A thick haze of organic material let the early Earth soak up the sun's warmth without absorbing harmful ultraviolet rays, according to a new study.

The model offers a new twist on an old puzzle: Although the sun was so dim billions of years ago that the Earth should have been a ball of ice, the young planet had liquid oceans capable of supporting life.

"Given these recent papers, we can probably say the early faint sun problem is not one of the problems anymore in solving the origin of life," said astrophysicist Christopher Chyba of Princeton University, who was not involved in the new work.

The sun should have been up to 30 percent less bright 3.8 billion to 2.5 billion years ago, according to studies of the lifecycles of sun-like stars. If the Earth's atmosphere had the same composition then as it does now, it would have frozen over completely, like Jupiter's moon Europa. But geological records show the Earth was at least as warm and wet then as it is today.

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