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The Earth and the rock cycle
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The Earth is made of layers, and its rocks are slowly recycled over millions of years.
Structure and composition
Mantle: very hot rock that is mostly solid but can flow very slowly.
Outer core: liquid iron and nickel.
Inner core: solid iron and nickel, the hottest part.
Three types of rock
The rock cycle
Weathering breaks rock into pieces. Erosion and transport carry them away. Deposition lays them down as sediment, which is compacted and cemented into sedimentary rock.
Buried rock can be heated and squeezed into metamorphic rock, or melt into magma, which cools to form igneous rock. Uplift brings rocks back to the surface.
Granite has large crystals and basalt has small crystals. Explain why.
- Both are igneous rocks formed from molten rock.
- Granite cooled slowly underground, so crystals had time to grow.
- Basalt cooled quickly at the surface, so crystals stayed small.
Answer: Granite cooled slowly underground (big crystals); basalt cooled quickly at the surface (small crystals).
Crust, mantle, liquid outer core, solid inner core (iron and nickel). Igneous rock forms from cooled magma or lava; sedimentary from compacted, cemented layers; metamorphic from heat and pressure. Weathering, erosion, deposition and melting drive the rock cycle.
The interactive lesson includes the diagrams for this topic.
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