#separator:tab #html:false #tags column:4 Crust Earth's thin, rocky outer layer earth-layers-landforms Mantle The thick layer of hot rock beneath the crust earth-layers-landforms Outer core A layer of liquid iron and nickel earth-layers-landforms Inner core A solid ball of iron and nickel at Earth's center earth-layers-landforms Which Earth layer is thickest? The mantle earth-layers-landforms Which Earth layer is thinnest? The crust earth-layers-landforms Continental crust The thicker crust that makes up the continents earth-layers-landforms Oceanic crust The thinner, denser crust under the oceans earth-layers-landforms Moho The boundary between the crust and mantle earth-layers-landforms Troposphere The lowest layer of the atmosphere, where weather happens earth-layers-landforms Stratosphere The atmosphere layer above the troposphere, holding the ozone layer earth-layers-landforms Mesosphere The layer where most meteors burn up earth-layers-landforms Thermosphere The layer where auroras happen and the space station orbits earth-layers-landforms Exosphere The outermost atmosphere layer fading into space earth-layers-landforms Ozone layer A layer that absorbs harmful ultraviolet light earth-layers-landforms Hydrosphere All the water on Earth earth-layers-landforms Lithosphere Earth's rigid outer shell earth-layers-landforms Biosphere All living things on Earth earth-layers-landforms Atmosphere The blanket of gases around Earth earth-layers-landforms Percent of Earth covered by water, about 71 percent earth-layers-landforms Percent of Earth's water that is salty, about 97 percent earth-layers-landforms Mountain A very high landform with steep sides earth-layers-landforms Hill A raised landform lower than a mountain earth-layers-landforms Valley Low land between hills or mountains earth-layers-landforms Canyon A deep valley with steep sides, often cut by a river earth-layers-landforms Plateau A high, flat landform earth-layers-landforms Plain A large flat area of land earth-layers-landforms Mesa A flat-topped hill with steep sides earth-layers-landforms Butte A small, steep-sided hill with a flat top earth-layers-landforms Peninsula Land surrounded by water on three sides earth-layers-landforms Island Land completely surrounded by water earth-layers-landforms Isthmus A narrow strip of land connecting two larger landmasses earth-layers-landforms Archipelago A group of islands earth-layers-landforms Delta Land built up where a river empties into a larger body of water earth-layers-landforms Cape A point of land that sticks out into water earth-layers-landforms Bay Part of the sea that curves into the land earth-layers-landforms Gulf A large bay earth-layers-landforms Strait A narrow waterway between two larger bodies of water earth-layers-landforms Lake A body of water surrounded by land earth-layers-landforms River A large stream flowing to a lake or sea earth-layers-landforms Tributary A stream that flows into a larger river earth-layers-landforms Source of a river Where a river begins earth-layers-landforms Mouth of a river Where a river ends earth-layers-landforms Watershed The area of land that drains into a river earth-layers-landforms Dune A hill of sand made by wind earth-layers-landforms Cave A natural hollow in rock or ground earth-layers-landforms Cliff A steep rock face earth-layers-landforms Glacier A large, slow-moving river of ice earth-layers-landforms Iceberg A large floating piece of ice broken from a glacier earth-layers-landforms Oasis A fertile spot in the desert with water earth-layers-landforms Reef A ridge of coral or rock near the surface of the sea earth-layers-landforms Atoll A ring-shaped coral island earth-layers-landforms Fjord A long, narrow sea inlet between steep cliffs earth-layers-landforms Tundra A cold treeless plain earth-layers-landforms Prairie A large grassy plain earth-layers-landforms Basin A low area where water collects earth-layers-landforms Elevation Height above sea level earth-layers-landforms Topographic map A map showing the shape and height of land with contour lines earth-layers-landforms Contour line A line on a map connecting points of equal elevation earth-layers-landforms Longitude Distance east or west of the Prime Meridian earth-layers-landforms Latitude Distance north or south of the Equator earth-layers-landforms Equator The imaginary line at 0 degrees latitude around Earth's middle earth-layers-landforms Axis The imaginary line Earth spins around earth-layers-landforms Rotation Earth spinning, one turn each day earth-layers-landforms Revolution Earth traveling around the Sun, one trip each year earth-layers-landforms Earth's axial tilt About 23.5 degrees earth-layers-landforms Cause of the seasons Earth's tilted axis as it orbits the Sun earth-layers-landforms Solstice The day with the most or least daylight in a year earth-layers-landforms Equinox A day when day and night are nearly equal earth-layers-landforms