text: The Monty Pithon had a song "Money makes the world go round" \n\nBut since the question is in the astronomy category, perhaps you are after the serious answer.  Momentum.  The earth condensed from particles at the beginning of the solar system, and all those small rocks were in orbit around the sun, thus had momentum in them.  By falling into one another, they gave that momentum to the accumulating mass, which started spinning.  Actually, all planets rotate, it is the norm rather than the exception.\n\nBeing in space, without anything substantial to slow it down, save from the moon and sun tidal effect, the earth keeps spinning since then.