More than 60 million years ago, an object the size of a small city barreled into planet Earth, traveling at more than 22,000 miles per hour.

That meteoroid, many scientists believe, triggered a set of cataclysmic climate changes and natural disasters that led to the extinction of the dinosaurs. But what triggered the meteoroid?

Lisa Randall, a particle physicist and bestselling author, tackles this question in her book, "Dark Matter and the Dinosaurs: The Astounding Interconnectedness of the Universe."

Randall theorizes that the meteoroid was a comet that was dislodged from its orbit when the solar system passed through a disc of dark matter.

If you're now wondering, "what's dark matter?", you're not alone. Dark matter is one of the great mysteries of modern science.

Dark matter acts like matter, Randall said, "but what distinguishes it is that light just goes right through it. ... I wouldn't call it dark — I would call it transparent."

"Billions of dark matter particles are going through us every second, but we don't know it because they're not interacting with us."

In 2015, Randall joined MPR News host Kerri Miller to talk about her dark matter research and other mysteries of the universe. Let it whet your appetite for the conversation with novelist Emily St. John Mandel coming this Friday, which explores time travel in a futuristic world.

Guest:

• Lisa Randall is a best-selling author and Harvard astrophysicist.

To listen to the full conversation you can use the audio player above. 

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