We are in the middle of what some scientists are calling the sixth mass extinction and not all at-risk species can be saved. That’s causing some conservationists to say we need to start thinking about “species triage.” Meagan Cantwell interviews freelance journalist Warren Cornwall about his story on weighing the costs of saving Canada’s endangered caribou and the debate among conservationists on new approaches to conservation.

And host Sarah Crespi interviews Hope Michelsen, a staff scientist at Sandia National Laboratories in Livermore, California, about mysterious origins of soot. The black dust has been around since fire itself, but researchers never knew how the high-energy environment of a flame can produce it—until now. Michelsen walks Sarah through the radical chemistry of soot formation—including its formation of free radicals—and discusses soot’s many roles in industry, the environment, and even interstellar space.

Check out this useful graphic describing the soot inception process in the related commentary article.

This week’s episode was edited by Podigy.

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[Image: Darren Bertram/Flickr; Music: Jeffrey Cook]