The Earth's mantle is primarily composed of a semi-molten rock called magma, although a significant portion is solid due to immense pressure.
Composition and Structure of the Mantle
The mantle, situated between the Earth's crust and core, isn't a uniform entity. It's broadly divided into two main sections:
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Upper Mantle: This region is partially molten, containing the asthenosphere, a viscous layer that allows the tectonic plates to move. Magma in this region is the source of many volcanic eruptions.
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Lower Mantle: The lower mantle is predominantly solid rock, though still incredibly hot. The immense pressure prevents it from fully melting. The reference indicates that this rock is hot enough to melt but stays solid due to the pressure.
Key Components
While the reference mentions "a semi-molten rock called magma" which is a good high-level summary, it is useful to provide more detail. The mantle is largely composed of silicate rocks rich in iron and magnesium. These include:
- Olivine: A magnesium-iron silicate with the formula (Mg,Fe)₂SiO₄
- Pyroxene: A group of silicate minerals with varying compositions, generally (Mg,Fe,Ca)₂Si₂O₆
- Perovskite: A calcium-titanium oxide mineral, CaTiO₃, abundant in the lower mantle due to the immense pressure.
Key Characteristics
- Temperature: The temperature of the mantle varies significantly with depth, ranging from approximately 1000°C (1832°F) near the crust to 3700°C (6692°F) near the core.
- Pressure: Pressure increases dramatically with depth, influencing the physical state of the mantle material.
- Convection: Heat from the Earth's core causes convection currents within the mantle, driving plate tectonics.
In summary, the Earth's mantle is composed of both solid and semi-molten rock rich in silicates like olivine, pyroxene, and perovskite. The intense heat and pressure affect the state of the material at different depths.
