Paleontologists working in the Siberian tundra can trudge for kilometers without finding a bone from the mammoths or bison that once roamed the permafrost. But ancient DNA from these creatures and other ancient animal and plant life may be quite common underfoot, they say, preserved in sediments bearing no signs of fossils. If correct, the findings could free researchers “from the shackles of needing fossils to be able to look into the past," says Alan Cooper of the University of Oxford, U.K.
Ancient DNA is typically extracted from fossilized bones, tissue, or dung. But a team led by molecular biologists Eske Willerslev and Anders Hansen of the University of Copenhagen decided to look in the permafrost, a good haven for preserving DNA because it is constantly cold. The team started out looking for bacterial DNA, but to their surprise, they could recover fragments of chloroplast DNA in soil samples. The sediments yielded what the authors say is the oldest reliable ancient DNA so far, from plants up to 400,000 years old. They identified 28 families of angiosperms, gymnosperms, and mosses.
They also found DNA from eight animals, including modern denizens such as lemmings and extinct ones such as mammoths and steppe bison. Cooper's group matched the samples to those of known fossil bones, the collaborators report online in Science this week . The animal DNA was at most 30,000 years old, according to radiocarbon dating of the sediment. Perennially dry temperate caves in New Zealand, meanwhile, yielded ancient DNA from the extinct moa and a plant community much like that present before human colonization in A.D. 1000. "Importantly, this demonstrates that DNA can be preserved in soil for long periods, even in unfrozen conditions," Cooper says.
Much of the plant DNA probably derives from roots, which would have been well protected under ground; the animal DNA likely comes from cells excreted in urine and feces. "This technique truly will revolutionize our ability to reconstruct past flora and fauna," says paleoecologist Glen MacDonald of the University of California, Los Angeles.