Encyclopedic Entry

All terrestrial planets have lithospheres. The lithospheres of Mercury, Venus, and Mars are much thicker and more rigid than Earth's.

Photograph by Jennifer Plourde, MyShot

Former Neighbors
Fossils of the same reptiles have been found in both South America and Africa. The fossils were even found in the same layers, in the same type of earth, a full ocean away. Scientists say this is evidence that the continents were once one giant landmass called Pangaea.

The lithosphere is the solid, outer part of the Earth. The Earth consists of three main layers: the core, or the inner layer; the mantle, in the middle; and the crust, which includes the continents and ocean floor. The lithosphere, which is about 100 kilometers (60 miles) deep in most places, includes the brittle upper portion of the mantle and the crust.

The lithosphere is always moving, but very slowly. It is broken into huge sections called tectonic plates. The extreme heat from the mantle part of the lithosphere makes it easier for the plates to move; this is similar to how iron is bendable once it's heated. The movement of the lithosphere, called plate tectonics, is the reason behind a lot of Earth's most dramatic geologic events. When one plate moves beneath another, or when two plates rub together, they can create earthquakes and volcanoes.

The U.S. state of Hawaii was formed on a tectonic plate called the Pacific plate. Its islands are in a chain because the plate was constantly moving above the mantle.

Plate tectonics may explain why we have continents. Scientists believe the continents used to be one major landmass called Pangaea, which separated because the lithosphere broke apart. There is evidence to support this theory. For example, the eastern coast of South America and the western coast of Africa look like they would fit together. And even though they are separated by an ocean, similar animals and plants are found in both regions.


Term Part of Speech Definition Encyclopedic Entry



edge of land along the sea or other large body of water.

Encyclopedic Entry: coast



one of the seven main land masses on Earth.

Encyclopedic Entry: continent



the extremely hot center of Earth, another planet, or a star.

Encyclopedic Entry: core



rocky outermost layer of Earth or other planet.

Encyclopedic Entry: crust



our planet, the third from the Sun. The Earth is the only place in the known universe that supports life.

Encyclopedic Entry: Earth



the sudden shaking of Earth's crust caused by the release of energy along fault lines or from volcanic activity.



having to do with the physical formations of the Earth.



chemical element with the symbol Fe.



large area of land.



outer, solid portion of the Earth. Also called the geosphere.

Encyclopedic Entry: lithosphere



middle layer of the Earth, made of mostly solid rock.

Encyclopedic Entry: mantle



large body of salt water that covers most of the Earth.

Encyclopedic Entry: ocean



supercontinent of all the Earth's landmass that existed about 250 million years ago.

plate tectonics


movement and interaction of the Earth's plates.

tectonic plate


large, moveable segment of the Earth's crust.



an opening in the Earth's crust, through which lava, ash, and gases erupt, and also the cone built by eruptions.


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Kim Rutledge
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Diane Boudreau
Tara Ramroop
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Erin Sprout
Hilary Costa
Hilary Hall
Jeff Hunt


Tim Gunther
Mary Crooks, National Geographic Society


Kara West
Jeannie Evers

Educator Reviewer

Nancy Wynne


Caryl-Sue, National Geographic Society


Dunn, Margery G. (Editor). (1989, 1993). "Exploring Your World: The Adventure of Geography." Washington, D.C.: National Geographic Society.

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