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Initial Paradoxes (W/O the model)
Occurence of glacial debris in the tropics near sea level (I)
Unusual deposits of Iron rich rock (II)
Formation of carbonates just after glacial recession (III)
Carbon isotopes in rocks showed a decrease in biological productivity (IV)
Snowball Earth Stages
Stage 1
Increased rainfall = less atmospheric CO2
^Leads to falling temperatures
^Ice accumulation @ the poles = higher planetary albedo
^Feedback loop leading to more ice formation = unstoppable cooling!
Intombs the planet in ice! (Lissandra)
Stage 2
Average planetary temp: -50 degrees Celsius
Oceans are frozen up to 1km deep
Most organisms die: extremophiles @ volcanic springs survive
Cold dry air = no rainfall
^Volcanic CO2 remains in the atmosphere
^ Causes the planet to warm slowly = ice thaws slowly
Stage 3
Increased CO2 concentrations (x1000) after 10million years of Volcanic activity
^pushes equatorial temps to melting pt.
Land glaciers grow (due to more moist air)
Open waters = lower albedo = absorbs more solar radiation = warming feedback loop
^Ice melts in a matter of centuries
START OF THE GREAT THAW !
Stage 4
Tropical oceans flow
Seawater evaporates = more H2O in the atmosphere = increased greenhouse effect
^Surface temps reach 50 degrees Celsius = feedback loop of evaporation and incrased rainfall
Formation of carbonate sediment (rain erodes rock, rivers wash eroded debris into oceans, carbonate sediment forms)
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golbal climate returns to 'normal'
Formation of the Snowball Earth Model
1960s
Plate tectonics as a model was accepted
Continents had clustered together near the equator (during the neoproterozoic (magnetic orientation data)
Albedo of ice/snow > Albedo of seawater
More radiation reflected = cooler planet (Feedback loop leading to growth of ice)
Climate simulations revealed that this feedback loop can run out of control
Would this 'catastrophe' have not extinguished all life though?
Would this glaciation not have been permanent
1970s
Discovery of extremophiles: organisms that thrive in extreme conditions such as seafloor hotsprings, extreme cold, extreme pH...
Increased survival prospects during the massive glaciation (especially for psychrophilic organisms & organisms near volcanic hot springs)
Volcanic activity = emits CO2= increased greenhouse effect
During glaciation, no flowing water available to sequester this CO2
Resolving the Paradoxes (Using Snowball Earth)
(I) Following the ice age, the great thaw caused glacial debris to form (as explained by stage 3) near the tropics as that is where the thaw started
(II) During the ice age, the oceans were isolated from the atmosphere (less oceanic O2) which allowed Fe to dissolve in the oceans, later to be deposited during the thaw
(III)
See Stage 4
(IV)
See Stage 2
Evidence for Snowball Earth Model
Namibia's Skeleton coast
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Evidence of glacial rock deposits (calcium and magnesium carbonate materials) that life above glacial debris
They hold chemical evidence (Ratios of Carbon-12 to Carbon-13) for the great melting that followed the ice age
These rocks are found on almost every continent
These chemical traces provide evidence for cycles of biological activity
