The faint young Sun paradox or problem describes the apparent contradiction between observations of liquid water early in the Earth's history and the astrophysical expectation that the Sun's output would be only 70% as intense during that epoch as it is during the modern epoch. The issue was raised by astronomers Carl Sagan and George Mullen in 1972. Explanations of this paradox have taken into account greenhouse effects, astrophysical influences, or a combination of the two.
Read more about Faint Young Sun Paradox: Early Solar Output, Greenhouse Hypothesis, Alternatives
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“The morning comes to consciousness
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With all its muddy feet that press
To early coffee-stands.”
—T.S. (Thomas Stearns)
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—Charles Dickens (1812–1870)
“One would appear ridiculous who would say, that it is only probable the sun will rise to-morrow, or that all men must die; though it is plain we have no further assurance of these facts than what experience affords us.”
—David Hume (1711–1776)
“To make advice agreeable, try paradox or rhyme.”
—Mason Cooley (b. 1927)