• Earth's interior is generally divided into three major layers: the crust, the mantle, and the core.


    The hard, brittle crust extends from Earth's surface to the so-called Mohorovicic discontinuity, nicknamed the Moho. The Moho is not located at a uniform depth, but about 10 kilometers (6 miles) below the seafloor and about 35 kilometers (22 miles) beneath the surface of continents.


    Beneath the Moho is the mantle, the viscous layer that makes up more than half of Earth's volume.


    The mantle is divided from the core by the Gutenberg discontinuity, about 2,880 kilometers (1,798 miles) beneath Earth's surface. The outer core is molten and liquid iron and nickel, while the inner core is solid and much more dense than either iron or nickel at the surface.

    1. Which lies deeper beneath the Earth's crust—the Gutenberg discontinuity or the Moho?

      The Gutenberg discontinuity, the boundary between the mantle and core, lies much deeper than the Moho, which separates Earth's crust and mantle.

    2. What region of Earth's interior do you think is the most rigid and brittle?

      The rocky outer crust—where we live and breathe!—is the most brittle layer of Earth.

    3. Which region of Earth do you think is the hottest?

      The super-dense inner core is the hottest of Earth's layers. This region is about as hot as the Sun!

  • Term Part of Speech Definition Encyclopedic Entry
    brittle Adjective

    fragile or easily broken.

    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
    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
    Gutenberg discontinuity Noun

    point between the Earth's mantle and the core below.

    mantle Noun

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

    Encyclopedic Entry: mantle
    Mohorovicic discontinuity Noun

    point between Earth's crust and the mantle below. Also called the Moho.

    seafloor Noun

    surface layer of the bottom of the ocean.

    viscous Adjective

    liquid that is thick and sticky.

    volume Noun

    space an object occupies.