The angular momentum of an object is defined as the product of its mass, its velocity, and its distance from the axis of rotation. In the case of the Earth, the mass is very large, the velocity is relatively small, and the distance from the axis of rotation is also large. This means that the Earth has a very large angular momentum.
The tidal forces exerted by the Moon and Sun cause the Earth to bulge out slightly on the side facing them. This creates a slight asymmetry in the Earth's mass distribution, which causes the Earth to wobble slightly on its axis. This wobbling motion is called precession.
Precession causes the Earth's axis of rotation to slowly move over time. This means that the Earth's angular momentum is not constant, but rather it is gradually decreasing. However, the rate of decrease is very small, and the Earth's angular momentum is still very large.
