Earlier this year, Nicole Yamase explored the bottom of the Challenger Deep, the deepest place in the ocean, where few people have ever been. The rest of the seafloor is almost as mysterious — 80 percent remains unmapped — but the few glimpses scientists have gotten have completely revolutionized our understanding of the planet. For more, go to http://vox.com/unexplainable It’s a great place to sign up for our newsletter, view show transcripts, and read more about the topics on our show. Also, email us! unexplainable@vox.com We read every email. Support Unexplainable by making a financial contribution to Vox! bit.ly/givepodcasts Learn more about your ad choices. Visit podcastchoices.com/adchoices