The "young sun paradox" just won't go away. For decades, scientists like Carl Sagan have tried to resolve this mystery of the early solar system—how the newborn Earth stayed warm enough to keep liquid water—but it continues to bob and weave around an answer. In the journal Nature, a team led by Minik Rosing proposes an alternate solution to the leading theory, which relies on the greenhouse effect hypothesis. But don't expect the debate to end here. The problem is this: The young Earth received much less heat from the sun. Four billion years ago,
a lower solar luminosity should have left Earth's oceans frozen over, but there is ample evidence in the Earth's geological record that there was liquid water — and life — on the planet at the time [Space.com]
. So what gives? The traditional explanation going back to the 1970s has been that a powerful greenhouse ...
