Objectives of this chapter

The global energy budget drawn in Chapter 8 and geological evidence indicate that the Earth has been cooling down for several billions of years. We have many reasons to believe that the Earth was very hot after the giant impact and formation of the core. We discuss how the very young Earth might have cooled down rapidly, allowing continents to become stable and grow. We evaluate how to relate the present rate of energy loss to long-term thermal evolution of the mantle, and we discuss the impact of continental growth and the super-continent cycle on the Earth's thermal evolution.

Initial conditions

The Earth is presently in a regime which can be described as one of sub-solidus convection, such that motions predominantly occur in the solid state and depend on the rheological properties of mantle rocks. Melting only occurs at shallow levels and is thought to be a passive process that does not affect large-scale mantle dynamics. In the early stages of Earth's evolution, large amounts of energy were available and probably led to a planet that was almost entirely molten. A host of processes with different dynamics were active then, which may be separated into three categories: accretion, core formation and magma ocean crystallization.

Accretion of the Earth. Differentiation of the core

The accretion process of Earth brought together matter which was originally dispersed in the proto-solar nebula, thereby releasing gravitational energy.