Ice Ages

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The Carbonate-Silicate Cycle

Mountain-building favors cooling

Uplift exposes rocks to weathering

Calcium silicates (plagioclase, amphiboles, pyroxenes) are chemically weathered

Calcium is carried to the sea where organisms bind it into carbonate minerals

Creation of carbonates removes carbon dioxide from the atmosphere

Weathering of carbonates returns carbon dioxide to the atmosphere

Slide 13

The Carbonate-Silicate Cycle

Plate tectonics carries some carbonates into the earth

Heat liberates carbon dioxide

Carbon dioxide returns to the atmosphere

The cycle does not require life but does require liquid water.

Slide 14

The Snowball Earth

Between 900 and 600 m.y. ago, Earth froze completely (or almost) about four times

Global freezing alternated with extremely rapid sea-level rise and global warming

Evidence:

Glacial deposits on all continents, even at low latitudes

Glacial deposits immediately succeeded by thick deposits of carbonate rocks

Slide 15

The Snowball Earth

Possible reasons:

Fainter early sun

Biological changes

Global ice cover

Weathering and erosion shut down

Volcanoes continue to erupt CO2

At 10% CO2, abrupt warming begins

Go from –50 C to +50 C in 10,000 years?

Implications for life?

Slide 16

What Causes Ice Ages?

Within Earth (Endogenic)

Carbonate-Silicate Cycle

Volcanic Eruptions - Sudden output of CO2 (warming) or particulates (cooling)

Mountain Building - Changes in atmospheric circulation

Continent-Ocean configuration

Outside Earth (Exogenic)

Changes in Sun (faint early sun)

Variations in Earth Orbit (Milankovitch Cycles)

Don't Really Know

Slide 17

Are We Headed For Another Ice Age?

Heating & Cooling in Historic Times

Smoke, Haze, CO2 May Alter Climate

Don't Really Know

Global warming due to fossil fuels may be catastrophic in many ways, but will probably not much affect these longer-term cycles. We will have run out of fossil fuels long before the duration of a typical interglacial.