When tissue is once preserved alive in a cold, dry environment, fragments of its DNA can survive for hundreds of thousands of years. In fact, DNA should not even remain in the tissue; We were able to obtain DNA from previously inhabited soil environments. The DNA is damaged and broken into small pieces, but it is enough to allow the DNA sequence to tell us about the species that once lived there.
In an amazing demonstration of how well it can work, researchers have obtained DNA from deposits in Greenland preserved for about 2 million years. However, the deposits date from a relatively warm period in the past in Greenland and show the presence of an entire ecosystem that once inhabited the northern coast of the country.
During the last million years or so, the Earth’s glacial cycles have had relatively warm periods, with temperatures not high enough to remove the major ice sheets in the polar regions. But before this time, the cycles were shorter, the warm periods longer, and the ice sheets underwent periods of major retreat. Estimates are that around this time the minimum temperatures in northern Greenland were about 10° C higher than they are now.
At this time, a deposit system called Kap København was placed in what was to become an estuary. Some of this layer of deposit is likely to be sediments that were washed down from the ground in the area, and others are sandy layers and probably deposited by salt water.
Studies of these deposits have found pollen from various plant species and a few animal fossils. These indicate that more species were found in this ecosystem in the past than are now found in northern Greenland, but it is unclear how representative they were found. Pollen can travel long distances, for example, and only a fraction of the animals are usually preserved.
So, a large international company decided to explore whether they could learn more about the surrounding ecosystem using DNA. While Greenland was warmed for some time after these deposits, the soil was relatively warm; winter still roars even below the torpor. But for 100,000 years the area was about as cold as you would expect an area near the border of the Atlantic and Arctic oceans to be.
The researchers then tried to look at how these ancient deposits were deposited. Based on the magnetic field reversal that took place to place the Kap København Formation, they concluded that it was placed either 1.9 or 2.1 million years ago—right close to past estimates of 2.4 million years. That age and local climate conditions are then plugged into software that estimates the amount of DNA damage that should accumulate. This suggested that the DNA was only a fraction of the damage in a warmer climate – the damage is likely to have dropped more than 700 percent.
The researchers argue that the minerals in the deposit interact with the DNA, extracting it from the solution and protecting it from all environmental enzymes.
#oldest #DNA #sequences #show #mastodons #roamed #warmer #Greenland