There are many types of soil around the world.
Healthy soil has a good combination of soil structure, chemistry, organic matter content, biology and water permeation for its type.
A typically healthy soil will be teeming with biodiversity and may include a variety of earthworms, 20-30 types of small arachnids, 50-100 species of insects, hundreds of different fungi and thousands of bacteria species.
'There are some things in soils which will be visible to the naked eye, like invertebrates and plant roots,' explains Silvia. 'But there are also millions of things people won't be able to see like micro-organisms and all the fascinating work they do together.'