The Faint Young sun Paradox

The inability to find more evidence for early glaciation has always stumped scientists because they expected to find evidence supporting abundant glacial events. By studying the evolution of stars in the universe, astronomers have been able to recreate the history of the Sun. The models they have developed indicate that the early Sun was about 30 percent less bright than it is today. These calculations presented a mystery for climatologists, because a decrease of just a few percentage points in the Sun's present strength would cause all the water on Earth to freeze, even with all the CO2 in the air and the greenhouse effect. If all the water in the oceans, lakes, and streams froze today, their high albedo (reflectivity) would make it difficult to melt the ice. What presents such a mystery to scientists is that with such a weak Sun, even if the Earth's greenhouse gas levels were then what they are today, the Earth should have remained completely frozen for the first 3 billion years of its existence. Yet scientists have not been able to find any evidence to support the Earth ever having been completely frozen. Geological evidence for this time has been partly found in sedimentary rocks, and sedimentary rocks are formed from running water, not frozen water. Evidence of a continued presence of life on Earth during this time also does not support the possibility of a planet frozen because of too weak a Sun. This question remains a mystery.

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