Ice Ages

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Slide 1

Ice Ages

Pleistocene 3 M.y.

Permian 250-220 M.y.

Ordovician 450 M.y.

Precambrian

900-650 M.y. (Snowball Earth)

2300 M.y.

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Slide 3

The Last 800,000 years

Slide 4

Beginning of the Ice Ages

Slide 5

Milankovich Cycles

Cool Summers More Important Than Cold Winters

Tilt of Axis

Shape of Orbit

Precession

Can’t be the whole story-have operated throughout earth history

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Axis Tilt

Small Axis Tilt: Mild winters but cool summers. Favors Ice Age

Large Axis Tilt: Cold winters but hot summers. Favors Interglacial

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Axis Tilt and the Incredible Shrinking Tropics

Earth’s Axis Tilt is Shrinking

24.2 degrees 9,500 years ago

23.4 degrees now

22.6 degrees 10,200 years from now

Tropics are shrinking

14.7 m/year = 4 cm/day = 1.7 mm/hour

Temperate zones gain 1550 sq km/year

1080 at the expense of tropics

470 at the expense of Arctic and Antarctic

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Precession: 26,000 year cycle

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Shape of Orbit + Precession

Summer at Perihelion (Eccentric Orbit)

Cold winters but hot summers. Favors Interglacial

Summer at Aphelion (Eccentric Orbit)

Near-circular Orbit

Mild winters but cool summers. Favors Ice Age

Slide 10

The Greenhouse Effect

Without a natural Greenhouse Effect, earth would be frozen

90% due to Water Vapor

Other contributors: carbon dioxide, methane, nitrous oxides

“A little Greenhouse Effect is a good thing”

Carl Sagan

Problem: we are accelerating it with unknown final consequences

Slide 11

The Carbonate-Silicate Cycle

Earth has almost as much carbon dioxide as Venus

Volcanoes add carbon dioxide to the atmosphere

Carbon dioxide is removed from the air to make carbonate rocks

“Icehouse” and “Greenhouse” episodes

Slide 12