What the Wasteland Saw: A Tail of ResiliencePosted: November 27, 2013
Life is scarce here in the heart of the Atacama Desert. Nothing grows. Rain calls twice a century, and never leaves a message. This is one of the world’s most desiccated landscapes, a 600-mile strip along Chile’s western coast that stretches from the Pacific Ocean to the Andes Mountains. And, oh yeah: It’s been this way for about 150 million years.
If you were an early colonizer of the Americas, making your way down from the Bering Land Strait during the Last Ice Age, the Atacama would have loomed before you as a stretch of pure wasteland. No food, no shade, no water: this would be the place to avoid. You’d be better off traveling down the coast, or even braving the highlands of the cooler Altiplano to the east. That’s why, when archaeologists go out looking for early human settlements, they tend to write off this barren deathtrap. Harsh and inhospitable, they say, the Atacama was a barrier to life.
But was it?
This October, a group of South American researchers reported one of the oldest known settlements on the continent: Quebrada Maní, which translates to “Peanut Canyon,” right in the heart of the desert. Excavating the site revealed an intact fireplace, shards of obsidian, opals, and shells dating back 13,000 years. At that time, the Atacama was still a dry, barren expanse, the researchers wrote in the journal Quaternary Science Reviews. But somehow, life found a way. How?
Well, it wasn’t exactly a wasteland. This particular patch of desert was once green with willows and reeds, alive with the trickle of water. Remains of ancient vegetation revealed marshy wetlands, borne of groundwater upwellings and water that flowed down from the nearby Andes. “Picture an oasis in the middle of the Sahara desert,” says Claudio Latorre, a paleoecologist at the Pontifical Catholic University of Chile who co-authored the paper.
The oasis was just one of many that punctuated the parched plateau. “This is kind of the irony of it,” Latorre says. “People were thinking the Atacama desert was a barrier. Now we know that the Atacama was probably a much more favorable place to go through that area than the Altiplano, which was probably a freezer.”
Today’s Atacama, by contrast, is so harsh and inhospitable that NASA uses it as an analog for the red planet, testing its Mars rovers here. When the wind blows, the desert sheds her skin; a layer of fine yellow dust known as chusca lifts up from the ground, forming billowing clouds that choke people and clog trucks. It’s a landscape so oppressive, it has proved a barrier, too, to archaeologists.
Quebrada Maní shed new light on how humans conquered the landscape, providing a crucial link in the chain of settlements showing routes of early migration in South America. (The oldest was Monte Verde in southern Chile, which radiocarbon dating shows to be 14,500 years old.) Now we know that people likely traveled down the western coast in boats, hopping from oasis to oasis.
The settlers of Quebrada Maní had been mobile and resourceful, evidence showed. Excavators found obsidian from the high Andes and seashells from the Pacific—over 80 kilometers away—revealing that they had traded far and wide. They had used the landscape to their advantage, living in hollows in the earth that protected them from the harsh winds. (After the site was occupied, chusca filled the hollows, perfectly preserving the artifacts researchers would later unearth).
Everyone loves a story of human resilience. In October, South American news outlets and the international science community clambered to tell the tale of Quebrada Maní. But the news reports left out a key player.
For thousands of years, he too has navigated the desert. He scales the most barren of rock faces, clinging with long curved claws. To avoid the harsh desert sun, he makes appearances only at night. Twitchy and agile, with glossy gray fur and round Dumbo ears, he is perfectly adapted to this harshest of landscapes. He is the ashy chinchilla rat (Abrocoma cinerea). And without him, researchers would never have found Quebrada Maní.
The story begins like this. A chinchilla rat gathers up what little he can find in a desert—leaves, buds, seeds, and stems of shrubs—and carries it back to the nest he has built in a rocky crevice. There, he exercises one more key adaptation: he pees. He spreads his urine—which, to conserve water, is viscous and highly concentrated—all over that nest. Over time, the matrix ossifies into a crystalline structure harder than rock. The crystallized urine is known as “amberat”; the whole structure is called a midden.
Half a century ago, two North American researchers made a discovery. While hiking in Nevada’s Marble Mountains, they had the informed luck to crack open the midden of a desert packrat (Neotoma lepida). Peering into its innards, they found something amazing: the fossilized remains of trees and grasses that couldn’t possibly grow there today. Once, the midden revealed, this dry desert had supported lush woodlands.
Here was a scientific goldmine: by using radiocarbon dating, researchers could date the plant remains to determine what the landscape and climate were like thousands of years go. Rat middens were “a time capsule,” a window into the deserts’ past, says U.S. Geological Survey researcher Julio Betancourt, author of Packrat Middens: The Last 40,000 Years of Biotic Change and Latorre’s former PhD advisor. “Middens are the Rosetta Stone of reconstructing past vegetation,” Betancourt says.
Because the rats never scurried far from their nests, there was no doubt that their collections represented exactly which plants had been growing nearby.
“When you look at the plants packrats collected—which are pretty much leaves, seeds, and twigs from right near that spot—you know that it was collected by a packrat using packrat feet,” says Ken Cole, a research professor at Northern Arizona University who has used packrat middens to paint a picture of climate change in the Grand Canyon. “You can argue about how far the packrat may have gone, but the answer is: not very far.”
Today, Latorre has taken the method further. Researchers are learning that climate plays a crucial role in the rise and fall of civilizations—and nowhere is that more apparent than in the desert. So Latorre has been using chinchilla rat middens to create computerized elevation maps that show where the rain fell, and what plants grew where. For Latorre, crystallized pee has become a crystal ball: he uses it to predict which sites are most likely to have harbored humans.
For 16 years, Latorre has been scouring the desert to build his archive. This October, he tasted success for the first time. It was his midden map that predicted the location of Quebrada Maní, leading researchers to this remarkable find. And this year, he and his team have located new sites, some of them potentially even older. Still, Latorre dreams bigger. “Imagine,” he says, “something like Google Earth, that could show you all the middens on earth.”
Latorre has never seen a chinchilla rat in the flesh. But if he did, he’d like to give it a hug.