What is the reason abt Earth's rotation?

Answer 1

One theory suggests, about 4.6 billion years ago a nearby star was destroyed in a supernova and the explosion sent a shock wave through the solar nebula, causing it to gain angular momentum.
As the cloud began to accelerate its rotation, gravity and inertia flattened it into a protoplanetary disk oriented perpendicularly to its axis of rotation. Most of the mass concentrated in the middle and began to heat up, but small perturbations due to collisions and the angular momentum of other large debris created the means by which protoplanets began to form.

Answer 2

According to the theory of conservation of angular momentum,the revolution(about the sun) and rotation of the earth must have originated at the time it formed from a rotating gaseous nebula.Rotation in the same sence as the revolution should have been the natural dynamical motion where no or least resistance can be encountered.As there is no resistanse due to friction in the space the earth continues to spin.

Answer 3

The Earth and the rest of our solar system was formed within a dense cloud of gases and dust (..called a 'nebula'..) That cloud had motions and movement, just like any cloud you see in our sky. As each body of the solar system formed, including Earth, it borrowed some of that motion and movement. Putting it into fancy words, that's called the Law of Conservation of Momentum