Geologic dating activity
Transform boundaries, such as the San Andreas Fault system, resulted in widespread powerful earthquakes.
Plate tectonics also has provided a mechanism for Alfred Wegener's theory of continental drift, in which the continents move across the surface of the Earth over geologic time.
Early advances in this field showed the existence of a liquid outer core (where shear waves were not able to propagate) and a dense solid inner core.
These advances led to the development of a layered model of the Earth, with a crust and lithosphere on top, the mantle below (separated within itself by seismic discontinuities at 410 and 660 kilometers), and the outer core and inner core below that.
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.
These studies explain the chemical changes associated with the major seismic discontinuities in the mantle and show the crystallographic structures expected in the inner core of the Earth.
Geology describes the structure of the Earth beneath its surface, and the processes that have shaped that structure.
It also provides tools to determine the relative and absolute ages of rocks found in a given location, and also to describe the histories of those rocks.
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.
The blue blob in the cutaway section is the seismically imaged Farallon Plate, which is subducting beneath North America.