The whole picture of a section of the Earth's lower crust and upper mantle is pieced together from a variety of geochemical data combined with geophysical data obtained by remote sensing. The vertical distribution of different rock types is mapped out. Important boundaries in the deep Earth are located and characterised, primarily between the crust and mantle and between lithosphere and asthenosphere. The time-line of changes to the composition of the lithospheric mantle is also determined. Perhaps the single most important piece of information available about deep Earth is heat flow.
Thermal energy is behind all active geological processes.
It is the source of mantle fluids, the driving force for all tectonic processes and strongly affects the physical properties of the mantle, eg vapour pressure, density and rheology. Another view of the interior of the Earth showing rising plumes of magma. Volcanic activity, destructive as it may be, brings to the surface xenoliths and diamonds as physical evidence from unreachable depths in the lithosphere. Xenoliths are rock fragments from the lithospheric mantle, spanning the geological timescale from Pre-Cambrian to recent. The xenoliths are the green fragments in the black basalt.