Snowball Vs Slushball Earth

Question 1

Snowball def

Answer 1

Earths oceans and land surfaces were covered by ice from the poles to the equator during at least 2 extreme cooling events during the Proterozoic Eon (Brittanica, 2024)

Question 2

Slushball def

Answer 2

Counter theory, only partially covered in ice, massive ice sheets but some only thin watery layer, Cowen’s ‘history of life’

Question 3

Similarities - Global Glaciation Events

Answer 3

-both propose glaciation in the Proterozoic Eon (around 700mya)
-evidence in glacial deposits worldwide, geochronology on quartz veins allowing dating of these glaciation events (Courtney-Davis, 2024)
-Both suggest this cooling is attributed to changes in atmo C02 and less solar luminosity (Voigt et al, 2011)

Question 4

Similarities - CO2 feedback loops + Biological implications

Answer 4

-Both involve the role of C02 buildup from volcanism to end the glaciations “runaway greenhouse effect”
-Both acknowledge survival of microorganisms/extremophiles

Question 5

Similarities - ice-albedo feedback

Answer 5

-Both involve this mechanism, increased cover - increased reflectivity - further cooling - perpetuating glaciation (Voigt et al, 2011)

Question 6

Differences - extent of ice cover

Answer 6

Snow - entire planet including the equator
Slush - equatorial = partially ice-free or thinly covered, liquid water

Question 7

Differences - Habitability

Answer 7

Snow- extreme, life in isolated refugia (hydrothermal vents, sub glacial lakes), prokaryotic organisms like bacteria (Hoffman, 2002)
Slush- greater biological activity, photosynthesis available = organisms can survive, Cowen’s History of life

Question 8

Differences - Climate

Answer 8

Snow- temp can be below -45, -70 at the poles (Micheels and Montenari, 2008)
Slush- ocean currents + equatorial heat transport = prevent freezing, poles -50, some equatorial regions remain above freezing

Question 9

Differences - Geological records

Answer 9

Snow- widespread evidence glacial deposits at equator/tropical latitudes
Slush- suggests that some have been misinterpreted

Question 10

Big conc

Answer 10

Snow- lessons on extreme climate feedbacks, Slush - emphasises resilience of climate system
-Agree on extreme glaciation, pretty much disagree on everything else (list)
-Ultimately shows extremity climate has no real extent + need for debate,