On a recent morning, Noah Fierer, a professor of ecology and evolutionary biology at the University of Colorado, Boulder, found himself standing 1,000 feet above the farmland of eastern Colorado. He was perched near the pinnacle of the Boulder Atmospheric Observatory, a cellphone-tower-like spire built in 1977 to conduct climate and weather research. To reach the top, Fierer and his colleague Joanne Emerson had taken a five-minute ride in the tower’s cramped elevator to an even more cramped catwalk 90 stories up. Dressed in hard hats and safety harnesses, the two leaned over to check a small device strapped to a latticework platform. The machine, which they’d installed several months earlier, sucked in air every night, filtered it, and stored the contents for collection every two weeks. It was basically a vacuum cleaner but instead of hoovering up dirt, it captured microbes.