• lithosphere
    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
    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.

    Encyclopedic Entry: volcano
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