Illustration showing the Earth's internal structure.
The external layer shows the Earth's surface topography and atmosphere, including land, water and clouds. This rocky crust is 10-70 km thick. The mantle (red) is a viscous layer of rocks under high pressures and temperatures, extending downwards to a depth of around 2900 km. The outer core (yellow) is a liquid layer of iron and nickel, around 2200 km thick. The inner core (centre) is a liquid sphere of a iron-nickel alloy, with a radius of 1278 km.
Image: Illustrator Gary Hincks
Source: Photolibarary
Detail of grey granite, quarried at Harcourt, near Mt Alexander, Victoria, Australia.
The thickness of the Earth’s crust is about 70 km on continents. The continents are composed of light rocks, mostly granite and sediments, so they float higher on the mantle than the oceanic crust.
Image: Nicole Alley
Source: Museum Victoria
Detail of basalt platform at Point Gellibrand, Williamstown, Victoria.
The oceanic crust is mainly basalt, a dense volcanic rock.
The Earth’s crust is about 10 km thick below the oceans.
Image: Bill Birch
Source: Museum Victoria
Augite (black rock on left), cone of Mount Franklin, near Daylesford, Victoria, Australia and Anorthoclase (brown rock back right), The Anakies, Victoria, Australia.
We cannot reach the lower crust beneath the continents. But we know something about it from the rocks and minerals that volcanic eruptions sometimes bring to the surface. These rocks are mainly metamorphic, formed at high temperatures and pressures.
Source: Museum Victoria
Olivine, Western District, Victoria, Australia.
The Earth’s mantle is composed mainly of silicate minerals such as bright green olivine. We know this because molten rock from the mantle, called magma, is brought to the surface during volcanic eruptions.
Image: Kate Phillips
Source: Museum Victoria
Illustration of Earth's magnetic field.
The outer core of the Earth is molten iron with small amounts of nickel. As this liquid metal flows around the solid core it generates electrical currents, which create the Earth’s magnetic field. This protects the planet from harmful radiation from the Sun and space.
Image: Mark Garlick
Source: Photolibrary
Detail of Toluca meteorite, near Xiquipilco, Toluca, Mexico State, Mexico.
The Earth’s inner core is a mass of solid metal similar in composition to iron–nickel meteorites, and it is very hot – over 5000 °C. This intense heat generates slowly circulating convection currents in the overlying mantle, driving the movements of the Earth’s crustal plates and forming magma.
Image: Kate Phillips
Source: Museum Victoria
Planet Earth has layers made of different materials: an outer crust, a mantle and a core at its centre.
The crust is a very thin layer of rock – basalt below the oceans (10 km thick), and granite and sedimentary rocks on the continents (up to 70 km thick). Under the crust is the mantle, a semi-solid layer 2830 km thick. It is composed mainly of silicate minerals such as olivine. We get clues about its composition when molten rock from this layer comes to the surface during volcanic eruptions.
Below the mantle, the outer core is a layer of slow-moving liquid metal. It generates electrical currents as it flows and these create Earth’s magnetic field. Right in the centre of the Earth, the inner core is a solid mass of hot metal reaching over 5000 °C.