It's said that a teaspoon of soil contains more life than all of the humans on earth. Microscopic life that is - bacteria, fungi, protozoa, nematode worms and microarthropods like springtails and mites, but there's increasing evidence that this invisible world, the earth's microbiome, is under threat. Author, biologist and presenter Gillian Burke is fascinated by soil and has fond memories of playing with the ochre-red soils of Kenya. Gillian digs into the science of soil to ask how to get more people to understand and care about this the trillions of organisms that exist beneath our feet in the same way that we do about the malnourished polar bear on an ice-cap or the endangered mountain gorilla, and what are the consequences of doing nothing? Contributors: Dr Colin Averill, senior scientist at ETH Zurich and co-founder of 'Funga' Chris Jones, Woodland Valley Farm Charles Nicholls, The Carbon Community Dr Elaine Ingham, Soil Food Web Dr Elze Hesse, The University of Exeter Produced for BBC Audio in Bristol by Toby Field