When a rock crystallizes from melt (magma or lava), it is an igneous rock.
This rock can be weathered and eroded, then redeposited and lithified into a sedimentary rock.
Advances in seismology, computer modeling, and mineralogy and crystallography at high temperatures and pressures give insights into the internal composition and structure of the Earth.
At the later end of the scale, it is marked by the present day (in the Holocene epoch).
There are three major types of rock: igneous, sedimentary, and metamorphic.
The rock cycle illustrates the relationships among them (see diagram).
They also provided a driving force for crustal deformation, and a new setting for the observations of structural geology.
The power of the theory of plate tectonics lies in its ability to combine all of these observations into a single theory of how the lithosphere moves over the convecting mantle.