A biologist whose interest lies primarily in the study of plants or animals can be called a naturalist, although these days it's more likely she'll be called a natural historian, a botanist, or a zoologist.
Older oceanic crust, which is more dense than continental crust, has long since been recycled in the process of subduction. Credit: U.S. Geological Survey. Plate tectonics shapes the surface of our planet, but it also runs much deeper: Plate movement is the surface expression of convection in Earth's interior.