Snowball Earth

Proterozoic snowball periods

−1000 —

–

−950 —

–

−900 —

–

−850 —

–

−800 —

–

−750 —

–

−700 —

–

−650 —

–

−600 —

–

−550 —

Tonian

Cryogenian

Ediacaran

Sturtian^[1]

Marinoan^[1]

← Gaskiers

(millions of years ago)

Baykonurian

Neoproterozoic era

Snowball Earth

Estimate of Proterozoic glacial periods.^[2]^[1] Dating of pre-Gaskiers glaciations is uncertain. As for the Kaigas, its very existence is doubted by some. The Huronian glaciation, is not shown, there is a lack of any significant evidence for a Snowball Earth during the time period.

The Snowball Earth is a geohistorical hypothesis that proposes during one or more of Earth's icehouse climates, the planet's surface became entirely or nearly entirely frozen with no liquid oceanic or surface water exposed to the atmosphere. The most academically referred period of such global glaciation is believed to have occurred sometime before 650 mya during the Cryogenian period.

Proponents of the hypothesis argue that it best explains sedimentary deposits that are generally believed to be of glacial origin at tropical palaeolatitudes and other enigmatic features in the geological record. Opponents of the hypothesis contest the geological evidence for global glaciation and the geophysical feasibility of an ice- or slush-covered ocean,^[3]^[4] and they emphasize the difficulty of escaping an all-frozen condition. Several unanswered questions remain, including whether Earth was a full snowball or a "slushball" with a thin equatorial band of open (or seasonally open) water. The snowball-Earth episodes are proposed to have occurred before the sudden radiation of multicellular bioforms known as the Cambrian explosion. The most recent snowball episode may have triggered the evolution of multicellularity.

^ ^a ^b ^c Cite error: The named reference Pu was invoked but never defined (see the help page).
^ Smith, A. G. (2009). "Neoproterozoic timescales and stratigraphy". Geological Society, London, Special Publications. 326 (1): 27–54. Bibcode:2009GSLSP.326...27S. doi:10.1144/SP326.2. S2CID 129706604.
^ Kirschvink, J. L. (1992). "Late Proterozoic low-latitude global glaciation: The snowball Earth" (PDF). In Schopf, J. W.; Klein, C. (eds.). The Proterozoic Biosphere: A Multidisciplinary Study. Cambridge University Press. pp. 51–2.
^ Allen, Philip A.; Etienne, James L. (2008). "Sedimentary challenge to Snowball Earth". Nature Geoscience. 1 (12): 817–825. Bibcode:2008NatGe...1..817A. doi:10.1038/ngeo355.

[Pu-1] Cite error: The named reference Pu was invoked but never defined (see the help page).

[Smith2009-2] Smith, A. G. (2009). "Neoproterozoic timescales and stratigraphy". Geological Society, London, Special Publications. 326 (1): 27–54. Bibcode:2009GSLSP.326...27S. doi:10.1144/SP326.2. S2CID 129706604.

[Kirschvink1992-3] Kirschvink, J. L. (1992). "Late Proterozoic low-latitude global glaciation: The snowball Earth" (PDF). In Schopf, J. W.; Klein, C. (eds.). The Proterozoic Biosphere: A Multidisciplinary Study. Cambridge University Press. pp. 51–2.

[nature_geo-4] Allen, Philip A.; Etienne, James L. (2008). "Sedimentary challenge to Snowball Earth". Nature Geoscience. 1 (12): 817–825. Bibcode:2008NatGe...1..817A. doi:10.1038/ngeo355.

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