Biology Forums - Study Force

Early in Earth history, the Sun was less luminous, which should have caused Earth to be much colder and all water to
  be frozen. Yet all evidence points to the presence of liquid water on Earth. Give two explanations that could resolve the
  faint young sun paradox. What will be an ideal response?

1. There was a strong greenhouse effect from carbon dioxide, methane and water vapor in
Earths atmosphere that trapped solar radiation, thus keeping the Earth warmer.
2. Earth had a low albedo, and reflected less light back to space. In other words, it absorbed
more light, which kept temperatures high enough that water could not freeze.