Snowball Earth Hypothesis Flashcards
A snowball earth is
“A snowball earth… is a condition where ice-albedo positive feedback ‘runs away’ and the planet becomes covered in snow and ice” (Lenton and Watson, 2013: 270).
Scientists believe there were snowball earth stages when?
Scientists believe that there were two true snowball earth stages during the Neoproterezoic glaciations at 2.2 billion and 700 million years ago.
The ice/albedo feedback
The ice-albedo runaway feedback was suggested by Kirschvink (1992) who proposed that the ocean would be almost completely covered by sea ice, which would convert large areas of oceanic surface with low albedo content into a high albedo land surface. We know that the more reflective the land surface the more sunlight is reflected, so less is absorbed leading to more cooling and more ice advance. Once the ice crosses a critical latitude (about 30 degrees) this leads to a runaway effect creating a snowball earth
Hoffman et al (1998) found
Hoffman et al (1998:1342) found “negative carbon isotope anomalies in carbonate rocks bracketing glacial deposits in Namibia”. Negative carbon isotope anomalies normally marks a time of mass extinction, where there is a decrease in biological productivity. This then provides evidence for the ice crossing the critical latitudes.
Break up of a supercontinent
During the break up phase the continent divides creating a widening ocean from the ridge. On the margins of the ocean weathered material builds up and carbonate rocks can accumulate. Usually, carbonate rocks have the CO2 contained within them released through the means of a volcanic eruption, but without this the weathering sink dominates the tectonic sink leaving less CO2 in the atmosphere (Lenton and Watson, 2013)
Donnadieu et al (2004) found
Donnadieu et al (2004:303) who found via a simulation that “the continental break up of Rodinia leads to an increase in runoff and hence consumption of carbon dioxide through continental weathering that decreases atmospheric carbon dioxide concentrations by 1,320ppm”. It is the reduction of the CO2 in the atmosphere which leads to increased cooling and then the ice-albedo runaway feedback mechanism kicks in
Zipper Rift model
The ‘Zipper-rift’ model proposed by Nick Eyles argues that many of the Neoproterozoic deposits are not glacial at all. The model emphasised the link between the reorganisation of the Earth’s surface through rifting of Rodinia, the climatic effects on the rifted flanks and the sedimentary record left behind. He found that some successions showed a glacial influence but many did not. (Eyles, 2004).
A GMC is
By definition a GMC is “massive clouds of gas in interstellar space composed primarily of hydrogen molecules” (Kumar, 2012)
A, A Pavlov et al (2005) found:
A. A Pavlov et al (2005) who found that interstellar particles from the stratospheric dust layer can trigger the runaway ice-albedo feedback through radiative forcing
Micheels, A and Montenari, M (2008:401) found
evidence to support this ‘slushball’ model. They performed “sensitivity experiments with an earth model… for this period of dramatic global cooling”. They were “able to observe that global climate reacts less sensitively to reductions of atmospheric CO2 during times with increased glaciations” and concluded that their models “support the rather moderate scenario of a slushball earth than the extreme snowball earth hypothesis”.
Hoffman et al (2008: E7) found:
using the “University of Victoria Earth System Climate Model to show that the soft snowball result is only possible when dynamics are excluded from the sea ice component of the model.” The removal of these dynamics leads to a model which is not representative of the earth system as it involves using just a thermodynamic ocean system, rather than the dynamic and thermodynamic regulation of ocean warming that occurs
