The processes that generate high-quality, fertile topsoil can take centuries. But the world is ploughing through that resource at an alarming rate.
About 40% of the world's land has already been taken over by agriculture, while livestock grazing and expanding urban areas are taking further chunks out of what is left over.
At first glance, it might seem that there is no shortage of mud and dirt around the world. But it's the quality that really counts.