The Atacama Desert in northern Chile is the driest place on Earth, a parched rockscape whose inner core supports zero animal or plant life. Only a few hearty species of lichen, algae, fungi, and bacteria can survive there—mostly by clinging to mineral and salt deposits that concentrate moisture for them. Still, it’s a precarious life, and these microbes often enter states of suspended animation during dry spells, waking up only when they have enough water to get by.
So when a few rainstorms swept through the Atacama recently, drenching some places for the first time in recorded history, it looked like a great opportunity for the microbes. Deserts often bloom at such times, and the periphery of the Atacama (which can support a little plant life) was no exception: It exploded with wildflowers. A similar blossoming seemed likely for the microbes in the core: They could drink their fill at last and multiply like mad.
Things didn’t quite work out that way. What should have been a blessing turned into a massacre, as the excess water overwhelmed the microbes and burst their membranes open—an unexpected twist that could have deep implications for life on Mars and other planets.
The Atacama has been arid for 150 million years, making it the oldest desert on Earth. Its utter lack of rain can be traced to a perfect storm of geographic factors. A cold current in the nearby Pacific Ocean creates a permanent temperature inversion offshore, which discourages rainclouds from forming. The desert also lies in a valley that’s wedged between the Andes Mountains on the east and the Chilean Coastal Range on the west. These mountains form a double “rain shadow” and block moisture from reaching the Atacama from either side. The desert’s driest point, the Yungay region, receives fewer than 0.04 inches (or 1 millimeter) of rain a year. Death Valley in California gets 50 times more rain annually, and even the driest stretch ever recorded there still averaged 0.2 inches a year.