Okay, last question...

In my simplistic model of the Earth, you have the crust, the mantle and the core. Does anything live in the core or at the core-mantle interface, and if not, what is the first level/distance from sea level downwards that you start seeing anything living or even getting close to being considered living?

I'm afraid nothing we know of lives below the level of the earth's crust, although we have vey little direct access to anything other than the crust. The deepest hole we have drilled in the Earth is the Kola Borehole http://en.wikipedia.org/wiki/Kola_Superdeep_Borehole. This did not get out of the continental crust. Given the heat in the mantle it is unlikely anything can survive there. However, geophysical tools are our only means of imaging much of the earth below the surface. A number of specialist microbial communities, called the hot, deep biosphere do exist but these all live in the crust.

"Hope is a duty from which palaeontologists are exempt."
David Quammen