How the biggest hot desert helps the biggest rainforest grow.
🌍 Play this lesson on the globe
The Sahara is the biggest hot desert on Earth. The Amazon is the biggest rainforest. An ocean lies between them, yet the desert helps the forest grow. How?
One of the dustiest places on Earth is the Bodélé Depression in Chad, in the middle of the Sahara. By one estimate, about half of all the dust that leaves the Sahara comes from here. Long ago it was the bottom of a giant lake, and now the wind blows the dried-up lake bed away.
Strong winds lift the dust high into the sky. Then the wind carries it west, right across the Atlantic Ocean. From space, it looks like a long yellow-orange haze over the blue sea.
The dust doesn’t always take the same road. Its path moves north and south with the seasons. Drag the Month slider and see where the dust ends up. (The paths are drawn by hand, so they’re simplified.)
On the way, some dust falls into the sea or gets washed out of the sky by rain. But every year, on average, 27.7 million tons lands on the Amazon: enough to fill more than 100,000 big trucks! Even more, about 43 million tons, goes on to the Caribbean.
The dust carries phosphorus, a plant food. The Amazon’s soil has very little, and heavy rain keeps washing it into the rivers. The dust brings about 22,000 tons of phosphorus a year, about as much as the rain washes away!
The dust does more on its trip. Its hot, dry air can stop hurricanes from growing, and in the sea it feeds tiny floating plants called plankton. When it reaches the USA, it makes hazy skies and bright sunsets.
The Sahara’s dust comes from many places. But by one estimate, about half of it blows out of one dried-up lake bed, north-east of Lake Chad.
🌍 Play this lesson on the globe
The globe pictures are simplified to show the idea. Earth images: NASA Blue Marble (public domain).