Snowball Earth

There was a period, about 650 million years ago, or in Precambiano (Cryogeniano, Neoproterozoic), when life on Earth was still only unicellular and resided in the oceans, our planet went to meet an ice age scale planetary. In practice, the entire globe was covered for 25 million years by a mantle of ice several kilometers thick. According to one of the biggest supporters of this theory, the American scholar Joseph L. Kirschvink, there were four episodes of this type occurred between 590 and 900 million years ago, and one of the most remote, about two billion years ago.
From what we know the Earth encounters every one hundred thousand years for reasons mostly of astronomical alignment, a glaciation of varying degrees, but never the ice was pushed to the equator (although with a thickness of only 3 meters due to flattening at the poles the planet) that completely covers the entire surface of the Earth. In these extreme conditions, every niche, every habitat, every place on Earth was completely buried by ice and made completely inhospitable to life. This cataclysm wiped out almost all forms of microscopic life that had hitherto with difficulty evolved on the planet 4 billion years after its formation, the risk of a mass extinction sterilize the global biological destiny of the Earth and therefore each possible resumption of life as we know it, as it fortunately did not go well and we are here to tell the tale.
The causes of this exceptional event are due mainly to two factors: the weathering and the action of cyanobacteria.
The first is a weather event that occurs under particular conditions, or in the presence of a persistent hot-humid environment where the rains subtract carbon dioxide to the atmosphere. Such an environment was created, because at that time the continental drift had piled them all together at the equator in one large supercontinent called Rodinia, as demonstrated by the findings of geological rocks dragged by the mighty glaciers. High humidity tore therefore the CO2 from the atmosphere, making it precipitate in the oceans, which probably went to add the ability of effusive basalts, then abundant as a result of the formation of Rodinia, who by their porosity contributed to pushing the oceans absorb CO2 to subtract compensation for the same atmosphere. The decreased concentration of this molecule in the atmosphere, the greenhouse which we know holds some of the heat of the sun warming the planet, has meant that the temperature calasse in a short time of several degrees below zero, due to the effect of positive feedback due to the same advancing ice, which, by reflecting sunlight, further accelerated the cooling of the planet.
But the CO2 cycle was compromised not only by exceptional weathering, but also aggravated by the action of cyanobacteria, which already existed in the primordial ocean from 3 billion years. As we had access to the CO2 that fell on the seabed imprisoned with their metabolism in the structures of calcareous stromatolites created by them, immense barriers similar to those existing reefs, spread on a global scale. So locked into a sediment irreversible, the CO2 was finally removed from the atmosphere, causing the greenhouse effect and the sharp drop in temperature, which led in a short time the ice to cover the entire globe. The Earth went well at the meeting point of no return, with an ice age that lasted for a period of no less than 25 million years.
The life risked total extinction and the impossibility of being able to evolve into multicellular aggregates and forms more complex, if not disappear forever as has happened on Mars and Venus. If we think about it, life really is such a rare and delicate, given how many factors required to take root and grow (at least as we know it) that perhaps the Universe can only occur due to its vastness, as a matter of purely probabilistic.
However, the life, if he got to svillupparsi in many different forms (and so it was for the bacteria that then populated the ocean) and some probably possess in their genetic capacity to resist and adapt to change, and so it is state. Although about 99% of the biodiversity of bacteria became extinct from the planet is not overwhelmed by the grip of frost, some species were able to survive and adapt, species that now call estremofile. The ice cap covered the land and oceans to kilometers thick, but inevitably remained ravines, caves, cliffs, crevices, where sheltered from the wind, sun and extreme cold, some bacteria, conglomerates of dust on the walls or ice or rock remained free from it, or at the hot springs underwater, or even near the equator where conditions were more favorable, perhaps, hardly survived by adapting their metabolism with the environment offered them. So it was that, at the end of the period "snowball Earth" (snowball Earth, as the Americans like to call it), since these bacteria survived, evolved, when the ice retreated and returned to liquid oceans, all forms of life we know today, following the evolutionary path that subsequent events traced for them.
The never-ending ice age came to an end thanks to two events due to the same phenomenon: the volcanism. Thousands of volcanoes called into motion by the drift of the continental plates that once again resumed to migrate due to mantle convection, broke up from beneath kilometers of ice (and we know that it is possible as we have seen today on a local scale) the thick icy crust, in many events point perhaps insignificant when viewed from space, compared to a planet entirely ice cream, but most were below the heat emissions from each volcano of billions of tons of carbon dioxide that poured into the atmosphere, he went to compensate for the lack than subtracted from weathering and cyanobacteria 25 years before millions of tourists. So it was that, thanks to the dynamism of life always active on this planet (which we can not say of Mars) the greenhouse effect that ensued held much solar heat long enough because in head to one million years, the ice broke up, retreating towards the poles. At that point, life returned, evolved in bacteria capable of releasing oxygen, poisoning the atmosphere and all forms of life are unable to use it, relegating them to more and more extreme environments, and these new photosynthetic organisms evolved the first forms of life multicellular and from them in an explosion of adaptive radiation, the entire biomass paleontology reveals that, up to the present forms, including us humans that we are discovering, after more than half a billion years, this tragic event which, apparently, we owe our existence.

an article by Cristiano Cascioli