Back Sneeubalaarde Afrikaans الأرض كرة ثلج Arabic Snježna grudva Zemlja BS Terra bola de neu Catalan Teorie sněhové koule Czech Sneboldjord Danish Schneeball Erde German Glaciación global Spanish Elur-bola Lurra Basque زمین گوی برفی Persian
Proterozoic snowball periods | ||||||
−1000 — – −950 — – −900 — – −850 — – −800 — – −750 — – −700 — – −650 — – −600 — – −550 — | ← Gaskiers (millions of years ago) | |||||
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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 that during one or more of Earth's icehouse climates, the planet's surface became nearly entirely frozen with no liquid oceanic or surface water exposed to the atmosphere. The most academically mentioned period of such a global ice age is believed to have occurred some time before 650 mya during the Cryogenian period, which included at least two large glacial periods, the Sturtian and Marinoan glaciations.
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 radiations of multicellular bioforms known as the Avalon and Cambrian explosions; the most recent Snowball episode may have triggered the evolution of multicellularity.
- ^ a b c Cite error: The named reference
Puwas 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.