If the surface area of the Earth is 5.1 x 10^8 km2, and it increases its radius by
0.908 cm per year ( 9.08 X 10 ^ -6 km) , 4540 km3 of rock material are added each
This new material comprises predominantly of basalt which forms at mid-ocean ridges.
Basalt weighs 3011 kgs per m3 = 3.0 x 10^12 kg/km3
1.36 x 10^16 kg of basalt are produced each year
An estimate of the heat of formation of this quantity of basaltic rock
If we consider basalt is predominantly formed from silica, we know that silica has
a molar mass of 60.8 gm/mol.
In 1.36 x 10^16 kg of basalt there are 1.36 x 10^16 / 0.060 mols
= 2.2 x 10 ^17 mol
The heat of Formation of silica is -910.9 kJ/mol
So the heat of formation in 2.2 x 10^17 mol is
2.0 x 10^23 joules
Or 0.2 Zettajoules
Or 1 million times the energy released in the Hiroshima nuclear blast.
So 0.2 Zettajoules of energy are given out in the exothermic reaction between silicon
ions and oxygen ions as they combine. This keeps the mantle hot, it causes the high
hydrostatic pressures of the mantle against the undersurfaces of the crust, or the
extrusion of magma through fissures in the Earth’s crust.