Mantle convection is likely to have changed over the course of Earth's history. The mantle was probably hotter when the Earth formed, because of the large releases of gravitational energy during its accretion and the separation of the mantle and core. Also the radioactivity that drives the system now would have been stronger in past times, because of radioactive decay. Thus we might expect that mantle convection used to be more vigorous. But how much more vigorous? We can answer that question by building on the understanding we have already established.

It turns out that there may have been changes other than just a slowing down as the mantle cooled. For example, the melting and differentiation that accompanies mantle convection generate compositional density differences, and these may affect the course of the convection. Rheology may also have important effects. In fact there may have been some quite drastic changes in mantle convection, especially in the first half of Earth's history.

The geological record preserved in continents tells us that there have been changes in geological and tectonic processes over the past several billion years. Quite what the tectonic changes were is not yet very clear, but it is clear that the character of fragments of continental crust preserved from 3.5 Gyr ago is different in important ways from more modern crust.