dirt.

Maybe that's because, most of the time, soil takes care of itself; decomposing plants and

animals and degrading bedrock produce new soil at roughly the same pace that wind and

water erode it away

But this balance between soil formation and erosion is easily tipped.

For millennia, the tiny Pacific island of Mangaia was covered in a thin layer of fertile

soil, but after humans arrived around 2000 years ago, their slash-and-burn agriculture

exposed the soil to the elements.

Over several centuries, rain and wind swept virtually all the nutrient-rich topsoil from

Mangaia's hillsides and concentrated it in just a few arable valleys, which people

viciously fought over.

With less land to grow crops, people resorted to alternative food sources like rats—and

even each other.

We're doing the same thing throughout the world today - not the part where we eat each

other, but the part where we farm the soil away.

That's because we make for agriculture by clearing away deep-rooted native vegetation

and use hoes, plows, and tractors to loosen the soil, making it easier for wind and rain

to sweep away.

And we grow mostly shallow-rooted crops that are no good at holding onto soil, and that

get stripped away during harvest, leaving fields bare for much of the year and at the

mercy of the elements

As a result, the world's farmlands lose soil 50 times faster than new soil can form.

That extra erosion adds up to about 8 billion pickup trucks of soil moved annually from

fields to places like the bottoms of rivers and behind dams - which are less convenient

for farming.

That soil loss reduces global crop yields by as much as if we took a California-sized

swath of farmland out of production every decade.

Fortunately, we know how to bring erosion back into balance with the rate at which soil

forms: plow less often, and after harvest, leave plant parts behind or plant so-called

cover crops to, well, cover the soil as protection against water and wind.

We can also incorporate trees or native plants that keep soil in place year-round.

Putting strategies like these in place can cut erosion by as much as 95 percent, helping

keep crop yields high in the long run.

But in the present, they can hurt yields, because adding other vegetation to farm fields

means less room for crops.

As a result, we've been slow to make these soil-saving strategies the norm.

If we can't keep the farmable soil on our farms, human civilization won't immediately

implode, but we might end up fighting over the patches of land where that soil ends up,

like the Mangaians, but on much, much bigger islands.

And, speaking of soil, this video was sponsored by Soylent, a line of nutritionally-complete,

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Plus Soylent has partnered with the World Food Program USA to donate a meal to someone

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