Oldest DNA yet sequenced shows mastodons once roamed warmer Greenland

When once-living tissue is stored in a cold, dry environment, fragments of its DNA can survive for hundreds of thousands of years. In fact, the DNA doesn’t even have to remain in the tissue; we were able to get the DNA from the soil from previously inhabited environments. The DNA is damaged and broken into small fragments, but this is enough to allow DNA sequencing, which tells us about the species that once lived there.

In an amazing demonstration of how well this can work, researchers have obtained DNA from deposits that have been preserved in Greenland for approximately 2 million years. However, the deposits date back to a relatively warm period in Greenland’s past and reveal the presence of an entire ecosystem that once inhabited the country’s northern coast.

A different Greenland

Over the past million years or so, Earth’s glacial cycles have had relatively short warm periods that have not reached temperatures sufficient to remove the major ice sheets in the polar regions. But before that time, the cycles were shorter, the warm periods longer, and there were times when the ice sheets underwent major retreats. Estimates are that at that time minimum temperatures in northern Greenland were approximately 10°C higher than today.

During this period, a set of deposits called Cap Copenhagen was created in what is likely to be an estuarine environment. Some of the layers in this deposit are probably sediments washed into the area from a terrestrial environment, and other layers are sandy and were probably deposited by salt water.

Studies of these sites have turned up pollen from various plant species and a handful of animal fossils. They show that more species were present in this past ecosystem than are currently found in northern Greenland, but it is unclear how representative the findings are. Pollen can travel long distances, for example, and only a small fraction of animals are likely to be preserved.

So, a large international team decided to see if they could learn more about the ecosystem using environmental DNA. While Greenland remained warm for some time after these deposits, it was only relatively warm; winter lows were still well below freezing. And for hundreds of thousands of years, the area was generally as cold as you’d expect an area near the border between the Atlantic and Arctic Ocean to be.

The researchers then tried to figure out how old these deposits were. Based on a magnetic field reversal that occurred during the deposition of the Kap København Formation, they concluded that it was deposited either 1.9 or 2.1 million years ago—relatively close to previous estimates of 2.4 million years. They then factored that age and local climate into software that estimates the amount of damage the DNA must have accumulated. This suggests that there should be only a fraction of the damage that DNA would do in a warmer climate – the damage is likely reduced by more than 700 times.

The researchers say the minerals in the deposit interact with the DNA, pulling it out of solution and protecting it from any environmental enzymes.