What makes up the mantle of the earth

The other major type of rock found in the mantle is magnesium oxide. Other mantle elements include iron, aluminum, calcium, sodium, and potassium. In the mantle, heat and pressure generally increase with depth. The geothermal gradient is a measurement of this increase. The viscosity of the mantle also varies greatly. It is mostly solid rock, but less viscous at tectonic plate boundaries and mantle plumes. Mantle rocks there are soft and able to move plastically over the course of millions of years at great depth and pressure.

The transfer of heat and material in the mantle helps determine the landscape of Earth. Activity in the mantle drives plate tectonics , contributing to volcano es, seafloor spreading , earthquake s, and orogeny mountain-building. The upper mantle extends from the crust to a depth of about kilometers miles. The upper mantle is mostly solid, but its more malleable regions contribute to tectonic activity.

The lithosphere is the solid, outer part of the Earth, extending to a depth of about kilometers 62 miles. The lithosphere includes both the crust and the brittle upper portion of the mantle. Tectonic activity describes the interaction of the huge slab s of lithosphere called tectonic plate s. The division in the lithosphere between the crust and the mantle is called the Mohorovicic discontinuity , or simply the Moho.

The Moho does not exist at a uniform depth, because not all regions of Earth are equally balanced in isostatic equilibrium. The Moho is found at about 8 kilometers 5 miles beneath the ocean and about 32 kilometers 20 miles beneath continents. Different types of rocks distinguish lithospheric crust and mantle. Lithospheric crust is characterize d by gneiss continental crust and gabbro oceanic crust.

Below the Moho, the mantle is characterized by peridotite, a rock mostly made up of the minerals olivine and pyroxene. The asthenosphere is the denser, weaker layer beneath the lithospheric mantle. The temperature and pressure of the asthenosphere are so high that rocks soften and partly melt, becoming semi-molten. The asthenosphere is much more ductile than either the lithosphere or lower mantle. The asthenosphere is generally more viscous than the lithosphere, and the lithosphere-asthenosphere boundary LAB is the point where geologist s and rheologist s—scientists who study the flow of matter—mark the difference in ductility between the two layers of the upper mantle.

In fact, the lava that erupts from volcanic fissure s is actually the asthenosphere itself, melted into magma. Of course, tectonic plates are not really floating, because the asthenosphere is not liquid.

Tectonic plates are only unstable at their boundaries and hot spots. In the transition zone, rocks do not melt or disintegrate. Instead, their crystal line structure changes in important ways. Rocks become much, much more dense. The transition zone prevents large exchanges of material between the upper and lower mantle.

Some geologists think that the increased density of rocks in the transition zone prevents subducted slabs from the lithosphere from falling further into the mantle. These huge pieces of tectonic plates stall in the transition zone for millions of years before mixing with other mantle rock and eventually returning to the upper mantle as part of the asthenosphere, erupting as lava, becoming part of the lithosphere, or emerging as new oceanic crust at sites of seafloor spreading.

Some geologists and rheologists, however, think subducted slabs can slip beneath the transition zone to the lower mantle. Other evidence suggests that the transition layer is permeable , and the upper and lower mantle exchange some amount of material. It is not liquid, vapor , solid, or even plasma. Instead, water exists as hydroxide. Hydroxide is an ion of hydrogen and oxygen with a negative charge.

In the transition zone, hydroxide ions are trapped in the crystalline structure of rocks such as ringwoodite and wadsleyite. These minerals are formed from olivine at very high temperatures and pressure. Near the bottom of the transition zone, increasing temperature and pressure transform ringwoodite and wadsleyite. This allows the transition zone to maintain a consistent reservoir of water. Subduction is the process in which a dense tectonic plate slips or melts beneath a more buoyant one.

Most subduction happens as an oceanic plate slips beneath a less-dense plate. Along with the rocks and minerals of the lithosphere, tons of water and carbon are also transported to the mantle. Hydroxide and water are returned to the upper mantle, crust, and even atmosphere through mantle convection, volcanic eruptions, and seafloor spreading.

The lower mantle is hotter and denser than the upper mantle and transition zone. The lower mantle is much less ductile than the upper mantle and transition zone. Although heat usually correspond s to softening rocks, intense pressure keeps the lower mantle solid. Geologists do not agree about the structure of the lower mantle.

Some geologists think that subducted slabs of lithosphere have settled there. Other geologists think that the lower mantle is entirely unmoving and does not even transfer heat by convection. In still other areas, geologists and seismologist s have detected areas of huge melt. The iron of the outer core influences the formation of a diapir , a dome -shaped geologic feature igneous intrusion where more fluid material is forced into brittle overlying rock.

The iron diapir emits heat and may release a huge, bulging pulse of either material or energy—just like a Lava Lamp. This energy blooms upward, transferring heat to the lower mantle and transition zone, and maybe even erupting as a mantle plume. At the base of the mantle, about 2, kilometers 1, miles below the surface, is the core-mantle boundary, or CMB. Mantle convection describes the movement of the mantle as it transfers heat from the white-hot core to the brittle lithosphere.

The mantle is heated from below, cooled from above, and its overall temperature decreases over long periods of time. All these elements contribute to mantle convection. Convection currents transfer hot, buoyant magma to the lithosphere at plate boundaries and hot spots. Earth's heat budget , which measures the flow of thermal energy from the core to the atmosphere, is dominate d by mantle convection. In this model, the mantle convects in a single process.

It eventually becomes cool and dense enough to sink back down into the mantle. At the bottom of the mantle, the material travels horizontally and is heated by the core. It reaches the location where warm mantle material rises, and the mantle convection cell is complete.

Scientists know that the core is metal for a few reasons. If the surface layers are less dense than average, then the interior must be denser than average. Calculations indicate that the core is about 85 percent iron metal with nickel metal making up much of the remaining 15 percent. Also, metallic meteorites are thought to be representative of the core. Metals such as iron are magnetic, but rock, which makes up the mantle and crust, is not. Scientists know that the outer core is liquid and the inner core is solid because S-waves stop at the inner core.

The strong magnetic field is caused by convection in the liquid outer core. Convection currents in the outer core are due to heat from the even hotter inner core.

The heat that keeps the outer core from solidifying is produced by the breakdown of radioactive elements in the inner core. Skip to main content. Plate Tectonics. Search for:. The Composition and Structure of Earth Core, mantle, and crust are divisions based on composition. Licenses and Attributions. In terms of its constituent elements, the mantle is made up of These elements are all bound together in the form of silicate rocks, all of which take the form of oxides.

Examples of rocks that you might find inside the mantle include: olivine, pyroxenes, spinel, and garnet. Whereas hot material rises to the surface, cooler, heavier material sinks beneath. The lithosphere is divided into a number of plates that are continuously being created and consumed at their opposite plate boundaries. Downward motion of material occurs in subduction zones, locations at convergent plate boundaries where one mantle layer moves under another.

Accretion occurs as material is added to the growing edges of a plate, associated with seafloor spreading. This chaotic process is believed to be an integral part of the motion of plates, which in turn gives rise to continental drift.

Subducted oceanic crust is also what gives rise to volcanism, as demonstrated by the Pacific Ring of Fire. Scientific investigations and exploration of the mantle is generally conducted on the seabed due to the relative thickness of the oceanic crust compared to the continental crust. The first attempt at mantle exploration known as Project Mohole achieved a deepest penetration of approximately meters feet.

It was abandoned in after repeated failures and cost over-runs. This would melt its way through the crust and mantle and communicate via acoustic signals generated by its penetration of the rocks.