Scientists have found the cause of global glaciation
Global ice ages in Earth's history occurred when the level of solar radiation is sharply changed in a short period by geological standards the period of time, American scientists have found. Their work was published in the journal Proceedings of the Royal Society A.
In Earth's history was at least two periods of the Paleoproterozoic 2.4 to 2.1 billion years ago during the Neoproterozoic 850-630 million years ago, when the whole surface of the planet was covered with ice. With the end of the second period of time is associated sudden flowering of complex multicellular life on Earth. Therefore, not only geologists and planetary scientists studying exoplanets lying within the habitable zones, looking for the causes that can trigger a global glaciation.
Scientists from mit have considered several scenarios in which the main drivers universal cooling have considered the levels of incoming solar light and carbon dioxide in the atmosphere.
The planet has its own internal mechanisms of regulation of these parameters, therefore, according to the researchers, to overcome the critical threshold of any of them, events must happen very fast, that is the most important factor is the pace of climate change.
The authors believe that the sharp decline in solar radiation reaching the surface, could be related to mass eruption of volcanoes or formation of biologically induced cloud that blocks the sunlight. And in that and in other case the cooling of the planet and the expansion of the ice.
Then generated a positive feedback: the more ice, the more albedo — the reflectivity of the Earth's surface, the more sunlight is reflected without heating the planet. The cooling process is accelerated as long as the ice does not cover the entire planet.
But any global ice ages on Earth are temporary because of the existence of the carbon cycle. When the planet is not covered with ice, carbon dioxide levels in the atmosphere to some extent controlled by the weathering of rocks. When the planet is covered with ice, weathering is much reduced and the carbon dioxide accumulates in the atmosphere, creating a greenhouse effect, which ultimately removes the planet from the ice age.
The researchers developed a simple mathematical model of Earth's climate system, which includes the equations of the relations between incoming and outgoing solar radiation, surface temperature, concentration of carbon dioxide in the atmosphere and the effects of weathering.
It turned out that for the transformation of the planet to "snowball" the rate of reduction of incoming solar radiation is a more important parameter than the size of the stream. According to the authors, the Earth should experience approximately a two percent drop in incoming sunlight for ten thousand years to return to a global glacial period.
Scientists think that their findings can be extended to exoplanets, located in a potentially habitable zone. They can also be icy if will sharply decrease the level of incoming to the surface radiation from the star.
"You can have a planet that is within the classical habitable zone, but if the incoming sunlight is changing too fast, you can get the planet-"snowball" — are in the press release of the Institute the words of the first author of the study Arnside Konstantin (Constantin Arnscheidt), graduate student of the faculty of Earth Sciences, atmosphere and planets. — This indicates that the concept of habitability is much more nuanced".
According to the authors, the formation of the snow planets depends on the balance between incoming solar light, feedback of ice albedo and the global carbon cycle. The researchers plan to continue their research to determine the critical values for each of these parameters.