Snowball Earth

1
Snowball Earth
History of Glaciation
2
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
3
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?
4
Huronian Glaciations Evidence
Kump, Kasting, and Crane (2004)
5
Huronian Glaciations Recovery
CO2 outgassing
6
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
7
Carbonate cap above glacial dropstones in Namibia
http//www-eps.harvard.edu/people/faculty/hoffman/
snowball_paper.html
8

• Bagganjarga tillite and striated bedrock in Norway

9
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
10
http//www-eps.harvard.edu/people/faculty/hoffman/
snowball_paper.html
11
How did Earth Cool?
Polar ice sheets form at poles and
grow increased albedo decreased surface
temperatures
12
http//www-eps.harvard.edu/people/faculty/hoffman/
snowball_paper.html
13
How did Earth warm?
Earth completely frozen Silicate weathering
ceases CO2 outgassing continues Ice starts
melting decreased albedo increased suface
temperatures
14
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