After a body of water deposits layers of sediments, the grains in those layers, or strata, undergo various changes in response to the pressure of the layers on top of them. Scientists use the word diagenesis from the Greek roots dia (change) and genesis (origin) to encompass all these changes. In the process called cementation, minerals grow or precipitate out of solution in the pore spaces between rock or mineral grains. Compaction is the collapse of pore spaces within a sedimentary rock due to the weight of the rock above it. Lithification is the process of hardening sediment into rock through compaction and cementation. Diagenesis takes place at temperatures of less than 200 degrees C (392 degrees F); at higher temperatures, scientists say that the rocks are undergoing metamorphism.