Plate tectonics explains how Earth’s rigid outer shell is divided into moving pieces and how their motion reshapes the planet. This lesson introduces the layers and materials involved, and shows why plate motion matters.
Earth’s outer layers are described in two different ways. In a mechanical classification, the lithosphere is the cool, rigid outer shell, made up of the crust and the uppermost mantle. Beneath it is the asthenosphere, a hotter region of the upper mantle that is solid but can flow slowly over long periods.
All flashcards
What is the lithosphere?
Earth’s cool, rigid outer shell, consisting of the crust and the rigid uppermost mantle.
What is the asthenosphere?
A hotter, ductile region of the mantle beneath the lithosphere that can deform and flow slowly over geological time.
What is a tectonic plate?
A relatively rigid piece of lithosphere that moves over the more deformable asthenosphere.
Can a plate contain both kinds of crust?
Yes. A plate can include oceanic crust, continental crust, or both, along with the lithospheric mantle beneath them.
What geological activity commonly occurs at plate boundaries?
Earthquakes, volcanic activity, mountain building, and the formation of oceanic trenches can occur where plates interact.
Quiz questions
At a subduction zone, how can water released from a sinking plate help produce volcanoes?Answer: It lowers the melting point of mantle material above the slab.
What commonly happens when two continental masses converge?Answer: Their crust is compressed and uplifted, building mountain ranges.
What generally happens to crust at a transform boundary?Answer: It is neither created nor destroyed as plates slide past.
What do symmetrical magnetic stripes on either side of a mid-ocean ridge support?Answer: New seafloor forms at the ridge and spreads outward.
What is an ophiolite?Answer: A fragment of oceanic crust preserved within continental crust.
Based on the Wikipedia article Plate tectonics, licensed CC BY-SA 4.0. Adapted into a summary, flashcards and quizzes.