The Largest River On Earth Is In The Sky

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. [OPEN] 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. [NASA Animation here – showing that motion] 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? Stay curious.