It seems that the Earth there are about 4 billion years, was already covered with liquid water despite the low light of the young Sun.
At the beginning of the creation of the solar system, the young Sun had a low light (70% of its current brightness).
With such a solar luminosity, the total area of the Earth would be frozen.
In the current environmental conditions, the solar output would be insufficient to maintain a liquid ocean. However, geological data indicate a relatively warm Earth's surface, with the exception of a cold phase, there are 2.4 billion years.
The old riddle of the year 1972, raised by the astronomers Carl Sagan and George Mullen, was relaunched as evidence of liquid water and life, in the form of bacteria were found in geological strata, the start of training Earth.
Sagan and Mullen suggested at the time, a greenhouse effect caused by ammonia and methane, would have allowed the earth to keep water in liquid form.
By analyzing a stone age of 3.8 billion years, discovered in Greenland, the team Minik Rosing, a professor at the University of Copenhagen (Denmark), was able to estimate the atmospheric CO2 concentration in the Archean.
This concentration three times higher than today is not enough to offset a less bright sun. | | Danish researchers suggest an alternative explanation, therefore, minimizing the role of greenhouse gases in global warming.
Minik Rosing, think that the Archean Earth's ability to absorb the sun's heat was better.
The ocean surface trap heat better than land and the skies were less cloudy.
The sun's rays could easily reach the surface. These researchers argue instead for a lower albedo, that is to say, the Earth returned less heat into space and store more energy.
We do not know precisely the time when the continents first appeared on Earth or the time required for training.
But scientists assume that the surface of the planet early in its history, there are about 4 billion years ago, was mostly covered with oceans.
Since water absorbs heat better than the rocks and the clouds were, they say, fewer, that is enough to warm the climate and maintain water in liquid form on the planet.
Many hypotheses have been advanced by different researchers but without global consensus.
Despite the explanations of the greenhouse gas emissions, cosmic rays, solar energy higher than expected and the solar wind, the mystery still persists in 2010. | | 
* Drilling from 2008 to Isua, Greenland, allowed to retrieve rocks called "banded iron formation".
These witnesses of the early ages of the planet are seen by the microscope.
Credit: Laboratory for Planetary Studies, Cornell University, Ithaca, New York |
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