Jupiter Saturn Uranus Neptune
1) Same size as earth
2) Had oceans of water
3) Was a candidate for life
4) Now a runaway greenhouse climate
- Venus has a runaway greenhouse climate
- Venus started out like earth, with an ocean suitable for life
- The positive water vapor feedback became so big, that the total feedback parameter
was positive
- With a positive feedback, Venus got hotter and hotter
- The oceans boiled and the water vapor escaped to space
- Today, its atmosphere is almost entirely CO2
Mercury (closer to the sun) 440K
Venus (farer from the sun but hotter) 737K
Video- death of an apple on Venus
All of Earth history
a) Precambrian
1) 4.5 Gya Earth formed
2) 2.5 Gya Great oxygeneation event (snowball earth)
3) 0.5 Gya Multicellular life begins
- What triggered these snowball earth events?
For the first one, it was albedo effect
Somehow gets cold enough that the positive ice-albedo feedback takes over
b) Phanerozoic Eon
1) Paleozoic 542 Mya: age of weird critters (oceans full of weird creatures)
--------- 251 Mya: Great dying: cause unknown---------
2) Mesozoic Age of dinosaurs
--------- 65 Mya: Asteroid kills dinosaurs------------
3) Cenozoic Age of mammals
One dinosaur survives: the one that looks like bird, reptiles, and mammals
In the Mesozoic, the reptiles were big and the mammals were small
The dinosaurs snacked on the mammals, far less often the other way around
- What happened to these North American mega fauna?
Mega fauna means large animals
The Native Americans ate them
- Why is the Cenozoic the age of mammals?
- Why are mammals the Cenozoic mega fauna?
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