## The Pot of Gold at the Centre of the Earth

The density of the Earth is not constant. The lightest elements, or the elements that form gases, form the Earth's atmosphere. The density of the Earth's atmosphere at sea level is about
$1.29 kg/m^3$
. At the top of the Earth's atmosphere the density is very low indeed. The next density part of the Earth is the oceans. The density of pure water is
$1000 kg/m^3$
. The Earth's ocean contain dissolved substances - mostly salt and some gases. The density of the oceans is about
$1030 kg/m^3$
.
The solid parts is the Earth - the crust - is much denser than water. The crust has a density of about
$2,700 kg/m^3$
, and below this is the Earth's upper mantle with a density of
$3,400 kg/m^3$
and the Earth's lower mantle with a density of
$4,400kg/m^3$
. Then there is the Earth's outer core with a density of
$9,800kg/m^3$
and the inner core with a density of
$12,100kg/^3$
.
The density of gold is
$19,300 kg/m^3$
. Solid gold is the eighth densest element, and all the elements denser than gold are quite uncommon. It follows that gold should sink to the centre of the Earth and the Earth should have a gold rich core. Unfortunately, we cannot mine to gold and become rich We would have to drill through 100km of rock, then thousands of km of molten rock. If we can reach the core, where the temperature is about 6,300 Degrees Kelvin, are the drilling tools would be melted 