The Rock Cycle
Understand the rock cycle: rocks slowly change from one type to another over millions of years — igneous rock weathers into sediment, sediment becomes sedimentary rock, heat and pressure create metamorphic rock, and melting starts the cycle again
What a learner can do afterwards
- Describe the rock cycle as a continuous process with no beginning or end
- Trace at least one complete path through the cycle from igneous to sedimentary to metamorphic and back
- Explain that the rock cycle operates over millions of years through weathering, pressure, heat, and melting
The lesson
Rocks are always changing, just very slowly. Over millions of years, one type of rock can turn into another, and then into another. This never stops, and it has no true beginning and no true end, so scientists call it the rock cycle.
Picture a granite mountain, an igneous rock. Wind and rain slowly break it into tiny grains of sand. The sand piles up in a riverbed and presses together into sandstone, a sedimentary rock. Later, that sandstone gets buried deep underground, where heat and pressure squeeze it into quartzite, a metamorphic rock. If the quartzite ever melts, it becomes magma again, ready to cool into new igneous rock.
This whole trip, from igneous rock to sediment to sedimentary rock to metamorphic rock and back to melted rock, usually takes millions of years. You will never see it happen, but it is happening under your feet right now.
Rock never stops changing: it weathers, presses, heats, and melts its way around the rock cycle, forever.
Watch it
Where it sits
This opens up
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.