Terrestrial life as we know it couldn't exist without soil. Soil, as we know it today, is a layer of minerals, organic matter, liquids, gasses and organisms that not only provides a medium for plant growth, but also modifies the atmosphere, provides a habitat for animals and retains and purifies water.

This kind of soil hasn't always existed, so in order to understand early conditions on land, we first need to understand what can be constituted as a soil and when these first appeared. Is there soil on the Moon? Can soil fossilise?

Since most terrestrial ecosystems are rooted in soil, if we want to understand how life established itself on land, we first need to know how soils form, how they have changed over geological time and which kinds of plants and fungi can live without it.

Joining us in this episode is Dr Ria Mitchell, Experimental Officer in X-ray Computed Tomography at the University of Sheffield, UK.