In the middle of the South Atlantic, there's a patch of sea almost devoid of life. There are no birds, few fish, not even much plankton. But researchers report that they've found buried treasure under the empty waters: ancient DNA hidden in the muck of the sea floor, which lies 5000 meters below the waves.
The DNA, from tiny, one-celled sea creatures that lived up to 32,500 years ago, is the first to be recovered from the abyssal plains, the deep-sea bottoms that cover huge stretches of Earth. In a separate finding published this week, another research team reports teasing out plankton DNA that's up to 11,400 years old from the floor of the much shallower Black Sea. The researchers say that the ability to retrieve such old DNA from such large stretches of the planet's surface could help reveal everything from ancient climate to the evolutionary ecology of the seas.
"We have been able to show that the deep sea is the largest long-time archive of DNA, and a major window to study past biodiversity," says Pedro Martinez Arbizu, a deep-sea biologist of the German Centre for Marine Biodiversity Research in Wilhelmshaven.
The new studies are "very exciting," says micropaleontologist Bridget Wade of the University of Leeds in the United Kingdom, who was not connected to the research. Until now, it wasn't clear "how far back in time you could take these DNA studies. … These records are telling you new information that wasn't found in the fossil record."
The South Atlantic team went looking for DNA in plugs of silt and clay coaxed out of the ocean floor hundreds of kilometers off the Brazilian coast. The researchers were after genetic material from two related groups of marine organisms, the foraminifera and the radiolarians. Both are single-celled, and both include many species with beautiful pearly shells that fossilize nicely, making them a favorite target of researchers studying the prehistoric oceans.
The researchers used special pieces of DNA specific to radiolarians and foraminifera to fish out DNA from those groups. Then they sequenced the DNA and compared the results to known foraminifera and radiolarian DNA sequences. Their analysis showed they'd found 169 foraminifera species and 21 radiolarian species, many of which were unknown. What's more, many of the foraminifera species belonged to groups that don't form fossils