Editing Snowball Earth (section)

==History==

===First evidence for ancient glaciation===
Long before the idea of a global glaciation was first proposed, a series of discoveries occurred that accumulated evidence for ancient [[Precambrian]] glaciations. The first of these discoveries was published in 1871 by J. Thomson, who found ancient glacier-reworked material ([[tillite]]) in [[Islay]], Scotland.<ref name="Spencer1971">{{cite book | url=https://doi.org/10.1144/GSL.MEM.1971.006.01.01 | title=Late Precambrian Glaciation in Scotland | publisher=[[Geological Society of London]] | author=Spencer, A.M. | date=1971 | page=2| doi=10.1144/GSL.MEM.1971.006.01.01 }}</ref> Similar findings followed in Australia (1884) and India (1887). A fourth and very illustrative finding, which came to be known as "[[Reusch's Moraine]]," was reported by [[Hans Henrik Reusch|Hans Reusch]] in northern Norway in 1891. Many other findings followed, but their understanding was hampered by the rejection (at the time) of [[continental drift]].<ref name=Hoffman2011>{{cite book |last1=Hoffman |first1=Paul F.|author-link=Paul F. Hoffman|editor-last=Arnaud|editor-first=E. |editor-last2=Halverson|editor-first2=G.P.|editor-last3=Shields-Zhou|editor-first3=G. |year=2011 |title=The Geological Record of Neoproterozoic Glaciations |chapter=A history of Neoproterozoic glacial geology, 1871–1997 |issue=36 |pages=17–37 |series=Geological Society, London, Memoirs|publisher=Geological Society of London}}</ref>

===Global glaciation proposed===
[[Douglas Mawson]], an Australian [[geologist]] and Antarctic explorer, spent much of his career studying the [[stratigraphy]] of the [[Neoproterozoic]] in South Australia, where he identified thick and extensive glacial sediments. As a result, late in his career, he speculated about the possibility of global glaciation.<ref name="Mawson">{{Cite journal | last1 = Alderman | first1 = A. R. | last2 = Tilley | first2 = C. E. | doi = 10.1098/rsbm.1960.0011 | title = Douglas Mawson 1882-1958 | journal = [[Biographical Memoirs of Fellows of the Royal Society]] | volume = 5 | pages = 119–127 | year = 1960 | title-link = Douglas Mawson | doi-access = free }}</ref>

Mawson's ideas of global glaciation, however, were based on the mistaken assumption that the geographic position of Australia, and those of other continents where low-[[latitude]] glacial deposits are found, have remained constant through time.{{fact|date=July 2023}} With the advancement of the continental drift hypothesis, and eventually [[Plate tectonics|plate tectonic]] theory, came an easier explanation for the glaciogenic sediments—they were deposited at a time when the continents were at higher latitudes.

In 1964, the idea of global-scale glaciation reemerged when [[W. Brian Harland]] published a paper in which he presented [[Paleomagnetism|palaeomagnetic]] data showing that glacial tillites in [[Svalbard]] and [[Greenland]] were deposited at [[Tropics|tropical]] latitudes.<ref name="Harland">{{cite journal
| author=W. B. Harland
| title=Critical evidence for a great infra-Cambrian glaciation
| journal=[[International Journal of Earth Sciences]]
| year=1964
| volume=54
| issue=1
| pages=45–61
| bibcode=1964GeoRu..54...45H
| doi=10.1007/BF01821169| s2cid=128676272
}}</ref> From this data and the sedimentological evidence that the glacial sediments interrupt successions of rocks commonly associated with tropical to temperate latitudes, he argued that an [[ice age]] occurred that was so extreme that it resulted in marine glacial rocks being deposited in the tropics.

In the 1960s, [[Mikhail Budyko]], a Soviet climatologist, developed a simple energy-balance climate model to investigate the effect of ice cover on global climate. Using this model, Budyko found that if ice sheets advanced far enough out of the polar regions, a [[Feedback|feedback loop]] ensued where the increased reflectiveness ([[albedo]]) of the ice led to further cooling and the formation of more ice, until the entire Earth was covered in ice and stabilized in a new ice-covered equilibrium.<ref name="Budyko">{{cite journal
| author=M.I. Budyko
| title=The effect of solar radiation variations on the climate of the Earth
| journal=[[Tellus A]]
| year=1969
| volume=21
| issue=5
| pages=611–619
| doi=10.3402/tellusa.v21i5.10109
| bibcode=1969Tell...21..611B
| doi-access=free
}}</ref> While Budyko's model showed that this ice-albedo stability could happen, he concluded that it had, in fact, never happened, as his model offered no way to escape from such a feedback loop.

