What is the bases of scientist in deviding earth's lithosphere into several plates?

Answer 1

According to the theory of plate tectonics, the Earth's crust and upper mantle are broken into moving plates. The lithospheric plates are solid rock. There are several very large plates, each consisting of both oceanic and continental portions. There are a dozen or more smaller plates. The plates average about 80 kilometers (50 miles) in thickness. All of the plates are moving. They are slow, moving at speeds of centimeters to tens of centimeters per year. They slide along on top of an underlying mantle layer called the asthenosphere, which is composed of a rock that is fluid-like.

Geologists have distinguished three main internal subdivisions of the Earth, based on the behavior of seismic waves and laboratory experiments. The outermost layer is the crust. Underlying the crust is the second layer, the mantle. It comprises the largest portion of the Earth. Like the crust, it is also composed of silicate minerals. The innermost portion of the Earth is the core. It is composed of metallic elements, primarily iron and nickel. The core is subdivided into two parts. The outer core is liquid metal, while the inner core is solid.