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Trains, now on Uber. T's and C's apply. Check the Uber app. This is Scientific American 60 Second Science.

I'm Julia Rosen.

We all know the story.

66 million years ago, a giant asteroid crashed into Earth

killing off three quarters of all species including most of the dinosaurs.

Researchers suspect that the impact caused the extinction by kicking up a cloud of dust and tiny droplets called aerosols that plunged the planet into something like a nuclear winter.

And these components in the atmosphere drove global cooling and darkness that would have stopped

photosynthesis from occurring, ultimately shutting down the food chain.

Shelby Lyons, a recent PhD graduate from Penn State University.

But scientists have also found lots of soot in the geologic layers deposited immediately

after the asteroid impact, and the soot may have been part of the killing mechanism too

depending on where it came from. Some of the soot probably came from wildfires

that erupted around the planet following the impact but most of these particles would have lingered in the lower

atmosphere for only a few weeks and wouldn't have had much of an effect on global climate. But scientists

hypothesized that soot may also have come from the very rocks that the asteroid

pulverized when it struck. If those rocks contain significant amounts of organic

matter such as the remains of marine organisms, it would have burned up on impact, sending soot shooting up into

the stratosphere. In that case, soot would have spread around the globe in a matter of hours

and stayed there for years, and it would have radically altered Earth's climate. So Lyons and her team

set out to identify the source of the soot. They looked at chemicals known as polycyclic

...