Thermal history of the Earth - Why does Earth have a plate tectonic system?
Was it hot or cold when it first formed? Probably cold.
In any case it must have heated up due to:
-solar luminosity which was greater early in solar system formation
-gravitational energy of accreting particles converted to heat
-need only bodies up to 300 km impacting to get major early melting
-gravitational energy of core formation
-heat generated by decay of abundant radioactive elements. Many, for example 26Al, are no longer around today
-maybe tidal friction cause by attraction of the moon
Evidence the earth must have heated up
- internal stratification - determined from density distribution (from gravity measurements)
- moment of inertia studies
- earthquake wave evidence
- composition of meteorites
Once heat is buried it stays in there for a long time because rocks conduct heat poorly.
Heat is transported by:
conduction
radiation
convection
Most of the transport of heat from the interior to the surface of Earth is by convection. The solid but hot rocks gradually flow since hot rocks are less dense they rise, while cold more dense rocks sink. These currents move heat from the interior of Earth to the surface.
Find out more about the THE HEAT HISTORY OF THE EARTH