Scientists have reconstructed a 2 million year old ecosystem from ancient DNA: ScienceAlert

Scientists have made a significant breakthrough in reconstructing the history of our planet.

Greenland’s permafrost sedimentary deposits contained recoverable environmental DNA dating to around 2 million years ago. This is 1 million years older than the previous record – DNA of a woolly mammoth that roamed the Siberian tundra 1 million years ago.

This amazing work has allowed a team of scientists to reconstruct an ancient landscape, revealing a world far removed from the icy shores of the Arctic Circle.

“A new chapter spanning an additional 1 million years of history has finally been opened, and for the first time we can look directly at the DNA of an ecosystem that has passed this far back in time,” said geneticist Eske Willerslev from the University of Cambridge in the UK and the University of Copenhagen in Denmark.

“DNA can degrade quickly, but we’ve shown that under the right circumstances we can now go back further in time than anyone dared to imagine.”

Time is not kind to the remains of living beings; DNA will rapidly degrade due to environmental stresses (like hungry microbes), weather conditions, and geological processes. If ancient DNA is to survive, it usually does so locked away in teeth and bones, where it is relatively protected.

But the materials buried under the permafrost are also relatively protected.

Here, a range of samples taken from the ice and permafrost of the Kap København geological formation at the mouth of a fjord in northern Greenland have offered scientists the chance to recover and reconstruct the environmental DNA of distant times.

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Scientists obtained most of these samples years ago during other work; expeditions are expensive, so scientists often collect more than they need, just in case. These samples were in storage, waiting for the right project to come along.

“It was only when a new generation of DNA extraction and sequencing equipment was developed that we were able to locate and identify extremely small and damaged DNA fragments in sediment samples,” Explain geologist Kurt Kjær from the University of Copenhagen.

“It meant we could finally map a 2 million year old ecosystem.”

The DNA recovered from the samples after painstaking work would have been unusable just a few years ago: the fragments were tiny, a few nanometers long, very degraded and very incomplete.

However, advances in genetic sequencing over the past few decades have allowed scientists to build up a vast database of DNA from the world around us. These DNA libraries offered scientists a point of comparison for their complex DNA fragments.

These libraries meant that scientists could painstakingly piece together the missing pieces for a census of organisms whose genetic material had been locked away in rock for many millennia.

“The ancient DNA samples were found buried deep in sediments that had accumulated over 20,000 years,” Kjaer says. “The sediment was ultimately preserved in ice or permafrost and, crucially, was undisturbed by humans for 2 million years.”

This reconstruction revealed a variety of life forms compatible with a surprisingly temperate climate. Scientists have found animals related to reindeer and caribou, lemmings, geese, hares and, interestingly, mastodons.

Ants, fleas, corals and horseshoe crabs have also left their mark in the sediments, as have birches and poplars.

Of particular interest is the mastodon’s DNA, the researchers note. All other species have relatives that remain in Greenland today; previously, the mastodons were thought not to extend as far north as Greenland.

Other DNA samples – taken from microorganisms and fungi – are still being identified. A future article will describe the full extent of the ecosystem to the best of the scientists’ understanding.

However, some features are already emerging that suggest a much warmer climate in the region during the Lower Pleistocene – considerably warmer than current temperatures.

It alludes, say the researchers, to the future of the Earth in the face of climate change.

“One of the key factors here is how well species will be able to adapt to changing conditions resulting from a significant increase in temperature. The data suggests that more species can evolve and adapt at wildly variable temperatures than previously thought,” he added. said geogeneticist Mikkel Pederson from the University of Copenhagen.

“But, most importantly, these results show that they need time to do so. The speed of current global warming means organisms and species don’t have that time, so the climate emergency remains a huge threat. for biodiversity and the world – extinction is on the horizon for some species, including plants and trees.”

But for scientists, the work is a huge leap forward. Now that environmental DNA has been successfully extracted and interpreted from clay and quartz, it may be possible to do the same with ancient deposits elsewhere.

“If we can begin to explore the ancient DNA of clay grains from Africa, we may be able to gather groundbreaking information about the origin of many different species – perhaps even new insights into early humans and their ancestors,” Willerslev said. said.

“The possibilities are limitless.”

The research has been published in Nature.