Earth and atmosphere, Year 8: more practice

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

提示Think about how hot the liquid stone is underground.

为什么Sedimentary rock forms in layers at low temperature, so the remains can be buried and preserved.

Igneous

提示Crystals grow as a molten rock cools.

为什么Granite formed as magma cooled slowly underground, giving time for large crystals to grow.

Metamorphic

提示The original rock was changed but did not melt.

为什么Metamorphic rocks form from existing rocks that are altered by heat and pressure without melting.

Sedimentary

提示Layers of fragments are the clue.

为什么Sandstone forms from sand laid down in layers and cemented together over a long time.

Deposition

提示The fragments are being laid down.

为什么Deposition happens when moving water or wind slows down and drops the sediment it carried.

Compaction

提示The layers are pressed closer together.

为什么Compaction squeezes the sediment together and cementation then sticks the grains together.

It is heated and squeezed (without melting)

提示Think about being buried deep in the Earth.

为什么Heat and pressure change the rock into a new metamorphic rock while it stays solid.

Magma

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

为什么When magma cools and hardens it forms igneous rock, completing the cycle.

Weathering, burial and uplift are all extremely slow processes

提示Think about how fast a mountain wears away.

为什么Each step of the cycle works slowly, so a full cycle takes a great many years.

Uplift

提示Rocks do not stay buried forever.

为什么Earth movements push buried rocks upwards, bringing them to the surface where weathering can begin the cycle again.