inside earth
There are two ways to slice the Earth’s interior, and they do not line up. One divides by what the layers are made of; the other by how they behave. Plate tectonics happens on the second division.
About: Lithosphere · Asthenosphere · Continental crust · Oceanic crust
Compositionally, the Earth has three main layers: crust, mantle and core.[1]
Mechanically, the crust and the cool, rigid uppermost mantle behave as one strong layer — the lithosphere — which averages at least 80 kilometres thick over much of the planet. This is the layer that is broken into plates.[1,2]
Beneath it lies the asthenosphere: a relatively narrow, mobile zone in the mantle whose material softens and flows under high temperature and pressure over geological time. The rigid plates are thought to move over it.[1,2]
The plates carry both continents and ocean floor, and the crust in each is different. Oceanic crust varies little in thickness and generally reaches only about five kilometres. Continental crust averages about thirty, and beneath large ranges its base can lie as deep as a hundred.[1,2,3]
That difference decides what happens when plates meet. Continental rocks are relatively light and resist being drawn downward; where two continents converge, neither goes down and the crust buckles instead.[1,2]
The plates are lithospheric, not continental. Each carries both continental and oceanic areas, which is why plate boundaries so often run through ocean floor rather than around coastlines.[1]
Often said
“The tectonic plates are the continents.”
What the evidence supports
Plates are pieces of lithosphere — crust together with the rigid uppermost mantle — and a single plate typically carries both continental and oceanic areas. Continents ride on plates; they are not the plates.
Supporting records: plates-are-lithosphere · lithosphere-nature
Often said
“Continents float on a layer of magma.”
What the evidence supports
What lies beneath the plates is the asthenosphere: solid mantle material that flows slowly over geological time. The plates move over solid rock that deforms, not over liquid.
Supporting records: lithosphere-float · mantle-solid-flow · asthenosphere-definition
Bracketed references link to the structured entity records whose claims support each paragraph. Last updated 2026-09-06.