Volcanoes.

• The Earth's structure consists of different layers: the inner core, the outer core, the mantle, and the crust.
• The inner core is the hottest part of the Earth, is solid, and is made up of iron and nickel with temperatures of up to 5,500°C.
• The outer core is a liquid layer surrounding the inner core, also made up of iron and nickel.
• The mantle is the thickest section of the Earth at approximately 2,900 kilometres, and the upper part of the mantle is called the asthenosphere, which is made up of semi-molten rock called magma.
• The crust is the surface of the Earth, forming the upper part of the lithosphere, and is a rock layer.
• The lithosphere is the outer layer of the Earth, which includes both the crust and the upper layers of the mantle, and is split into tectonic plates.
• The Earth's crust is the outer layer of the Earth, a thin layer between 0 - 60 km thick, and is the solid rock layer upon which we live.
• Ridge push is where the new crust formed at divergent plate margins is less dense than the surrounding crust and so it rises to form oceanic ridges.
• The movement of the plates and the activity inside the Earth, is called the theory of plate tectonics.
• Sinking in one place leads to plates moving apart in other places.
• It was once believed that convection currents in the mantle caused the plates to move, however, it is now recognised to be more complicated than this.
• Instead of tectonic plates moving because of the convection currents, evidence suggests it is the plates that drive the convection.
• The Earth's crust is broken into tectonic plates.
• Slab pull occurs where older, denser tectonic plates sink into the mantle at subduction zones.
• Mechanisms called slab pull and ridge push are believed to move the tectonic plates.
• The older seafloor either side of the ridge slides away and this moves the seafloor apart – moving the tectonic plates.
• As these older sections of plates sink, newer and less dense sections of plate are pulled along behind.