The Earth's Constant Drift
(This is a contribution from a reader. The webmaster's answer is at the bottom of the page.)
The Earth is moving very, very slowly away from the Sun. This happens for two reasons. The first is that the Sun is constantly losing mass because of the solar wind. As the mass of the Sun decreases its pull on the Earth decreases and so the Earth moves slightly further away. The second reason is to do with tidal forces. In exactly the same way that the Moon is slowly moving away from the Earth, the Earth is very slowly moving away from the Sun. In the Earth-Moon case the Moon pulls on the Earth creating tides and slowing the Earth's rotation very slightly, making the day longer. This action has a reaction - the Moon's orbit is speeded up. If something travels faster it must move outwards to remain in an orbit and so the Moon slowly drifts away from us at a rate of 3.8 centimetres per year. The same situation happens with the Sun but the Earth's influence on the Sun is much smaller than the Moon's influence on the Earth. The result is the Earth's tiny, tiny drift away from the Sun.
Now imagine if the earth were as old as some people believe it is. The earth could not survive because of how close it would to the sun. Over a time period of thousands of years this small drift has not made that big of a distance. But over billions of years the earth would have been so close it would have been incinerated.