Gilaad Amit: The dominant explanation for why mountains don't keep growing is the glacial buzzsaw hypothesis. He says new research seems to offer an answer, and it's based on evidence of a huge landslide in the Himalayas 800 years ago. Gilaad concludes that similar mechanisms may play an important role in keeping tall mountains just tall, not too tall.
Little is known about why he fled across the border into the hermit kingdom, but securing his release will require some tactical diplomacy. Given the tense relationship between both countries, is Kim Jong Un prepared to come to the table? A look at research which suggests gold might not always be an effective hedge against inflation (08:52). And, why mountains stop growing (15:42).
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