BRAINS TRUST – Soil

What is soil?

About 95 percent of soil is crushed rock minerals (crystals of sand, silt and clay), about five percent is organic matter (things that have been alive at some point), and about 0.5–1 percent is living microbes. Up to 25 percent of living soil is air, by volume, and vital for healthy soil.

How is soil made?

Lichens, fungi, worms and microbes can help break down rock, but most comes from other actions such as freezing and thawing, glaciers or gradual erosion. Organic matter comes from leaf matter and animals – so dead roots, leaves and the like, along with insects, microbes and so on.

Plants feed the underground ecosystem with sugars and other organic compounds, essentially pushing organic matter into the soil because they can construct carbohydrates through photosynthesis. Nature makes soil at a similar rate to it being lost, but humans have typically degraded soil faster than it is made.