The Faint Young Sun
This amazing photo shows Atlantis and ISS silhouetted against the Sun.
The "Faint Young Sun" has long been a paradox. Astrophysicists have developed detailed models of the Sun's evolution. According to these models life should not have evolved on Earth, because 4 billion years ago the Sun shone with barely 70% of its present luminosity. Earth's temperature would have been 15 degrees below zero centigrade and the planet woud have been frozen solid. Evolution of life would have been very unlikely.
Geology shows evidence of sedimentation 4 billion years ago, indicating presence of rivers and seas. Other geological markers confirm the presence of liquid water. Paleontology dates the earliest organisms at least 3.4 billion and possibly 4 billion years old. Clearly water and life both existed when models say that Earth was frozen solid. The fact that life exists to read this post contradicts the standard solar model. This conflict with observations is the Faint Young Sun Paradox.