Just eight percent of Earth’s surface is covered in topsoil -- but that grows 95 percent of our crops.

And healthy plant growth depends on healthy soil. Which depends on a healthy population of soil life.

As noted in an earlier EarthDate, a single handful of healthy soil contains more microbes than the human population of Earth.

And more biodiversity than the entire Amazon. One handful.

Along with microbes, there are fungi, worms, insects, plant roots, and much more. And they all make noise.

Sixty years ago, ecologists began recording the sounds of nature, to understand what species populate different areas – cataloging, for example, the bird, insect, and animal noises of a forest.

But when one curious scientist poked a microphone into the ground, he was blown away.

Turns out soil life makes noises of its own. From grubs chewing on roots, to worms slithering through tunnels, to millipedes’ feet drumming.

In fact, they realized you can tell a lot about soil health simply by listening to it.

Conversely, degraded soils have less active life, and therefore less sound.

Ecologists now monitor soils with a microphone, helping evaluate their resident lifeforms, crop productivity, and the success of soil replenishment programs.

Their discoveries remind us that soil is a vital, living system, worth protecting for its own sake – and ours.