This is how little we know about the Earth and how it works: a team of scientists from NASA, Oxford, the Weizmann Institute, the University of Maryland, that of Sao Paulo and others have discovered what they call "a remarkable arrangement in nature": that a tiny region of the Sahara desert, the Bodélé depression located northeast of Lake Chad, is the main source of minerals to the Amazon rain forest. From the Environmental Research Letters, a scientific journal:
About 40 million tons of dust are transported annually from the Sahara to the Amazon basin [by winds]. Saharan dust has been proposed to be the main mineral source that fertilizes the Amazon basin, generating a dependence of the health and productivity of the rain forest on dust supply from the Sahara. Here we show that about half of the annual dust supply to the Amazon basin is emitted from a single source: the Bodélé depression located northeast of Lake Chad, approximately 0.5% of the size of the Amazon or 0.2% of the Sahara. Placed in a narrow path between two mountain chains that direct and accelerate the surface winds over the depression, the Bodélé emits dust on 40% of the winter days, averaging more than 0.7 million tons of dust per day.
The soil of the Amazon tropical rainforest is shallow, poor in nutrients and almost without soluble minerals. Heavy rains have washed away the nutrients in the soil obtained from weathered rocks. The rainforest has a short nutrient cycle, and due to the heavy washout, a stable supply of minerals is required to keep the delicate nutrient balance. (...) Aany change in the nutrient supply will convert tropical forests to 'wet deserts'.
The scientists have analyzed satellite data and imagery showing "continuous dust transport across 5000 km from the Saharan sources to the Caribbean Sea and North America in the Northern summer and to the Amazon basin during the Northern winter".