The Driest Non-Polar Desert On Earth Is Actually 20 Million Years Older Than Thought – And It Puts The Sahara To Shame

Most scientists believe the Atacama's hyper-arid conditions emerged around 10 to 20 million years ago, during the Early to Mid-Miocene. However, new research has dramatically pushed back its origin, claiming its extreme conditions appeared approximately 45 million years ago in the Mid- to Late-Eocene.

“Our results indicate that today's hyperarid core of the Atacama Desert has established since the Mid- to Late-Eocene, indicated by extremely low surface activity,” Dr Benedikt Ritter-Prinz from the Institute for Geology & Mineralogy at the University of Cologne, said in a statement. 

“This makes it one of the longest continuously dry regions on Earth and forces us to reconsider how and when such extreme environments develop."

Dr Ritter-Prinz and his team pushed back the origin of the Atacama Desert's extreme dryness by over 20 million years after studying how cosmic rays had interacted with rocks in the region. The technique, known as cosmogenic nuclide exposure dating, looks for concentrations of rare isotopes – like ²¹Ne, a rare stable isotope of neon – that form when certain minerals are blasted by cosmic rays from space.

After analyzing 135 quartz fragments from the desert's deep interior, they found the highest cosmogenic nuclide concentrations of ²¹Ne ever reported, suggesting the surface rocks of the Atacama have sat pretty much undisturbed for tens of millions of years.

“In more temperate regions, precipitation drives erosion and sediment transport, constantly reshaping the landscape,” explains Professor Tibor Dunai, study author from the University of Cologne. 

“In contrast, the Atacama’s hyperarid core, with less than 2 millimetres of annual rainfall, shows extraordinarily slow surface processes. The landscape is effectively preserved over geological timescales."

As per the new study, the Atacama's aridity was kick-started by a period of global cooling after the Early Eocene Climatic Optimum, an extreme warm period in Earth's history when global average temperatures were an incredible 10°C to 14°C (18°F to 25°F) warmer than today. 

The drop in temperatures reduced moisture in the already semi-arid region, turning it into a full-blown desert. Eventually, shifts in tectonic plates and oceanographic changes sealed the deal, locking the desert into this petrified state for millions of years to come.

Today, the conditions of the Atacama Desert remain this way because it's trapped in a "double rain shadow" between two mountain ranges: the Andes Mountains to the east and the Chilean Coast Range to the west. These towering geological hurdles block water vapor from blowing in from the Pacific on one side, and the balmy, humid air drifting from the Amazon basin on the other.

That's not to say it doesn't get any rain at all. When it does, parts of it can burst into fleeting, colorful bloom. This blooming event is often tied to El Niño events, and if current reports are correct, we could be seeing a major El Niño this year.

The Atacama Desert's seemingly timeless nature is a far cry from other great deserts of the world. Think desert and you probably imagine the Sahara, the giant band of sand that cuts off North Africa from the rest of the continent. However, this region is subject to a cyclic transformation driven by shifts in Earth's orbit, causing it to swing from arid to humid roughly every 21,000 years. It is currently in an arid spell, but between 15,000 and 5,000 years ago, it was a green swampland, rich in human cultures and wildlife. If this pattern sticks, it will become a lush landscape once again in another 15,000 years or so. 

The Atacama Desert is not nearly so fickle. It has been largely unchanged for 45 million years and shows no signs of turning anytime soon.

The new study is published in the journal Nature Communications.