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structure of the Earth click to hear : structure of the Earth

The Earth is formed of three concentric layers: the core, the mantle and the crust; these are separated by transition zones called discontinuities.
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lithosphere continental crust asthenosphere Mohorovicic discontinuity Gutenberg discontinuity lower mantle outer core inner core oceanic crust Earth’s crust upper mantle

lithosphere click to hear : lithosphere

Layer from 50 to 100 km thick that comprises the Earth’s crust and the solid part of the upper mantle; it is divided into tectonic plates.

continental crust click to hear : continental crust

Layer varying in thickness from 30 to 70 km and composed mainly of granite. It forms a number of distinct landforms: the continents.

asthenosphere click to hear : asthenosphere

Layer of the upper mantle with a thickness of 200 km; it is composed of molten rock, on top of which the lithospheric plates slide.

Mohorovicic discontinuity click to hear : Mohorovicic discontinuity

Zone that separates the Earth’s crust from the asthenosphere.

Gutenberg discontinuity click to hear : Gutenberg discontinuity

Zone separating the lower mantle from the core; it is located at a depth of about 2,900 km.

lower mantle click to hear : lower mantle

Little-known layer with a thickness of about 2,290 km; its slow-moving currents, called convention currents, are caused by temperature variations.

outer core click to hear : outer core

Composed of molten metal, it is 1,820 km thick; the magnetic field is caused by electric currents circulating inside the outer core.

inner core click to hear : inner core

Composed of iron and nickel, it is subject to so much pressure that it remains in a solid state in spite of temperatures higher than 5,000°C; its diameter is 1,600 km.

oceanic crust click to hear : oceanic crust

Layer forming the ocean floor; it is thinner, denser and younger than the continental crust.

Earth’s crust click to hear : Earth’s crust

Solid layer at the Earth’s surface whose thickness varies from 10 km beneath the oceans to 60 km beneath the mountains.

upper mantle click to hear : upper mantle

Layer of hard rock nearly 630 km thick; it is made up of the asthenosphere and the base of the lithosphere.