The make-up of the interior of the planet is a little hard to prove, although scientists and our schoolbooks confidently tell us that the planet gets denser as you go in deeper. The official line also declares that the crust itself only makes up about 1% of the total volume, and it is thought to be about 6km thick under the oceans, and about 30-50km thick where land is present. Inside that crust is a thin layer called the Lithosphere, and that is surrounded by a 3,000 km thick mostly-solid layer called the mantle which makes up about 84% of the Earth's volume. In the very centre of the planet is the core, which is believed to be made up from almost 90% iron - with solid iron in the inner core and liquid iron in the outer core, and some nickel in both sections too - and this section accounts for about 15% of the planets total volume.

Scientists also believe that the inside of our planet is active, and that therefore this creates the volcanoes and movement of the tectonic plates, which cause our continents to move gradually over vast amounts of time. The geological layers which we believe to be present reflect what we think about the make-up of the inside of the other solid planets too, but in reality, humans have only physically been about 4km under the surface (gold mines in South Africa), we have only ever drilled down to a distance of 1.7 km under the seafloor, and our deepest penetration ever by drilling under land was 12.262 km (7.62 miles) down the Kola Superdeep Borehole in Russia.