In 1971, Aron Faegre, an American physicist, showed that a similar energy-balance model predicted three stable global climates, one of which was snowball Earth.<ref name="Faegre">{{cite journal
| author=A. Faegre
| title=An Intransitive Model of the Earth-Atmosphere-Ocean System
| journal=[[Journal of Applied Meteorology]]
| year=1972
| volume=11
| issue=1
| pages=4–6
| doi=10.1175/1520-0450(1972)011<0004:AIMOTE>2.0.CO;2
| bibcode=1972JApMe..11....4F
| doi-access=free
}}</ref> This model introduced [[Edward Norton Lorenz]]'s concept of [[intransitivity]], indicating that there could be a major jump from one climate to another, including to snowball Earth.

The term "snowball Earth" was coined by [[Joseph Kirschvink]] in a short paper published in 1992 within a lengthy volume concerning the biology of the [[Proterozoic]] eon.<ref name="Kirschvink" /> The major contributions from this work were: (1) the recognition that the presence of [[banded iron formation]]s is consistent with such a global glacial episode, and (2) the introduction of a mechanism by which to escape from a completely ice-covered Earth—specifically, the accumulation of [[Carbon dioxide|CO<sub>2</sub>]] from [[Volcano|volcanic outgassing]] leading to an ultra-[[greenhouse effect]].

Franklyn Van Houten's discovery of a consistent geological pattern in which lake levels rose and fell is now known as the "Van Houten cycle". His studies of [[phosphorus]] deposits and banded iron formations in [[Sedimentary rock|sedimentary rocks]] made him an early adherent of the snowball Earth hypothesis postulating that the planet's surface froze more than 650 Ma.<ref>{{cite web| url = http://www.princeton.edu/main/news/archive/S28/44/69O99/index.xml?section=topstories| title = Princeton University - Franklyn Van Houten, expert on sedimentary rocks, dies at 96}}</ref>

Interest in the notion of a snowball Earth increased dramatically after [[Paul F. Hoffman]] and his co-workers applied Kirschvink's ideas to a succession of Neoproterozoic sedimentary rocks in [[Namibia]] and elaborated upon the hypothesis in the journal ''[[Science (journal)|Science]]'' in 1998 by incorporating such observations as the occurrence of [[cap carbonate]]s.<ref name="Hoffman">{{Cite journal
| last3=Halverson
| first1=P. F.
| first2=A. J.
| last2=Kaufman
| first3=G. P.
| first4=D. P.
| last1=Hoffman 
| title = A Neoproterozoic Snowball Earth
| last4=Schrag
| journal = [[Science (journal)|Science]]
| volume = 281 
| issue=5381
| pages = 1342–1346
| year = 1998
| doi = 10.1126/science.281.5381.1342
| pmid=9721097
| bibcode = 1998Sci...281.1342H
| s2cid=13046760
| url=https://semanticscholar.org/paper/37b1ffb6aadc8b436c029fb8a3311c0b26e30d4e
}}</ref>

In 2010, Francis A. Macdonald, assistant professor at [[Harvard University|Harvard]] in the Department of Earth and Planetary Sciences, and others, reported evidence that [[Rodinia]] was at equatorial latitude during the [[Cryogenian]] period with glacial ice at or below sea level, and that the associated [[Sturtian glaciation]] was global.<ref>{{cite journal |last1=Macdonald |first1=F. A. |last2=Schmitz |first2=M. D. |last3=Crowley |first3=J. L. |last4=Roots |first4=C. F. |last5=Jones |first5=D. S. |last6=Maloof |first6=A. C. |last7=Strauss |first7=J. V. |last8=Cohen |first8=P. A. |last9=Johnston |first9=D. T. |last10=Schrag |first10=D. P. |title=Calibrating the Cryogenian |journal=Science |date=4 March 2010 |volume=327 |issue=5970 |pages=1241–1243 |doi=10.1126/science.1183325 |pmid=20203045 |bibcode=2010Sci...327.1241M |s2cid=40959063}}
*{{cite press release |date=5 March 2010 |title=Snowball Earth: New evidence hints at global glaciation 716.5 million years ago |website=ScienceDaily |url=https://www.sciencedaily.com/releases/2010/03/100304142228.htm}}</ref>