Leonardo da Vinci once said: “We know more about the movement of celestial bodies than about the soil underfoot.”

He was right 500 years ago, and he’s still right today.

That’s partly because the study of space is mysterious and cool, and there really wasn’t much interest in studying dirt. Until recently...

We now know that about 90 percent of all land-based species live in the soil, not on it. Most of these are microscopic, but they’re incredibly plentiful: there are more microbes in a handful of dirt than people on the planet.

And they’re also incredibly important: without soil microbes, plants might not exist.

Plants require nitrogen and other trace elements, and it’s soil bacteria, and the single-celled organisms that eat them, that process these elements into forms that the plants can use.

With this knowledge, agricultural researchers are reintroducing bacteria into depleted soils to increase the health and nutrition of crops.

Most plants also depend on soil fungi, and this relationship is symbiotic.

The fungi penetrate or encase the roots of plants to draw out what they can’t make themselves: sugars from photosynthesis.

In exchange, the fungus filaments stretch deep into the soil, gathering water and nutrients from a volume 100 times greater than the roots could reach on their own.

This fungal network can even join plants together beneath the soil, which allows amazing things to happen—and we’ll talk more about that on another EarthDate.