The layer of the Earth's interior that contains the highest mountains and deepest oceans is the lithosphere.

Here's why:

* Lithosphere: This is the rigid outermost layer of the Earth, composed of the crust and the uppermost part of the mantle. It's broken into tectonic plates that move and interact with each other.

* Mountains: Mountain ranges are formed when tectonic plates collide and push up the crust.

* Oceans: Ocean basins are formed when tectonic plates pull apart, creating areas where the crust is thinner and can sink, forming depressions that fill with water.

Let me know if you'd like more details about the Earth's layers or tectonic plates!