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3.18: Earth's Mantle

  • Page ID
    5356
  • What does mantle rock look like?

    You can't go to the mantle, but small pieces of the mantle can come to you. Kimberlite forms deep in the mantle and can emerge in the crust during violent eruptions. Kimberlite can contain diamonds. Most kimberlite reached the surface much earlier in Earth's history.

    Mantle

    Beneath the crust is the mantle. The mantle is made of hot, solid rock. Scientists know this because of seismic waves, meteorites, and the heat that comes from inside the planet. Mantle rock is mostly peridotite, which is rich in iron and magnesium (Figure below). Peridotite is rare at Earth's surface.

    Peridotite is formed of crystals of olivine and pyroxene

    The rock of the mantle is mostly peridotite. Peridotite is formed of crystals of olivine (green) and pyroxene (black).

    Conduction and Convection

    Through the process of conduction, thermal energy flows from warmer objects to cooler objects (Figure below). This transfer of energy is known as heat. The lower mantle is heated directly by conduction from the core. In conduction, energy is transferred as atoms collide.

    In the process of conduction, heat flows from warmer objects to cooler objects

    In the process of conduction, thermal energy flows from warmer objects to cooler objects.

    Hot lower mantle material rises upward (Figure above). As it rises, it cools. At the top of the mantle it moves horizontally. Over time it becomes cool and dense enough that it sinks. Back at the bottom of the mantle, it travels horizontally. Eventually the material gets to the location where warm mantle material is rising. The rising and sinking of warm and cooler material is called convection.

    Summary

    • The mantle is composed of solid peridotite.
    • Conduction from the core heats the lower mantle.
    • Mantle convection brings hot material up toward the surface. It brings cooler material down toward the core.

    Review

    1. How do scientists know what the mantle is made of?
    2. What is conduction?
    3. How does convection work in the mantle?

    Explore More

    Use this resource to answer the questions that follow.

    1. In which ocean did researchers try to drill into the mantle in 1961? In 2016?
    2. How much of Earth is made of mantle?
    3. Where in the ocean would you have the best chance of drilling to the mantle?
    4. Why did the researchers stop drilling in 1961?
    5. What noteworthy sample did researchers bring to the surface in 2016?
    6. What happens at the Moho discontinuity?
    7. What are extremophiles? Where do they live?
    8. How deep did the drilling go in 2016? How deep do they hope to get?
    9. What do scientists hope to find? Why would that sort of thing be found inside Earth?
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