Trenches, Ridges, and Plate Tectonics: Exploring Earth's Geology

Trenches:

A narrow, deep depression in the sea floor.

Ridges:

A long narrow hilltop mountain range or watershed.

Disagreement with Alfred and Changed Opinion

Wegener's hypothesis was not widely accepted because he could not explain how the continents moved. In the late 1950s and 1960s, scientists were able to put together the evidence and concluded that the continents did drift.

Layers of the Earth

The innermost layer, the core, is mostly iron. The pressure at the inner core is more than a million times that at Earth's surface. The layer outside is the mantle, though it is thought to be solid, it is very hot, near the melting point of the rocks. The crust is the outermost, and therefore best-known, layer of Earth.

Theory of Plate Tectonics

The theory of plate tectonics states that the pieces of Earth's lithosphere are in slow, constant motion.