Dust in the Wind: A Hidden Miracle

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Dust blown from the Sahara Desert crosses the Atlantic Ocean to fertilize the Amazon rain forest.

Ah, so you’ve heard this one before! 

sahara arid dune

 

Good because that’s not the interesting part.

Scientists have been stumped as to how it is that dust from one of the most nutrient poor places on Earth was acting as fertilizer.

If I pour sand on my garden it’s going to have a bad time; the Sahara Desert isn’t made of Miracle Grow, afterall.

Amazon luscious lake

New satellite data finally cracked this mystery. As it turns out, a tiny, nutrient rich bowl that makes up less than 1/500th of the Sahara Desert produces over half the dust blown to the Amazon.The other 99.8% of the Sahara Desert combined produces less dust than this tiny area.

This is like pouring a bowl of Lucky Charms and getting 99% marshmallows every time you pour a bowl. A miracle in its own right.

(Satellite image of sources of trans-Atlantic dust)

Africa dust map

The dust from the other 99.8% of the Sahara Desert is nutrient poor, and would do little to fertilize the Amazon, so how is it that 50% of the dust kicked across the Atlantic comes from just 0.2% of the Sahara Desert?

Bodélé Depression from space

The winds hitting this area, called the Bodele Depression, are unusually strong jet stream winds that are completely absent in the rest of the Sahara. A strange funneling effect happens on a massive scale as the jet stream gets squeezed through the Tibesti Mountains and Ennedi Massif upon entering the former plains of Mega-Chad Lake.

This causes massive amounts of nutrient rich sediments to get pushed high into the atmosphere and carried thousands of miles across the Atlantic.

bodele depression geography

The Bodele Depression is a remnant of the world’s largest freshwater lake. Just a few thousand years ago Mega-Chad Lake was ~140,000 square miles; for comparison, Lake Superior, the world’s largest freshwater lake today, is just 32,000 square miles.

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Today all that remains of this enormous lake is Lake Chad. Soon even this whisper of a grander past will vanish – Lake Chad has shrunk by 95% in just the last 50 years. This is highly unfortunate as 30 million people rely on its water for drinking and irrigation.

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The Bodele Depression’s dried lake bed surface is composed of layer upon layer of the phosphorous, nitrogen, and iron rich remains of plankton. This plankton was deposited long before the lake existed; over 100 million years ago this depression was part of the ocean, and for millions of years plankton lived, died, and sank to the bottom to produce these nutrient rich layers.

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There is one more factor that makes this an incredibly serendipitous situation. Not only is the Bodele Depression nutrient rich, but it is rich in the exact nutrients that the Amazon needs.

Plants need numerous nutrients to grow; only by feeding them the select few they are short on can they benefit from it. If a plant is short on Manganese and you give it Iron you’re more likely to harm it, much less help it.

The Amazon rainforest’s soil has very little phosphorous. In fact, it has so little that phosphorous is the limiting factor in plant growth. Even though there are abundant amounts of other “fertilizers” the plants can’t grow once they hit the wall of depleted phosphorous.

Amazon Wildcat

Well it just so happens that the dust from the Bodele Depression is particularly rich in phosphorous. As it crosses the Atlantic the phosphorous dissolves into the water droplets that fall to the ground in the Amazon’s frequent downpours. The Amazon’s rain is literally a liquid fertilizer enriched with the exact ratio of nutrients that it needs.

What a tale indeed!

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Life living in an ancient ocean stored just the right ratio of nutrients for a rainforest thousands of miles away that wouldn’t exist for another 100 million years. Those nutrients then traverse an entire ocean due to a near impossible funneling of a jet stream through just the right geographic features. An event so improbable that it results in just 0.2% of the Sahara Desert producing more dust than the other 99.8%.

Truly remarkable.

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Perspective: Light From 10 Billion Years Ago Hits Us Today

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This week, an entire new class of Supernova was discovered by analyzing light from a star that exploded 10 billion years ago.

A 300-year-old supernova remnant created by the explosion of a massive star.

This means a single photon of light began its journey to our eyes 10 billion years ago. It was created in the crucible of the most powerful explosion in the universe – over 100 times more powerful than the previous record-holder.

The power of the previous record? Several octillion (it’s a real number I swear) nuclear warheads igniting in synchrony.

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The majority of the life of the universe unfolded during this photons travels. It traveled through dust clouds birthing stars, across entire galaxies, surviving the vast, empty, cold void between galaxies for 10 billion years before ending its life by traveling through your tiny pupil, and exciting nerves in your cornea.

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The supernovae exploded when the universe was only 4 billion years old. “This happened before the sun even existed,” Howell explained. “There was another star here that died and whose gas cloud formed the sun and Earth. Life evolved, the dinosaurs evolved and humans evolved and invented telescopes, which we were lucky to be pointing in the right place when the photons hit Earth after their 10-billion-year journey.”

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Civilization: The Blink of a Galactic Eye

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It takes our solar system approximately 240 million years to orbit the Milky Way Galaxy, an event known as a galactic year.

If you went back just one galactic year, then flowers would not yet exist; in fact, you would still have to wait another 100 million years before the first flower bloomed.

 Extinction of the dinosaurs, artwork

Dinosaurs had life pretty good for 135 million years (~½ a galactic year) before an extinction event carved the way forward for mammals and birds to proliferate. Humans have existed for 1/100 of a single galactic year, and agriculture has existed for 0.0000417 galactic years.

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What will the biological diversity of Earth look like when it returns to its current celestial position? Dinosaurs, flowering plants, birds, and mammals had yet to evolve 1 galactic year ago, and the entirety of agricultural history has existed for the equivalent of 22 galactic minutes, or 0.015 galactic days.

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