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Hoffman's Pan-glacial state - Coggle Diagram
Hoffman's Pan-glacial state
3 distinct climate types (on earth)
non-glacial
no continental ice sheets
glacial-interglacial
High latitude ice sheets
Pan-glacial
Ice sheets at all latitudes ("pan" = all)
Development of the model
1926
it was thought that the Earth only went through non-glacial and glacial-interglacial states
Proterozoic eon: glacial sheets forming on ALL continents (panglacial)
with a mere 1.5-2.0% drop in solar radiations, surface temps fall drastically
the sun's luminosity was 25-30% lower back in the day (early solar system)
1980s
Negative feedback cycle of Carbon prevents snowball earth from being permanent
"white earth" disaster is self-reversing
Snowball earth hypothesis formulated
1960s
Ice sheets found to have existed on mountainless marine carbonate platforms
these are warmer areas of the surface ocean
if they exist here^, they MUST have existed in colder (higher) latitudes
Credence to the snowball earth model/panglacial earth
Conclusions
There is consensus on a panglacial earth
However, scientists are split between:
Snowball model
Slushball model
How does a global ice shelf work?
Ice sheet thickness is governed by:
geothermal heat from bottom of the ocean
surface air temperature
sublimation/melting @ low latitudes
freezing/condensation @ middle to high latitudes
Ice sheet is composed of:
Meteoric ice: Compressed snow. This ice, owing to the trapped air bubbles, has a higher albedo
Marine ice: Frozen sea water.
Machinations:
equatorial ice sheets are thinner if marine ice is exposed (due to sublimation). Lower albedo = more heat absorbed = thinner ice
equatorial ice sheets are thicker if meteoric ice covers
Evidence(s) for panglacial earth
Banded Iron-Manganese formations (BIFs)
sedimentary deposits due to anoxic waters of the neoproterozoic period
Cap carbonates
fallout of the panglacial period: mass melting, high surface temps = heightened ocean alkalinity = formation of carbonates
glacioeustatic consequences
Biosphere response
Large amounts of environmental stress lead to Cambrian
EXPLOSION