Read: Climate change is hurting desert life

That’s why the recent rainstorms in the Atacama—two in 2015 and one in 2017—were so startling. They left behind standing lagoons, some of which glowed a lurid yellow-green from the high concentration of dissolved mineral. Nothing like this had happened in Yungay since at least the days of Columbus, and possibly much earlier. No one quite knows what caused the freak storms, but climate change is a likely culprit, as the cold sea currents have been disrupted recently. This allowed a bank of rainclouds to form over the Pacific Ocean. The clouds then plowed over the Chilean Coastal Range and dumped water onto Yungay and surrounding areas.

Five months after the June 2017 storm, a group of scientists led by Armando Azua-Bustos, a microbiologist at the Universidad Autónoma de Chile, and Alberto Fairén, a planetary scientist at Cornell University, visited the Atacama to sample three lagoons. They wanted to study the microbes that had gotten swept into them and document how well they were handling this precious influx of water.

Not very well, it turned out. As detailed in a recent paper, the scientists found that the majority of microbes normally present in the soil had been wiped out—14 of 16 species in one lagoon (88 percent), and 12 of 16 in the others (75 percent)—leaving behind just a handful of survivors. On a local scale, the rains were every bit as devastating as the asteroid that wiped out the dinosaurs 66 million years ago, which killed off 70 to 80 percent of species globally.

The scientists traced this massacre back to the very thing that allows the microbes to survive in the Atacama: their ability to hoard water. Under normal conditions, this miserliness pays off. But when faced with a glut of water, they can’t turn off their molecular machinery and say when. They keep guzzling and guzzling, until they burst from internal pressure. Azua-Bustos and Fairén’s team found evidence of this in the lagoons, which had enzymes and other organic bits floating around in them—the exploded guts of dead microbes.

Water in the Atacama, then, plays a paradoxical role: It’s both the limiting factor for life as well as the cause of local extinctions. And while the death of some bacteria and algae might not seem like a big deal, these microbes are actually famous in some circles as analogues for life on Mars.

We don’t know whether Mars ever had life, but it seemed like a promising habitat for its first billion years, with vast liquid oceans and plenty of mineral nutrients—not much different than Earth. One billion years probably wasn’t enough time for multicellular life to arise, but Martian microbes were a real possibility.