what actually causes the rotation of the earth on its axis?

Answer 1

Momentum left over from formation of the planets and other parts of the solar system - everything is rotating.

Answer 2

The earth formed by the continual accumulation of debris in the early solar system. As the mass of material accumulated, so did the gravity, drawing in material from ever increasing distances. This then struck the planet with increasing force. The rotation was then the sum of all the impacts. A couple hundred million years after the earth formed, another planet the size of mars collided with it. The force of this enormous impact melted the crust and ejected much of it into space. It then condenced to form the moon. The impact also tilted the axis of rotation. This is why the earth has seasons and the oceans experience tides.

Answer 3

When something moves, if left alone, it will move in a straight line at constant speed. This idea is called inertia.

If something spins about it's axis, if left alone, will continue to spin about it's axis at a constant rate of rotation. This idea is called rotational inertia.

These ideas are so basic to physics that there really isn't a more basic idea that's a cause. It is, however, on equal footing with some symmetries.

According to Noether's theorem, if the laws of physics are the same if you move from one place to another, then you have something called conservation of momentum. Conservation of momentum is roughly the same idea as inertia. If the laws of physics are the same under rotation, then you have something called conservation of angular momentum.

But as far as I know, there is nothing more fundamental that can then "explain" inertia or rotational inertia, so if we take it as given that the Earth at one point was rotating and left pretty much to itself, then the Earth will continue to rotate because of rotational inertia.

Answer 4

There's a big spike through the middle of the earth and a huge pre-teen kid in outer space spinning us and laughing.