Posted May 24th, 2009 in Physics. Tags: Intermediate-Science, No Equations, Physics, Quickie.
According to the standard solar model, the Sun’s brightness steadily increases because helium ash slowly builds up in its core. The introduction of heavier elements like helium forces the Sun to fuse hydrogen faster in order to prevent gravitational collapse, so it shines brighter as it ages. The Sun was ~25% dimmer 4 billion years ago compared to now.
Liquid oceans had already formed 4 billion years ago, so Earth’s temperature must have been above the freezing point of water. A faint young Sun presents a paradox: how could a 25% dimmer Sun warm the Earth enough to develop liquid oceans? (more…)