Deep in the hyperarid core of the Atacama Desert, where less than 2 millimeters of rain falls in a year, scientists have rewritten the timeline of Earth's driest region—pushing its extreme aridity back 20 million years earlier than anyone previously thought. A collaborative study from the University of Cologne and SUERC Centre for the Isotope Sciences, published in Nature Communications, reveals that the Atacama's hyperarid conditions began over 40 million years ago, not 15 to 20 million years as the scientific consensus long held. The discovery transforms our understanding of how deserts form and offers crucial insights into how life adapts—or fails to—in Earth's most inhospitable places.
For decades, researchers believed the Atacama Desert took shape during the Early to Mid-Miocene period, shaped by changing ocean currents and the formation of the Andes mountain chain. But Dr. Benedikt Ritter-Prinz of the University of Cologne and his team found evidence suggesting something deeper happened much earlier. The extreme dryness appears to have coincided with a period of global cooling that followed the Early Eocene Climate Optimum, a brief warm period that ended around 40 million years ago. This suggests that the mechanisms scientists once credited with creating the desert—shifting currents and mountain building—may have only intensified conditions that were already taking hold.
The breakthrough came from an ingenious method: analyzing cosmogenic nuclides in quartz pebbles scattered across the desert's flat surfaces. These rare isotopes form when high-energy cosmic rays strike minerals at Earth's surface, and their concentrations reveal how long a landscape has remained undisturbed. Using high-sensitivity mass spectrometers at SUERC in East Kilbride, researchers measured isotopes called 21Ne and 10Be in countless pebbles. The extraordinarily high concentrations they found pointed to one conclusion: these surfaces had stayed largely unchanged for tens of millions of years.
Professor Fin Stuart of SUERC explained the profound simplicity of the finding: in rainy regions, rainfall constantly reshapes the land by eroding rock and moving sediment. But in the Atacama's hyperarid core, almost nothing happens. The landscape becomes frozen in geological time. "The ability to determine the extremely long surface residence of the pebbles provides a new chronometer of long-term climate change," Stuart noted.
This extended timeline matters far beyond academic curiosity. The Atacama, as one of Earth's most water-limited regions, serves as a natural laboratory for understanding life at the absolute edge of habitability. For 40 million years, the desert has been testing the limits of what organisms can endure. Even rare, brief episodes of rainfall in such an environment can leave lasting marks on the landscape and open temporary windows for life to colonize and evolve. Understanding when extreme aridity began helps scientists connect the dots between climate swings, landscape stability, and biological adaptation over deep time.
The soils that eventually developed in the Atacama possess remarkable properties—they absorb weak rainfall and prevent runoff, stabilizing the landscape further in a positive feedback loop. This hyperaridity, it turns out, paradoxically creates conditions for its own persistence. The new chronology reveals just how long this frozen, dormant landscape has endured, and opens fresh questions about how Earth's extremes shape the boundaries of life itself.