The mantle?composed of solid and dense rocks-
is the largest layer of Earth. 2,900 kilometers
(1,800 miles) thick, it makes up about 83% in volume
and 67% in weight of our planet. Within Earth's outer
crust rocks remain rigid. Deeper, the temperatures
and pressures increase until rocks soften and deform.
On this viscous material, the crustal tectonic plates
slide and collide over millions of years, forming new
seafloor, building continents, and causing great
earthquakes as crust sinks back into the mantle.
These slow movements also exchange important
substances-including water, carbon, and oxygen-
among the deep Earth, ocean, atmosphere,and even
Illustration demonstrating some of the most important underlying crustal processes that formed and continue to
shape our planet's surface and crustal geology. Great strides in our understanding of these crustal processes will
be achieved by studying the nature and composition of directly sampled deep crust and mantle material up-to and
beyond the Moho (figure courtesy of Smith-Duque C.E).