Earth and atmosphere, Year 8: more practice

Igneous rock forms from molten magma, which would destroy any remains

HintThink about how hot the liquid stone is underground.

The whySedimentary rock forms in layers at low temperature, so the remains can be buried and preserved.

Igneous

HintCrystals grow as a molten rock cools.

The whyGranite formed as magma cooled slowly underground, giving time for large crystals to grow.

Metamorphic

HintThe original rock was changed but did not melt.

The whyMetamorphic rocks form from existing rocks that are altered by heat and pressure without melting.

Sedimentary

HintLayers of fragments are the clue.

The whySandstone forms from sand laid down in layers and cemented together over a long time.

Deposition

HintThe fragments are being laid down.

The whyDeposition happens when moving water or wind slows down and drops the sediment it carried.

Compaction

HintThe layers are pressed closer together.

The whyCompaction squeezes the sediment together and cementation then sticks the grains together.

It is heated and squeezed (without melting)

HintThink about being buried deep in the Earth.

The whyHeat and pressure change the rock into a new metamorphic rock while it stays solid.

Magma

HintIt is the underground version of what erupts from a volcano as lava.

The whyWhen magma cools and hardens it forms igneous rock, completing the cycle.

Weathering, burial and uplift are all extremely slow processes

HintThink about how fast a mountain wears away.

The whyEach step of the cycle works slowly, so a full cycle takes a great many years.

Uplift

HintRocks do not stay buried forever.

The whyEarth movements push buried rocks upwards, bringing them to the surface where weathering can begin the cycle again.