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These days the climate news is all about global warming, but global freezing was the biggest climate worry in Earth's distant past.
Long periods of severe cold - like Ice Ages on steroids - brought glaciers down to the equator and froze much if not all of the oceans. Scientists still debate what triggered these so-called Snowball Earths, but equally uncertain is how the Earth unfroze itself. One research group is studying the hyper-greenhouse warming that would be needed to end a million-year-long winter.
The evidence for Snowball Earths comes from paleomagnetic data taken from ancient glacial deposits. From their magnetic properties, geologists can tell that some of these ice-induced rocks originated from low latitudes. This surprising result implies a cold planet that only would get colder as the ice reflected away more heat.

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New Evidence Supports Snowball Earth as Trigger for Early Animal Evolution

Biogeochemists have found new evidence linking "Snowball Earth" glacial events to the rise of early animals. The research was funded by the National Science Foundation (NSF).
Study results appear in this week's issue of the journal Nature.
The controversial Snowball Earth hypothesis posits that, on several occasions, the Earth was covered from pole to pole by a thick sheet of ice lasting for millions of years.
These glaciations, the most severe in Earth history, occurred from 750 to 580 million years ago.
In the aftermath, the researchers discovered, the oceans were rich in phosphorus, a nutrient that controls the abundance of life in the oceans.

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Title: Archean Paleo-climate: The first snowball?
Authors: Hector Javier Durand-Manterola
(Version v2)

The model accepted is one where during the Archean Eon the Earths climate was clement despite the weaker Sun. The observational evidence that supports this concept is: the emergence of life, the existence of evaporitic sediments and the presence of terrigenous sediments, all of which require liquid water and clement conditions. A theoretical argument used to support this idea is the so called ice-albedo feedback, which states that if the Earth was frozen, it would still be frozen.The aim of this document is to present an alternative scenario in which a frozen world, "snowball" style, with liquid water at the bottom of the sea, also allows for the emergence of life and evaporitic and terrigenous sedimentation. Archean climatic evidence, available at present, is discussed and can be reinterpreted to support the idea that, in Archean times, the surface of the Earth was frozen. Also, a mathematical model is being developed to demonstrate that the ice-albedo feedback is not an inevitable consequence of a frozen Archean Eon. Results: Reinterpretation of the evidence shows that life could appear within the oceanic depths and not necessarily on the surface. The evaporitic sediments could have formed by saline saturation of the water enclosed in the limited cavities of liquid water located at the bottom of the ocean. Also, the terrigenous sediments could have been formed by catastrophic currents of liquid water due to the fusion of the ice from the sub glacial volcanoes. From the mathematical model it is deduced that the defrosting moment of the Earth is towards the end of the Proterozoic, moment in which the evidence shows the "snowball" Earth ends.

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Global glaciation snowballed into giant change in carbon cycle

For insight into what can happen when the Earth's carbon cycle is altered -- a cause and consequence of climate change -- scientists can look to an event that occurred some 720 million years ago.
New data from a Princeton University-led team of geologists suggest that an episode called "snowball Earth," which may have covered the continents and oceans in a thick sheet of ice, produced a dramatic change in the carbon cycle. This change in the carbon cycle, in turn, may have triggered future ice ages.
Pinpointing the causes and effects of the extreme shift in the way carbon moved through the oceans, the biosphere and the atmosphere -- the magnitude of which has not been observed at any other time in Earth history -- is important for understanding just how much Earth's climate can change and how the planet responds to such disturbances.
Publishing their findings in the April 30 issue of the journal Science, the researchers also put forth a hypothesis to explain how changes to Earth's surface wrought by the glaciers of the Neoproterozoic Era could have created the anomaly in carbon cycling.

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Scientists Find Signs of "Snowball Earth" Amidst Early Animal Evolution

Geologists have found evidence that sea ice extended to the equator 716.5 million years ago, bringing new precision to a "snowball Earth" event long suspected to have taken place around that time.
Funded by the National Science Foundation (NSF) and led by scientists at Harvard University, the team reports on its work this week in the journal Science.
The new findings--based on an analysis of ancient tropical rocks that are now found in remote northwestern Canada--bolster the theory that our planet has, at times in the past, been ice-covered at all latitudes.

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Focusing on a controversial hypothesis that ice existed at the equator some 300 million years ago during the late Palaeozoic Period, two University of Oklahoma researchers originated a project in search of clues to the Earth's climate system.

"The Palaeozoic Period was a rare time in history. Broadly speaking, it was the last time our planet experienced the type of climate system we have today and in the recent past" - Gerilyn Soreghan, OU professor of geology.

Soreghan believes comparing more modern systems in a range of different climates might help support her hypothesis.
Soreghan and Elwood Madden, assistant professor of geochemistry, want to search for answers in four distinct environments: the cold-dry environment found in Antarctica, the cold-wet environment found in Norway, the hot-wet environment found in Puerto Rico and the hot-dry environment found in the Mojave Desert.

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A 250-million-year shutdown of volcanic activity which is thought to have occurred early in Earth's history may be what turned the planet into a glacier-covered snowball. It could also have helped give rise to our oxygen-rich atmosphere.
Previous studies have noted that very little volcanic material has been dated to between 2.45 and 2.2 billion years ago, but it was widely assumed the gap would vanish as more samples were dated. Now an analysis of thousands of zircon minerals collected from all seven continents indicates that the gap may be real after all. Zircons provide a record of past volcanic activity, as the date they were formed can be calculated from the radioactive isotopes they contain.

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The planets present day greenhouse scourge, carbon dioxide, may have played a vital role in helping ancient Earth to escape from complete glaciation, say scientists in a paper published online today.
In their review for Nature Geoscience, UK scientists claim that the Earth never froze over completely during the Cryogenian Period, about 840 to 635 million years ago.
This is contrary to the Snowball Earth hypothesis, which envisages a fully frozen Earth that was locked in ice for many millions of years as a result of a runaway chain reaction that caused the planet to cool.
What enabled the Earth to escape from a complete freeze is not certain, but the UK scientists in their review point to recent research carried out at the University of Toronto. This speculates that the advancing ice was stalled by the interaction of the physical climate system and the carbon cycle of the ocean, with carbon dioxide playing a key role in insulating the planet.

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Earth survived extreme climate change approximately 750-550 million years ago, before dinosaurs roamed our planet.
During this time, the Earth was alternately subjected to the most severe ice age conditions it ever witnessed (with ice present even around the Equator), and then to widespread tropical greenhouse conditions, according to researchers.

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