The important role of dust for planet earth

Sahara dust above the Alps, summer of 2013

Loess is a very fine-grained sediment with just some traces of larger sand grains. Loess forms many hundreds of feet thick, very homogenous, deposits, covering almost ten percent of Earth’s surface. On loess, we find the best soils for agricultural production and areas like the Black Sea, China, but also the interior of the United States, are so fertile thanks to this sediment. As loess often lacks any particular sedimentary features, needed to reconstruct its deposition, geologist struggled for a long time to understand how loess deposits formed. British pioneering geologist Charles Lyell speculated in his "The Student's Elements of Geology" (1870) that  loess is loam deposited by rivers:
"In some parts of the valley of the Rhine the accumulation of similar loam, called in Germany "loess," has taken place on an enormous scale [several hundred feet thick]. Its colour is yellowish-grey, and very homogeneous; and Professor Bischoff has ascertained, by analysis, that it agrees in composition with the mud of the Nile.“
Other geologists explained loess as a colluvium, a sediment formed by weathering of older rocks. Only research done by French geologist  P.T. Virlet d´Aoust (1800-1894) and the description of vast loess deposits in China by Austrian geologist Ferdinand von Richthofen (1833-1905), demonstrated that loess is formed by erosion, transport, and deposition by the wind. Modern research shows that phases of loess deposition correlate with the formation of large ice caps in the northern hemisphere. One model explains loess as a direct result of glacial processes. The wind blows out the fine grains from glacial sediments, like moraines or outwash plains, transporting the fine dust many hundreds of miles. This dust, when deposited again, forms the large plains of aeolian, fine-grained sediments. Another model explains loess as windblown material from deserts or arid areas, not necessarily related to glaciers, however a result of wind patterns occurring only during cold, glacial periods. This ancient windblown dust nowadays provides fertile soils to feed billions.
That wind can transport small particles, just some microns large, over vast distance was demonstrated by the aftermath of the Krakatoa eruption. After the volcanic island of Krakatoa exploded in August 1883, the volcanic ash was distributed by atmospheric currents over almost the entire northern hemisphere. Strange sunsets, characterized by an intense red and yellow glow, were described from London, Oslo, New York, and many other cities worldwide. The dust suspended in the higher layers of Earth's atmosphere scattered the sunlight, causing those eerie effects.
But also dust from noncatastrophic events can travel far. Dust from the Sahara desert can be found in thin layers in the glaciers of the Alps. In the summer of 2013 dust from the Sahara transformed the sky above the Alps in a dark yellow haze. Also the recent red sun seen over the United Kingdom was caused by dust, transported by storm Ophelia from lower latitudes,ans soot from the forest fires in Portugal. The dust particles act as condensation nuclei, forming larger droplets of water. The resulting haze partially covers the sun in the sky, scattering certain wavelengths and adsorbing other, the light we see coming from the sun appears red.
Mud- or blood-rain, as described in some medieval manuscripts as signs of the impending end-times, most likely was rain colored by the yellow quartz crystals and rusty grains coming from the Sahara.
Large plumes of dust over the Atlantic Ocean are visible even from space. Estimated 400 to 700 million tons of dust are blown by the wind over the oceans, as much as 20 percent of it reaches the Amazon rainforest, providing phosphorus, potassium, calcium, and iron, essential for plants to grow, to the otherwise nutrient-poor tropical soils. Saharan dust and its iron content is also an important factor in controlling the bloom of marine algae and so the productivity of the oceans. Among other concerns, climate change could also change wind patterns, interrupting the transport of dust, sustaining the lush vegetation of tropical rainforests and the humble, but even more important, microscopic plants in the  seas.

Source: Forbes