Crust, the upper layer of the Earth, is not always the same. Crust under the oceans is only about 5 km thick while continental crust can be up to 65 km thick. Also, ocean crust is made of denser minerals than continental crust. read more
Generally speaking, the crust of the earth is a solid. Yes, there are oceans on the earth. Heck, they cover much of the surface. But the crust extends down well below the bottom of the ocean. Earth's crust is up to 70 kilometers deep, which is over 40 miles. The deepest the ocean gets is roughly 7 miles. read more