The Earth Contents

1. Structure

Heating and melting contribute additional diversity to the lithosphere (crust)

Additional diversity within the lithosphere occurs by heating rocks at depth, and by melting which allows components to be separated and mobilised from any rock type and mixed with others to form new metamorphic rocks and igneous rocks. Heating produces metamorphic rocks, and melting produces igneous rocks. These are both initiated at depths of only a few kilometres but the crust is typically around 20 km thick. So we should view the lithosphere as consisting of only a thin layer of sediments and sedimentary rocks, very patchy and variable in thickness, below which occur predominantly igneous rocks constituting 95% of the crustal mass.

Basalt pillars, Dartmoor

What are the three main rock types and how are they formed?