The Amazon rainforest covers 40% of South America, contains nearly 400 billion trees, and creates one-fifth of our planet’s oxygen.

The river basin feeding the mighty Amazon carries one-fifth of Earth’s river water into the Atlantic ocean every day.

This water adds enough mass to the continent that it distorts the gravitational field over South America.

But the river at the center of this is NOT the biggest river on Earth.

There’s one that’s even bigger…, but it’s invisible, flying around in the sky.

I promise I haven’t lost my mind.

Hey smart people!

Joe here.

You can get a clear view of the Amazon basin on Google Earth, but you’d almost never get a clear view if you were actually in space.

Compared to other parts of Earth, it’s always obscured by clouds.

And that’s thanks to 400 billion geysers shooting water into the sky.

Not geysers like those… trees!

When pores on leaves open up during photosynthesis, plants also lose a lot of water.

Like what happens when you suck on a straw, this evaporation pulls water from the roots to the tops of trees, up to 60 meters off the ground.

A large tree in the Amazon can release 1,000 liters of water into the atmosphere every day.

Altogether, trees in the Amazon basin release 20 billion tons of water, or 20 trillion liters, each day, enough to fill 8 million Olympic swimming pools… which I’m pretty sure you can’t really picture, but it’s true.

Boiling that amount of water would require the energy from more than 30,000 hydroelectric power plants like China’s Three Gorges Dam, the largest in the world.

But trees?

They do it all with the power of the sun.

This living water pump creates a “river in the sky” above the Amazon, stretching from the ocean to the Andes, that moves even more water than the Amazon river itself, and the rain this sky river creates is the reason the world’s largest rainforest even exists.

But it takes more than water in the air to make rain.

Even in the driest places on Earth, a cubic meter of air contains a million, million, billion water molecules.

But H2O can’t form droplets on its own – ever.

Much like the plants they nourish, raindrops grow from seeds.

At the heart of every raindrop is a tiny impurity, anything from specks of dust, to salt, pollen, or even chemicals.

Rain seeds give water molecules something to cling to, so they can grow into droplets.

Trillions of these droplets make up every cloud we see, and when they eventually get big enough and heavy enough, they fall.

So that’s rain.

It’s water collecting on little islands of floating sky junk and pixie dust.

But why do some places get so much rain and others get so little?

Because not every place on Earth has the same type, or same number, of rain seeds in the sky.

And that takes us back to the Amazon and all that green stuff.

95% of the of the Amazon’s rain seeds are made by the trees and plants that live there.

Along with water vapor, trees in the Amazon release chemicals that act as super-sticky H2O magnets.

These biogenic volatile organic compounds are how the forest makes its own rain.

The air over the Amazon contains just 300 particles per cubic centimeter, making it some of the cleanest air on Earth.

It’s likely that a couple hundred years ago, before the industrial revolution, most of Earth’s air was that clean, but these days, thanks to pollution, even our cleanest air elsewhere has 2,000 particles per cubic cm.

And while you might think more particles = more rain, that extra stuff in the sky spreads the same amount of water across more seeds, and smaller droplets means fewer fall as rain.

If you live in the US – whether it’s in Big Sky Montana, or crowded LA – there’s probably less rain now than there was a few hundred years ago, just because of the extra stuff in the air.

What’s SUPER cool is when trees need rain – they release different amounts of rain-attracting chemicals, seeding more of their own clouds and rain.

As the water released by the trees condenses into clouds, it lowers nearby air pressure.

This creates the winds that drive this river in the sky from the Atlantic all the way to the Andes.

Without the Amazon’s trees and this continent-wide rain cloud conveyer belt, areas like this would probably be desert, like other regions at the same latitude.

In school, we learn that rain falls on land, makes its way to the ocean, evaporates, moves inland and falls again.

But we never hear about this green ocean–the Amazon–filled with living geysers.

Trees around the globe act like great green pumps responsible for 90% of the water that reaches the atmosphere over the continents.

We don’t usually think of weather as a living system, but these hundreds of billions of trees in the Amazon and elsewhere are an invisible process, more powerful than human engineers could ever design, yet built all the same by the hands of time and evolution, harnessing the sun not only to give animals air to breathe, but to move the element that makes life itself possible.

The Amazon rainforest is often called the “lungs of the planet”, but it feels a little more like the heart, don’t you think?