Explain why ancient rocks are not found on the seafloor?

Answer 1

It depends on what you call ancient. The oldest oceanic crust is located near Siberia in the northwest part of the Pacific Ocean. These rocks are about 180 million years old. To me, that is "ancient". Compared to the oldest continental crust, which is about 3 billion years old, they are babies. Oceanic crust is denser than continental crust, and when there is an oceanic crust/continental crust collision, most of the oceanic crust is subducted beneath the continent. Ophiolites are the exception where oceanic crust is obducted (if there is such a word) onto the continental crust. But even here continental crust is not subducted down to the mantle.

Answer 2

Ancient rocks on the seafloor have been subducted beneath continental masses. Hence nowhere are there rocks older than the late Paleozoic Era on the seafloor.

Answer 3

I would think that if you go deep into the Mariana trench you would find ancient rocks. However, because much of the deep ocean rifts are volcanic in nature, the seascape is in a constant state of change. Certainly the Hawaiian Islands that arose out of the seabed are hundreds of millions of years old, and a new Hawaiian island will break the water's surface in another 10 million years. Where there is no volcanic activity, but instead a river carving deeper and deeper into mainland rock, you do find ancient rocks, like those at the bottom of the Grand Canyon, named Vishnu Schist, which is estimated to be 2 billion years old, which I guess is considered ancient.

Answer 4

The oldest ocean floor is Jurassic, which is quite old, but not as old as the cores of continents. The reason, as others have said, is that new crust is created at spreading ridges and older crust is subducted in subduction zones. As ocean crust moves away from the spreading ridges, it gets older, colder, and denser. Then it starts to sink (new subduction zones). So, there are actual physical limitations to how old ocean crust can be. Continental crust, which has a different composition, is buoyant and doesn't easily subduct. Therefore, really old material is preserved.

Answer 5

Seafloor spreading. The seafloor is young.

Answer 6

errosion?