Rocks are heated, metamorphosed, melted,
weathered, sediment is transported, deposited and lithified, then it may be metamorphosed
again in yet another cycle. This recycling of the material of the Earth's crust has
been going on for billions of years, as far back as there is a preserved geologic record
(about 4 billion years). Weathering and erosion at the Earth's surface can break
down rocks into small bits. These can be
deposited as sediments that become sedimentary
rocks. Burial, with rising pressure and temperature, can alter sedimentary (as well as any
other) rocks to form metamorphic rocks.
Continued rise in temperature can eventually melt
rocks and produce magma. Cooling of magmas leads to igneous rocks, etc.
