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Snowball Earth - PowerPoint PPT Presentation


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Snowball Earth . History of Glaciation. Main Periods of Glaciation. Huronian glaciations 2.5-2.2 billion years ago Late Proterozoic glaciations 900-545 million years ago Late Ordivician glaciations 446-440 million years ago Permo-carboniferous glaciations 310-270 million years ago

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slide1

Snowball Earth

History of Glaciation

main periods of glaciation
Main Periods of Glaciation

Huronian glaciations

2.5-2.2 billion years ago

Late Proterozoic glaciations

900-545 million years ago

Late Ordivician glaciations

446-440 million years ago

Permo-carboniferous glaciations

310-270 million years ago

Pleistocene glaciations

1.8 million – 10,000 years ago

huronian glaciations
Huronian Glaciations

How do we get glaciers in a methane-rich atmosphere?

- rise of O2 atmosphere 2.3 bya

- elimination of methane in atmosphere

- decreased greeenhouse gases

- Earth enters deep-freeze

Evidence?

huronian glaciations evidence
Huronian Glaciations: Evidence

Kump, Kasting, and Crane (2004)

snowball earth late proterozoic glaciation
Snowball EarthLate Proterozoic Glaciation

Glaciation on 6 of 7 continents

- Antarctica: maybe was glaciated but too much

ice today to tell

Evidence: tillites, glacial striations, dropstones

Continental reconstructions show land was centered

around equator

slide7

Carbonate cap above glacial dropstones in Namibia

http://www-eps.harvard.edu/people/faculty/hoffman/snowball_paper.html

how did earth cool
How did Earth Cool?

Less solar luminosity – about 6% less than today

Removal of CO2 from atmosphere

continents at equator – silicate weathering even

as Earth cools

slide10

http://www-eps.harvard.edu/people/faculty/hoffman/snowball_paper.htmlhttp://www-eps.harvard.edu/people/faculty/hoffman/snowball_paper.html

how did earth cool11
How did Earth Cool?

Polar ice sheets form at poles and grow

increased albedo

decreased surface temperatures

slide12

http://www-eps.harvard.edu/people/faculty/hoffman/snowball_paper.htmlhttp://www-eps.harvard.edu/people/faculty/hoffman/snowball_paper.html

how did earth warm
How did Earth warm?

Earth completely frozen

Silicate weathering ceases

CO2 outgassing continues

Ice starts melting

decreased albedo

increased suface temperatures

times temps and rates
Times, temps, and rates

Glaciers freezing from 30 degrees to equator

- decades

Surface temperature = -40 or -50 degrees C

CO2 buildup during Snowball Earth

- 10 million years

Entire disappearance of glaciers after CO2 buildup

- thousands of years

CO2 rich atmosphere, low albedo

- surface temperature = 50 or 60 degrees C

Silicate weathering increases, climate system restored