Comparatively, we know an awful lot about life on the surface of planet earth. We know a lot less about the extent of life in our oceans, and we know even less about the life festering deep beneath us, in the rocks underground. Scientists estimate that 20% of the earth's biomass (that's the combined weight of all living things) are beneath our feet - microbes adapted to the extreme temperature and pressure down there. Geologists, like Andy Mitchell from the University of Aberystwyth, are determined to understand more about these microorganisms, and not just for scientific interest. If we are... Like this podcast? Please help us by supporting the Naked Scientists