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.

Vocabulary

Term Part of Speech Definition Encyclopedic Entry

coast

Noun

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

Encyclopedic Entry: coast

continent

Noun

one of the seven main land masses on Earth.

Encyclopedic Entry: continent

core

Noun

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

Encyclopedic Entry: core

crust

Noun

rocky outermost layer of Earth or other planet.

Encyclopedic Entry: crust

Earth

Noun

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

Encyclopedic Entry: Earth

earthquake

Noun

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

geologic

Adjective

having to do with the physical formations of the Earth.

iron

Noun

chemical element with the symbol Fe.

landmass

Noun

large area of land.

lithosphere

Noun

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

Encyclopedic Entry: lithosphere

mantle

Noun

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

Encyclopedic Entry: mantle

ocean

Noun

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

Encyclopedic Entry: ocean

Pangaea

Noun

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

plate tectonics

Noun

movement and interaction of the Earth's plates.

tectonic plate

Noun

large, moveable segment of the Earth's crust.

volcano

Noun

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

Credits

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Writer

Kim Rutledge
Melissa McDaniel
Diane Boudreau
Tara Ramroop
Santani Teng
Erin Sprout
Hilary Costa
Hilary Hall
Jeff Hunt

Illustrator

Tim Gunther
Mary Crooks, National Geographic Society

Editor

Kara West
Jeannie Evers

Educator Reviewer

Nancy Wynne

Producer

Caryl-Sue, National Geographic Society

Sources

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

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