Oldest DNA sequenced to date shows mastodons once roamed a warmer Greenland
When ever living tissue is kept in a cold, dry environment, fragments of DNA can survive for hundreds of thousands of years. In fact, DNA doesn’t even have to stay in tissue; we managed to get DNA from the ground of previously inhabited environments. The DNA is damaged and broken into small fragments, but it’s enough to enable DNA sequencing and tell us about the species that once lived there.
In an amazing demonstration of how well this can work, researchers obtained DNA from deposits preserved in Greenland for about 2 million years. However, the deposits date from a relatively warm period in Greenland’s past and reveal the presence of an entire ecosystem that once inhabited the country’s northern coast.
For the past million years or so, Earth’s ice cycles have had relatively brief warm spells that failed to reach sufficient temperatures to eliminate the large ice sheets in polar regions. But before then, the cycles were shorter, the warm spells longer, and there were times when the ice sheets underwent major retreats. It is estimated that around this time minimum temperatures in northern Greenland were about 10°C higher than today.
During this period, a series of deposits called the Kap København Formation was constructed in what would likely be an estuary environment. Some of the layers of this deposit are likely sediments washed into the area from a terrestrial environment, and other layers are sandy and likely saltwater deposited.
Studies of these deposits have found pollen from several plant species and a handful of animal fossils. These indicate that more species were present in this former ecosystem than are currently present in northern Greenland, but it is unclear how representative the finds are. For example, pollen can travel long distances and probably only a fraction of the animals will survive.
So a large international team decided to find out if they could learn more about the ecosystem using environmental DNA. Although 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 has generally been about as cold as you would expect in an area near the border between the Atlantic and the Arctic Ocean.
The researchers then tried to find out how old these deposits are. Based on a magnetic field reversal that occurred when the Kap København Formation was laid down, they concluded that it was deposited 1.9 or 2.1 million years ago — fairly close to previous estimates of 2.4 million years. They then plugged that age and local climate conditions into software that estimates the amount of damage the DNA should accumulate. This suggested that there would be only a small fraction of the damage DNA would have sustained in a warmer climate – the damage was probably more than 700 times smaller.
The researchers claim that the minerals in the deposit interact with DNA, pulling it out of solution and protecting it from environmental enzymes.
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