Here's an awesome 3D visualisation from NASA that shows how the Sahara Desert helps fertilise the Amazon rainforest even though they're on two different continents that are separated by an entire ocean. The Saharan dust is carried over by wind and the phosphorous in the dust is essential to the Amazon.
It's really neat how the world's largest desert is responsible for creating the world's largest rain forest. It's also interesting that the amount of phosphorus in the sand sent from the Sahara -- 20,000 tonnes -- is about the same amount that the Amazon loses from rain and flooding every year.
In total, about 25 million tonnes of dust is blown over from the Sahara to the Amazon. NASA says that's enough to fill 104,980 semi trucks.