January 6, 2020 — One brisk day in April 2013, as he drove with colleagues along the southern coast of Patagonia, Mike Kaplan spotted a geologist’s treasure trove—an active gravel pit with freshly exposed walls. He pulled over, grabbed the backpack full of digging tools stowed in the car trunk and walked into the large hole.
To Kaplan’s south lay the Southern Ocean, stretching toward Antarctica. Strewn around him was evidence of Earth’s most recent ice age: heaps of crushed rock and gravel released by one of the many glaciers that had once covered North and South America. Standing in the pit, Kaplan spotted what he was looking for: a layer of fine gray silt deposited by ice sheets roughly 20,000 years ago.
A geologist at Columbia University in New York, Kaplan has spent over a decade collecting the sediments that make dust, and studying how that dust, launched from earth to air to sea, influences Earth’s climate, past and present. Dozens of intriguing samples have made their way home with him, stowed in his suitcase or shipped in a duct-taped cardboard box. As he scraped the dark gray sediment into a plastic bag, he felt a rush of anticipation. Given the sample’s location, he thought that it might be just what he needed to test an aspect of a controversial idea known as the iron hypothesis.