By combining these tools, geologists are able to chronicle the geological history of the Earth as a whole, and also to demonstrate the age of the Earth.
Geology provides the primary evidence for plate tectonics, the evolutionary history of life, and the Earth's past climates.
To study all three types of rock, geologists evaluate the minerals of which they are composed.
Each mineral has distinct physical properties, and there are many tests to determine each of them.
The blue blob in the cutaway section is the seismically imaged Farallon Plate, which is subducting beneath North America.
The remnants of this plate on the surface of the Earth are the Juan de Fuca Plate and Explorer Plate, both in the northwestern United States and southwestern Canada, and the Cocos Plate on the west coast of Mexico.
There is an intimate coupling between the movement of the plates on the surface and the convection of the mantle (that is, the heat transfer caused by bulk movement of molecules within fluids).
At the later end of the scale, it is marked by the present day (in the Holocene epoch).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.Seismologists can use the arrival times of seismic waves in reverse to image the interior of the Earth.It can then be turned into a metamorphic rock by heat and pressure that change its mineral content, resulting in a characteristic fabric.All three types may melt again, and when this happens, new magma is formed, from which an igneous rock may once more crystallize.