Source of Gravity

can you tell me what is the source of earth’s gravity, ie how it came about. Is it due to the rotation of the earth? If so, how does the rotation of the earth lead to the creation of the gravitational field? (please try as much as possible to put the explanation in simple terms =) )
- Anonymous (age 15)

Everything is a source of gravity, for reasons that we ultimately do not understand. The amount of gravity depends on the amount of stuff ("mass", or "energy"). The Earth has a lot of mass so it gives rise to a lot of gravity. The Earth’s spin has some very subtle effects on its gravity, predicted by General Relativity, but I’m not sure that anyone has yet succeeded in measuring these tiny effects.

Mike W.

p.s. Now the Gravity Probe B experiment has succeeded in measuring the tiny frame-dragging effect of the Earth's spin.

(published on 10/22/2007)