A particle of dust holds many histories. There is the history of its own becoming. Everything in matter exists in a form waiting to be broken. Dust begets dust. The world has twice as much today as it did in the 19th century.
Wind takes advantage of what it entrains. Red dust from India caught in the gales of a tropical cyclone, once bore down upon Australia in an umber hedge so thick it obscured the horizon. A wave of rosy particles reduced, dwarfed, engulfed the ships at sea. In a particularly intense kind of dust storm, a haboob, the particles are carried on an atmospheric gravity current, a massive downdraft generated in the center of a thunderstorm, which often evaporates more moisture than it deposits.
What the wind may carry aloft has profound and mysterious influences far afield. Desert dust is so intimately tied to climate that one does not exist without the other. A dusty period in Asia increases snowfall in California. Dust trapped deep in the Antarctic ice sheets can help us to reconstruct past climates. Over the past 80,000 years, dirt from the windy plains of Patagonia was periodically blown south and deposited onto this icy enclave. The ebb and flow of Chilean and Argentinean glaciers corresponds to dirty lines in the ice cores—the very coldest periods also resulted in the dustiest.
A particle reveals a world much beyond its boundaries. Dust tells the story of the Mayan decline. In the Classic Period, this civilization stretched across the entire Yucatan Peninsula, from the Caribbean Sea to the highlands of Central America. It was a society of cities, of water infrastructure, and managed landscapes. The heartland was situated on the upland spine, a karstic plateau rising above the sea, a rolling landscape interspersed with sinks and depressions. Here, the limiting soil nutrient was phosphorous. Wind-blown dust from the Saharan desert traveled on the cold persistent tails of circumventing airstreams. When it reached the Mexican highlands, this exogenous nourishment was caught by the canopy of old-growth trees and eventually washed into the soil. This process is so efficient—old forests trap fourfold more dust than opened lands—that nearly 25% of the phosphorous in the soil came from Africa.
But in the expansion of the Mayan Empire, most heartland forests were cleared, cut away to make room for settlements and cultivation and the ubiquitous walled orchard gardens. The only trees stood in managed stands, unremarkable buffers that served as living walls between the hinterlands of city-states. With the land reconfigured in this way, and the canopy of great trees lost, the capture of phosphorous dust decreased and the land became degraded, no longer rich in nutrients and supportive of plants.
Dust maps trajectories of change on the earth’s surface, a process captured in particles so small as to be forgotten and swept away. Today, African dust carries with it metals and microbes, persistent organic pollutants and pesticides, and these contaminants fall onto the declining reefs of the Caribbean Ocean. A pathogenic fungus, known to cause sea fan disease and coral mortality in these warm pale waters, originated from Sahel soil in Mali.
It is thought that as much as 40,000 tons of cosmic dust reaches the Earth’s surface with each passing year. Born in the expanding shock waves of a supernova explosion, spewed out by the last heaving groans of a dying cosmos, stardust was fashioned before our solar system was even conceived. When these interstellar dust particles collided, the pressure was so great that graphitic carbon became hexagonal nanodiamonds.
GinaRae LaCerva is a graduate student at the Yale School of Forestry and Environmental Studies. More of her writing can be found at www.disturbancegeography.com. You can follow her on twitter @GinaRaeLC.