• core
    The core is the hottest part of the Earth.

    Illustration by Chuck Carter

    Planetary Cores
    All known planets have metal cores. Even the gas giants of our solar system, such as Jupiter and Saturn, have iron and nickel at their cores.

    Earth’s core is the very hot center of our planet.

    The Earth has three major layers. All known life exists on the solid outer layer, called the crust. Beneath the crust is the mantle, a gooey, hot layer of magma and other semi-solid rocks and minerals. Movement in the mantle leads to tectonic activity, such as volcanic eruptions and earthquakes, on the crust.

    The core, beneath the mantle, is the deepest and hottest layer of the Earth. It is made almost entirely of metal. The core is made of two layers: the outer core, which borders the mantle, and the inner core. The inner core is shaped like a ball.

    Scientists say the outer core is made mostly of iron and nickel. Iron and nickel are two important metals found everywhere on the planet. (On the surface of the Earth, these metals are found in solid form.) Iron and nickel in the outer core form an alloy, or a mixture of metallic elements. The outer core is approximately 2,300 kilometers (1,430 miles) thick. The alloy of the outer core is very hot, between 4,000 and 5,000 degrees Celsius (7,200 and 9,000 degrees Fahrenheit).

    The inner core is made mostly of iron. It is approximately 1,200 kilometers (750 miles) thick. Although the iron is extremely hot—between 5,000 and 7,000 degrees Celsius (9,000 and 13,000 degrees Fahrenheit)—the pressure from the rest of the planet is so great that the iron cannot melt. For this reason, the inner core is mostly solid.

    Because the Earth has a ball of metal in the middle of it, the entire planet is magnetic. Scientists believe the liquid outer core is what controls the Earth’s magnetic field. The magnetic field acts almost like a bubble. It protects the planet from charged particles floating around in the solar system, such as those from the sun. The magnetic North and South Poles are opposing sides of Earth’s big magnet.

    The hard, metallic material in the core is balled up in the center of the Earth because it's the heaviest material on the planet. When Earth was formed about 4.5 billion years ago, all the heavier substances sank toward the middle. The lighter and less dense material, such as air and water, stayed closer to the crust.

    Inside the core, the metals are constantly moving. The core of the Earth rotates regularly. Some scientists say the inner core actually rotates faster than the rest of the planet! As the liquid outer core moves, it can change the location of the magnetic North and South Poles.

  • Term Part of Speech Definition Encyclopedic Entry
    air Noun

    the layer of gases surrounding Earth.

    Encyclopedic Entry: air
    alloy Noun

    mixture of two or more metals.

    approximately Adjective

    generally or near an exact figure.

    border Verb

    to exist on the edge of a boundary.

    charged particle Noun

    molecule that has a positive or negative electric charge.

    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
    dense Adjective

    having parts or molecules that are packed closely together.

    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.

    element Noun

    chemical that cannot be separated into simpler substances.

    Europa Noun

    moon of Jupiter.

    gas giant Noun

    one of the four enormous outermost planets in the solar system (Jupiter, Saturn, Neptune, Uranus), composed mostly of gases instead of rock. Also called a Jovian planet.

    inner core Noun

    deepest layer of the Earth, beneath the outer core.

    Jupiter Noun

    largest planet in the solar system, the fifth planet from the Sun.

    magma Noun

    molten, or partially melted, rock beneath the Earth's surface.

    Encyclopedic Entry: magma
    magnetic Adjective

    able to produce a force field that can attract or repel certain substances, usually metals (magnets).

    magnetic field Noun

    area around and affected by a magnet or charged particle.

    magnetic north Adjective

    direction that all compass needles point.

    mantle Noun

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

    Encyclopedic Entry: mantle
    mineral Noun

    inorganic material that has a characteristic chemical composition and specific crystal structure.

    moon Noun

    natural satellite of a planet.

    Encyclopedic Entry: moon
    nickel Noun

    chemical element with the symbol Ni.

    outer core Noun

    layer of the Earth between the mantle and the inner core.

    planet Noun

    large, spherical celestial body that regularly rotates around a star.

    Encyclopedic Entry: planet
    rock Noun

    natural substance composed of solid mineral matter.

    rotate Verb

    to turn around a center point or axis.

    Saturn Noun

    sixth planet from the sun.

    solar system Noun

    the sun and the planets, asteroids, comets, and other bodies that orbit around it.

    substance Noun

    physical material.

    tectonic activity Noun

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

    volcanic eruption Noun

    activity that includes a discharge of gas, ash, or lava from a volcano.

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