• lithosphere
    The rocky lithosphere includes part of the upper mantle and crust.
    Extraterrestrial Lithospheres
    All terrestrial planets have lithospheres. The lithospheres of Mercury, Venus, and Mars are much thicker and more rigid than Earth's.
    Lithospheres
    Scientists have identified many ways to define the lithosphere. The “elastic lithosphere” measures its ability to reform itself under stress. The “thermal lithosphere” measures its temperature and the thermal energy—heat—it conducts. The “seismic lithosphere” measures how lithospheric rocks move with seismic shifts and tectonic activity. The “electrical lithosphere” measures the layer’s ability to conduct electricity (much lower than the asthenosphere). Finally, the “petrologic lithosphere” measures the chemical properties of rocks in the lithosphere compared to the asthenosphere.
    The LAB
    The depth of the lithosphere-asthenosphere boundary (LAB) is a hot topic among geologists and rheologists. These scientists study the upper mantle’s viscosity, temperature, and grain size of its rocks and minerals. What they have found varies widely, from a thin, crust-deep boundary at mid-ocean ridges to thick, 200-meter (124-mile) boundary beneath cratons, the oldest and most stable parts of continental lithosphere.
    The lithosphere is the solid, outer part of the Earth. The lithosphere includes the brittle upper portion of the mantle and the crust, the outermost layers of Earth’s structure. It is bounded by the atmosphere above and the asthenosphere (another part of the upper mantle) below.
     
    The lithosphere is the most rigid of Earth’s layers. Although the rocks of the lithosphere are still considered elastic, they are not viscous. The asthenosphere is viscous, and the lithosphere-asthenosphere boundary (LAB) is the point where geologists and rheologists—scientists who study the flow of matter—mark the difference in ductility between the two layers of the upper mantle. Ductility measures a solid material’s ability to deform or stretch under stress. The lithosphere is far less ductile than the asthenosphere. The elasticity and ductility of the lithosphere depends on temperature, stress, and the curvature of the Earth itself.
     
    The lithosphere is also the coolest of Earth’s layers. In fact, some definitions of the lithosphere stress its ability to conduct heat associated with the convection taking place in the plastic mantle below the lithosphere.
     
    There are two types of lithosphere: oceanic lithosphere and continental lithosphere. Oceanic lithosphere is associated with oceanic crust, and is slightly denser than continental lithosphere. Continental lithosphere, associated with continental crust, can be much, much thicker than its oceanic cousin, stretching more than 200 kilometers (124 miles) below Earth’s surface. 
     
    Plate Tectonics
     
    The most well-known feature associated with Earth’s lithosphere is tectonic activity. Tectonic activity describes the interaction of the huge slabs of lithosphere called tectonic plates.
     
    The lithosphere is divided into 15 major tectonic plates: the North American, Caribbean, South American, Scotia, Antarctic, Eurasian, Arabian, African, Indian, Philippine, Australian, Pacific, Juan de Fuca, Cocos, and Nazca.
     
    Most tectonic activity takes place at the boundaries of these plates, where they may collide, tear apart, or slide against each other. The movement of tectonic plates is made possible by thermal energy (heat) from the mantle part of the lithosphere. Thermal energy makes the rocks of the lithosphere more elastic.
     
    Tectonic activity is responsible for some of Earth's most dramatic geologic events: earthquakes, volcanoes, orogeny (mountain-building), and deep ocean trenches can all be formed by tectonic activity in the lithosphere. 
     
    Tectonic activity can shape the lithosphere itself: Both oceanic and continental lithospheres are thinnest at rift valleys and mid-ocean ridges, where tectonic plates are shifting apart from one another. At these zones, the lithosphere is only as thick as the crust.
     
    How the Lithosphere Interacts with Other Spheres
     
    The cool, brittle lithosphere is just one of five great “spheres” that shape the environment of Earth. The other spheres are the biosphere (Earth’s living things); the cryosphere (Earth’s frozen regions, including both ice and frozen soil); the hydrosphere (Earth’s liquid water); and the atmosphere (the air surrounding our planet). These spheres interact to influence such diverse elements as ocean salinity, biodiversity, and landscape.
     
    For instance, the pedosphere is part of the lithosphere made of soil and dirt. The pedosphere is created by the interaction of the lithosphere, atmosphere, cryosphere, hydrosphere, and biosphere. Enormous, hard rocks of the lithosphere may be ground down to powder by the powerful movement of a glacier (cyrosphere). Weathering and erosion caused by wind (atmosphere) or rain (hydrosphere) may also wear down rocks in the lithosphere. The organic components of the biosphere, including plant and animal remains, mix with these eroded rocks to create fertile soil—the pedosphere.
     
    The lithosphere also interacts with the atmosphere, hydrosphere, and cryosphere to influence temperature differences on Earth. Tall mountains, for example, often have dramatically lower temperatures than valleys or hills. The mountain range of the lithosphere is interacting with the lower air pressure of the atmosphere and the snowy precipitation of the hydrosphere to create a cool or even icy climate zone. A region’s climate zone, in turn, influences adaptations necessary for organisms of the region’s biosphere.
  • Term Part of Speech Definition Encyclopedic Entry
    adaptation Noun

    a modification of an organism or its parts that makes it more fit for existence. An adaptation is passed from generation to generation.

