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When you eat a tomato from Florida, chances are it was grown in African soil.
But not because someone shipped the dirt over there or anything.
Every year, tons of dust from the Sahara desert is kicked up by dust storms, blasted high
into the sky, and whisked across the Atlantic Ocean on wind currents.
It takes about a week.
Then, it’s hello, Florida.
In fact, our oceans and continents are all linked into this weird, global dust ecosystem.
Whether it’s going from Australia to New Zealand or from Asia to Oregon, the current
estimate, worldwide, is that 3 billion tons of dust move through the atmosphere every
year.
It comes with some powerful, and surprising, global effects, not all of which are good.
But one way or another, this dust is definitely changing our world.
Scientists can track how the dust moves using satellite images or by analyzing soil samples.
The dust in certain regions tends to contain specific kinds or amounts of elements, and
they act kind of like a fingerprint.
So by measuring where those fingerprints turn up, the researchers can see how the dust has
migrated and what its effects are.
A lot of those effects involve ecology.
Like for starters, dust builds soil.
Lots of soil.
Scientists estimate that more than 30% of the soil in Barbados comes from Africa.
And the stuff in the Bahamas and the Florida Keys?
Mostly African imports.
Besides being weird to think about, the dust is also really important.
In fact, without African dust, the vegetation on some Caribbean islands wouldn’t be nearly
so lush.
See, those islands, along with parts of Florida, are mostly built of crusty coral.
When that coral breaks down, it leaves a pile of broken-up calcium — which, on its own,
isn’t that fertile.
But blast over some African dust and voila.
You’ve suddenly got nutrients in your soil, like magnesium, phosphorous, and potassium,
and things get a whole lot greener.
Dust nourishes soil all over the world, too, including in the Amazon rainforest and northern
Hawaiian islands.
So, on your next tropical vacation, you can thank dust for the scenery.
Now, all that might sound great — and it is.
But long-distance dust can also bring less welcome visitors, too, like pesticides and
metals.
For example, mercury made in China gets mixed in with the dust and blows east across the
Pacific.
Scientists have detected it in rivers and from the top of roughly 3 kilometer high at
Mt. Bachelor in Oregon.
They know it’s from China because it has a specific chemical profile, but also because
the mercury only wafts in when the wind blows from the west.
So it’s almost certainly coming from Chinese coal-fired power plants.
Mercury has plenty of ill effects on humans and ecosystems, including birth defects and
reproductive problems, so accumulating more of it in the water or soil isn’t exactly
a great idea.
I mean, it’s not great anywhere in the world, but it’s harder to manage when it’s blowing
all over the place.
Even without mercury, long-distance dust is also linked to problems with asthma and other
respiratory diseases.
That’s because the particles that travel around the world tend to be especially fine
and harmful to lungs.
The dust can pick up some other hitchhikers, too, including live locusts and, most surprisingly,
microbes.
Until around 2000, scientists figured that intense ultraviolet radiation from the sun
would kill anything alive on its way across the ocean.
But they were wrong.
In a 2002 study from the journal American Scientist, researchers used petri dishes to
collect air samples in the Caribbean on an especially dusty day, and soon, microbes grew
in them.
Microbes aren’t always bad, but altogether, about 20% of the ones found in international
dust have been linked to plant and animal diseases.
One microbe from Africa seems to be strongly linked to a disease killing fan coral in the
Caribbean.
Another is the same disease that causes diseases in Florida’s carrots.
Even occasional human pathogens -- like ones linked to urinary tract or respiratory infections
-- can hitch a ride.
The scientists think that the microbes that survive the journey either have dark pigment,
which could act like sunscreen, or float near the bottom of the dust clouds where radiation
isn’t as intense.
Enough attention is paid to these flying microbes that there’s even a name for this field
of research: aeromicrobiology.
Now, flying dust might have a big impact on ecology, but its influence isn’t just linked
to soil or plant diseases.
The dust can also interact with Earth’s weather — like how African dust weakens
hurricanes.
Yeah.
Hurricanes.
As the dust flies through the air, it can darken the clouds.
That reduces how much of the sun’s heat reaches the Atlantic, and keeps the ocean
surface cooler.
That, in turn, suppresses hurricane formation, since warm ocean temperatures fuel the monster
storms.
So more dust equals fewer hurricanes.
This actually happened in 2006, when thick African dust caused the north Atlantic to
cool a third more than usual.
That year, only five hurricanes formed in the Atlantic compared to the 15 the year before
when there was less dust.
So, from fewer hurricanes to flying microbes, the global dust ecosystem is kind of a mixed
bag.
But one way or another, it’s definitely cool.
Scientists are still working out what this vast, global migration of dust really means
— like what it carries, and how, for better or worse, it’s altering our world.
And with more tracking and more experiments, hopefully we’ll find even more of those
weird effects soon.
Thanks for watching this episode of SciShow!
Besides causing problems on Earth, dust can cause even more trouble in space — and in
fact, it’s kind of an astronaut’s worst enemy.
You can learn all about it over at SciShow Space.
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