How are rocks recycled?

The rock cycle

The forces of nature are constantly morphing rocks into different forms

1 Igneous rock

Igneous, which means ‘born of fire or heat’, is the rock type formed when molten magma cools enough to become solid. Intrusive igneous rock forms when the magma cools slowly under the Earth’s surface, and extrusive igneous rock forms when the magma cools rapidly on the surface, such as after a volcanic eruption.

 2 Rising heat

The intense heat found below the surface – sometimes stemming from the planet’s superheated core – can generate temperatures up to 1,300 degrees Celsius, causing the rock to melt into a molten form called magma, which rises towards the cooler surface via convection.

The Rock Cycle

 3 Metamorphic rock

The combination of intense pressure and high temperatures (between 300 and 700 degrees Celsius) doesn’t melt rocks but changes their chemical structure. They are transformed into dense metamorphic rock.

 4 Plate tectonics

Our planet’s crust is formed of tectonic plates, which are always moving very slowly. When these plates collide, mountains are formed and earthquakes are generated, and the friction also results in huge amounts of heat and pressure below the surface.

 5 Sedimentary rock

When sediments eventually settle, they are deposited in layers that accumulate over millions of years. The weight of the layers compresses the sediments at the bottom, squeezing out water and enabling crystals to form. These crystals act a bit like cement, gluing the pieces of rock together.

 6 Weathering and erosion

Weather conditions such as heat, wind, rain, snow, and ice take their toll on mountains and cliffs, and the rocks are slowly eroded, breaking them into smaller fragments called sediments. These are then carried away within bodies of water, such as streams and rivers.

How are rocks recycled?

How the rocks on our planet are weathered, worn and transformed countless times

Our planet is covered with different types of rock, from great mountains to molten magma to grains of sand – and all of these forms are connected by the rock cycle. This model shows how the three main classifications of rock – igneous, sedimentary and metamorphic – are able to morph into one another as different forces act upon them. Wind, rain, snow, and ice gradually erode mountains and cliffs to provide the material that will eventually be compacted to become sedimentary rock. 

The internal structure of our planet also plays an important role. The mantle – a 2,900-kilometre-thick, semi-molten region found beneath the Earth’s crust – provides extreme heat and pressure that compact rock into a metamorphic form. The planet’s core generates intense heat that melts the lower mantle into magma. This magma becomes igneous rock as it cools, either at the Earth’s crust or above the surface when it is ejected in volcanic eruptions.

The rock cycle is a story of rebirth and recycling, where the old provides materials for the new. The cycle takes thousands if not millions of years, but we can see snapshots of the process: waves crashing against rocks, shifting glaciers and dramatic volcanic eruptions all provide glimpses of the processes that govern Earth’s ever-changing geology.