Name: The secret history of dirt
Uploaded: 2020-09-03T18:05:11.000Z
Duration: 10 min 39 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

This is my compost bin. It's where I put used coffee grounds, melon rinds, corn husks;

Adverbs of degree

pretty much anything that was a plant in its former life, along with shredded up newspapers,

junk mail and pizza boxes. If I wait long enough, something kind of amazing happens.

All that stuff is transformed into, well, what looks like ordinary dirt. But this dirt is

anything but ordinary. This dirt is alive. Yes, it's full of earthworms. We'll get

to them. But it's also full of millions of tiny creatures that you need a microscope

to see. You wouldn't know by looking at them, but these little guys hold the key to

human civilization. Without it, human life as we know it wouldn't be possible. Which makes

it all the more puzzling when you discover that its number one enemy is us.

So, not all dirt is created equal. It can have more or less of those little living creatures in it.

And there's an easy way to tell even if you don't have a microscope at home.

First, put about a handful of dirt in a clear glass jar. This is some soil I collected from the worm bin.

Don't worry, I took out the worms later. And this I dug up from my backyard.

Next, add some water. Screw the lids on nice and tight, and shake them up. And now, we wait.

OK, it's been a day, we're back, and we can see that both of our samples have separated

into distinct layers. You can see that they look really different.

Let's look closer at the dirt from the backyard. It has a bunch of stuff

on the bottom: gravel, sand, silt, and clay. This stuff floating at the top is called humus.

That's where all the microscopic creatures live. Scientists call them microfauna: micro

for small, fauna for animals. There are millions of different kinds. When old plants die, the

microfauna eat them and then, well, they poop. That waste is full of nutrients that

new baby plants need to grow. Grass, tomatoes, apple trees--- no matter the plant, the process

is the same. And the more microfauna there are in the soil; eating, pooping, doing their

thing… the bigger and healthier the plants. Over millions of years, the new plants would

use up nutrients in the soil, then the microfauna would replaced those nutrients by eating the

dead plants. In mild climates, the microfauna could build up about two and a half centimeters, or one inch

of humus every 500 years. Evolution continued and eventually produced a species who changed

Homo sapiens have been around for almost 200,000 years, but we didn't

start farming until about 12,000 years ago. Before then, we still depended on healthy

soil for food. The grass that fed the herd animals we hunted,  the nut trees and berry

plants we foraged… these all grew from the rich humus that the microfauna created.

Farming developed at various points in time, in different regions of the world. And from

the beginning, some of those early farmers recognized the relationship between healthy

soil and healthy plants. Like the Iroquois in the eastern part of what is now the United

States. The first farmers there,  women, by the way, planted corn atop mounds of

soil every spring. After they harvested the corn in the fall, they left the dead cornstalks

atop the mound. All winter long, the microfauna broke them down into nutrient-rich humus.

The next spring's new baby corn plants would use those nutrients and start the cycle again.

Iroquois farmers would also plant beans and squash in the same plot. Together, these three

crops were known as the “three sisters.” Not only did this combination make for a balanced

diet of protein, carbohydrates, and crucial vitamins for the Iroquois people, it also

kept the microfauna in the soil happy, healthy and pooping. Early farmers in other parts

of the world developed different ways to feed the soil. Like in the Amazon river basin.

Early farmers there used controlled fires to create patches of rich humus.

Today, if you dig deep into that soil, you can see that its much darker and healthier

All over the world, the earliest farmers found ways to care for the

soil so that it would produce healthy plants. But slowly, as European colonists descended

on various parts of the world, these ancient practices gave way to a new type of farming.

Machines like the steam engine and the power loom transformed life in Europe, and then in North

America, starting in the mid-1700s. The lure of factory wages drew people from the countryside

into cities, which meant the farmers who stayed on the land needed to produce more food to

be shipped to the cities. Farmers got stuck in a cycle of constant harvesting, without

giving the soil time to regenerate the nutrients it had built up over generations. The soil

quickly wore out, so they responded by cutting down forests and turning them into fields.

In North American, European settlers used violence to push the Iroquois and other indigenous people further west,

away from the three sisters fields that had sustained them for thousands of years. When

they stripped that soil of its life, the settlers kept moving west, seizing indigenous lands

along the way. New steel plows helped them break up the hard, heavy soils of the Great

Plains. But these new steel plows did something else. They turned up the soil over and over again, which killed

a lot of those microfauna that had been living in the soil making humus. And when gasoline-powered

tractors showed up in the early 1900s, their weight pressed down on the increasingly lifeless

soil, making it even harder for plants to grow. By the 1930s, the soil of the Great

Plains had lost so much of its microfauna, giant dust storms pummeled the region. Thousands

of families lost their farms. This new type of farming wasn't limited to Europe

and North America. The small farms that had sustained the indigenous peoples of Central

and South America for generations had been replaced by giant mega-farms, haciendas, run

by the Spanish and Portuguese settlers and worked by indigenous and enslaved people.

the crops didn't feed the people there. These fields were full of sugarcane and cotton to

be shipped out of the country to factories. And, just like in North America, the overworked

soil quickly crumbled and started to wash away. In response, farmers around the world

started to rely on chemical fertilizers, which help crops grow quickly, but can also pollute

drinking water and kill fish and other types of aquatic life. According to the United Nations,

practices like this are killing the humus so quickly, we may run out of healthy soil

in less than 60 years. That is, if we keep doing things the same way.

Remember the soil we tested, that these guys helped to make?

Look at it next to the jar of backyard soil. See how there's way more humus floating on the top? More of this stuff is exactly

what we need, all over the world, to replace the soil we've already destroyed.

On farms where years of plowing has damaged the soil, a handful of farmers have stopped doing it.

Instead, they roll down the old crop then use a series of drills to plant the new seeds

underneath the old crop. Because this method doesn't disturb the soil, it gives earthworms

a chance to make humus, and to create tunnels that help water get to plant roots. It also

helps to loosen the soil so that plant roots can spread. But this method has been slow

to catch on. Just one in four American farmers use it. On many smaller farms, though, earthworms

are a big part of the operation. This is our worm bin. These are the hardest workers, these

are actually red wriggler worms. This is Marc White. He showed me around his urban farm,

right in the middle of Cleveland, Ohio.Here are the raspberries I talked about. Just pull

one off right there. Oh my gosh. Isn't that awesome? Everything is based on the soil. Everything that

On Marc's farm, that process starts here, in the compost

pile. Over time, wood chips and food waste break down with the help of earthworms and

So this is how the soil you saw inside, this is how it starts out.

In the next 10, 15, 20 years, this whole footprint will have been improved so much more for us

We need healthy soil to grow healthy food, and we need healthy food

to grow healthy people. It's all connected.Dirt is so much more than the stuff beneath our