Faint young Sun paradox
APPARENT MYSTERY THAT THE EARLY EARTH SEEMS TO HAVE HAD LIQUID WATER, EVEN THOUGH THE YOUNG SUN WAS LESS BRIGHT, THUS PRESUMABLY COMPLETELY FREEZING THE EARTH
Faint Early Sun Paradox; Faint young sun paradox; Faint young Sun problem; Young sun paradox; Faint sun paradox
The faint young Sun paradox or faint young Sun problem describes the apparent contradiction between observations of liquid water early in Earth's history and the astrophysical expectation that the Sun's output would be only 70 percent as intense during that epoch as it is during the modern epoch. The paradox is this: with the young sun's output at only 70 percent of its current output, early Earth would be expected to be completely frozenbut early Earth seems to have had liquid water and supported life.