for National Geographic News
Microbes can traverse oceans and continents by hitching rides on minute dust particles, scientists report.
By analyzing dust samples originally collected by naturalist Charles Darwin, researchers have determined that bacteria and tiny fungi originating in the western Sahara desert are also found as far away as North America and the Caribbean.
Swirling windstorms in northern Chad sweep up sands from the Sahara, carrying the smallest particles into the troposphere, 1 to 6 miles (2 to 10 kilometers) above Earth's surface.
The fine grains are then blown across the Atlantic Ocean, settling nearly 6,200 miles (10,000 kilometers) away.
Anna Gorbushina and William Broughton at Switzerland's University of Geneva had long been interested in what the dust carried on its intercontinental travels.
"We've known about this phenomenon for centuries," Broughton said.
But not enough of the dust was available for study until a colleague suggested testing Darwin's samples, he explained.
Their team's findings appear in the current issue of Environmental Microbiology.
In the early 1800s, Darwin and others collected some of this aerial dust from Barbados and while at sea in the Atlantic Ocean.
Using only the most abundant samples, the authors employed geochemical analyses to confirm that Darwin's collections contained dust originating in West Africa.
In addition the team also found that the dust particles were carrying microbial hitchhikers.
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