    Encyclopedic Entry: adaptation
    air pressure Noun

    force pressed on an object by air or atmosphere.

    asthenosphere Noun

    layer in Earth's mantle between the lithosphere (above) and the upper mantle (below).

    atmosphere Noun

    layers of gases surrounding a planet or other celestial body.

    Encyclopedic Entry: atmosphere
    biodiversity Noun

    all the different kinds of living organisms within a given area.

    Encyclopedic Entry: biodiversity
    biosphere Noun

    part of the Earth where life exists.

    Encyclopedic Entry: biosphere
    brittle Adjective

    fragile or easily broken.

    climate zone Noun

    area separated from others by its long-term weather patterns.

    component Noun

    part.

    continental crust Noun

    thick layer of Earth that sits beneath continents.

    convection Noun

    transfer of heat by the movement of the heated parts of a liquid or gas.

    crust Noun

    rocky outermost layer of Earth or other planet.

    Encyclopedic Entry: crust
    cryosphere Noun

    icy part of the Earth's waterincluding icebergs, glaciers, and ice caps.

    dense Adjective

    having parts or molecules that are packed closely together.

    diverse Adjective

    varied or having many different types.

    ductility Noun

    ability of a solid material to withstand stress or force by changing form instead of breaking.

    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.

    elastic Adjective

    able to bend easily.

    environment Noun

    conditions that surround and influence an organism or community.

    erosion Noun

    act in which earth is worn away, often by water, wind, or ice.

    Encyclopedic Entry: erosion
    fertile Adjective

    able to produce crops or sustain agriculture.

    geologic Adjective

    having to do with the physical formations of the Earth.

    geologist Noun

    person who studies the physical formations of the Earth.

    glacier Noun

    mass of ice that moves slowly over land.

    Encyclopedic Entry: glacier
    hill Noun

    land that rises above its surroundings and has a rounded summit, usually less than 300 meters (1,000 feet).

    Encyclopedic Entry: hill
    hydrosphere Noun

    all the Earth's water in the ground, on the surface, and in the air.

    Encyclopedic Entry: hydrosphere
    landscape Noun

    the geographic features of a region.

    Encyclopedic Entry: landscape
    lithosphere Noun

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

    Encyclopedic Entry: lithosphere
    lithosphere-asthenosphere boundary (LAB) Noun

    chemical and mechanical distinction between the cool, rigid lithosphere and the warmer, more ductile asthenosphere.

    mantle Noun

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

    Encyclopedic Entry: mantle
    mid-ocean ridge Noun

    underwater mountain range.

    mountain Noun

    landmass that forms as tectonic plates interact with each other.

    oceanic crust Noun

    thin layer of the Earth that sits beneath ocean basins.

    ocean trench Noun

    a long, deep depression in the ocean floor.

    Encyclopedic Entry: ocean trench
    organic Adjective

    composed of living or once-living material.

    orogeny Noun

    the way mountains are formed.

    pedosphere Noun

    layer of Earth consisting of soil and all it contains (such as water, air, organisms).

    plastic Noun

    chemical material that can be easily shaped when heated to a high temperature.

    precipitation Noun

    all forms in which water falls to Earth from the atmosphere.

    Encyclopedic Entry: precipitation
    precipitation Noun

    all forms in which water falls to Earth from the atmosphere.

    Encyclopedic Entry: precipitation
    rain Noun

    liquid precipitation.

    Encyclopedic Entry: rain
    remains Noun

    materials left from a dead or absent organism.

    rheologist Noun

    scientist who studies the flow and shape-changing (deformation) of matter.

    rift valley Noun

    depression in the ground caused by the Earth's crust spreading apart.

    Encyclopedic Entry: rift valley
    rigid Adjective

    stiff.

    rock Noun

    natural substance composed of solid mineral matter.

    salinity Noun

    saltiness.

    snow Noun

    precipitation made of ice crystals.

    soil Noun

    top layer of the Earth's surface where plants can grow.

    stress Verb

    to strain or put pressure on.

    tectonic activity Noun

    movement of tectonic plates resulting in geologic activity such as volcanic eruptions and earthquakes.

    tectonic plate Noun

    large, moveable segment of the Earth's crust.

    temperature Noun

    degree of hotness or coldness measured by a thermometer with a numerical scale.

    Encyclopedic Entry: temperature
    thermal energy Noun

    heat, measured in joules or calories.

    valley Noun

    depression in the Earth between hills.

    viscous Adjective

    liquid that is thick and sticky.

    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
    weathering Noun

    the breaking down or dissolving of the Earth's surface rocks and minerals.

    Encyclopedic Entry: weathering
    wind Noun

    movement of air (from a high pressure zone to a low pressure zone) caused by the uneven heating of the Earth by the sun.