Over the past 450,000 years, Earth has undergone five ice age cycles from cold to warm climatic periods and back again. Each transition has had a major impact on plant and animal habitats. We are now facing a warming climate, which will cause major changes to the biosphere.

“We have a fairly good understanding of the impact that the warming at the end of the last ice age had on global ecosystems. But it’s quite possible that the ends of earlier ice ages impacted plants and animals in a completely different way,” says Heintzman, who has a PhD in paleogenetics from the University of London and is leading a research team at Stockholm University.

Heintzman is traveling several hundred thousand years back in time with the help of sediment samples and advanced genetics. His research field is paleogenetics, which marries paleontology and archaeology with modern biomolecular and genetic methods.

“We’re taking advantage of recent rapid technical developments in DNA analysis, and are using new methods to examine sediment samples. This gives us snapshots of how ecosystems looked several hundred thousand years ago,” he says.

Simply put, all DNA from a soil sample is sifted out to identify the plant and animal material it contains. This provides an overview of the ecosystem at a given point in history – the animals that were living there, and the trees and shrubs growing at the time.

Oldest ever DNA

It was only three years ago that the oldest DNA ever obtained was extracted from a horse that lived 700,000 years ago. That record has now been crushed. In a recently published paper, researchers at Stockholm University, including Heintzman, revealed they had obtained DNA from a mammoth that roamed the steppes of Siberia some 1.2 million years ago.

“When we go so far back in time, it’s also possible to follow close on the heels of evolution. We track changes in DNA to see how animals and plants evolved up to the present day – how different ecosystems change and how some are also lost,” Heintzman explains.

The Centre for Palaeogenetics is one of the few places in the world where it is possible to extract and analyze prehistoric DNA on this scale.

This knowledge can help us understand the difficulties we face – which species may require extra help to survive impending climate change.

“When we know the way and the rate at which ecosystems change, we’ll also be better able to predict our future. We can see it took a millennium for an ecosystem resembling the current one to develop after the last ice age in northern Scandinavia. This knowledge gives us an idea of the time it takes for an ecosystem to recover from climate change.”

Making use of earlier research

The sediment is obtained in the form of core samples from land and sea. Marine samples are already available from previous research at Stockholm University, mainly from the bottom of the Arctic Ocean. To obtain terrestrial samples, Heintzman and his colleagues visited several sites in Alaska and northern Canada last summer. Those sites are in areas that have been ice-free for the past million years, making them particularly suitable for sampling.

In the basement at the Department of Geological Sciences, the cores are divided up so they can be sampled and dated. The traditional carbon-14 method does not suffice for this purpose, since it only works on samples up to about 50,000 years old. Other methods are needed. One approach the researchers are using is to examine ash from prehistoric volcanic eruptions. Each eruption leaves its own geological fingerprints, which can be analyzed and dated.

Once they have been dated, the samples are searched for DNA from plants and animals. Multiple methods – collectively known as metagenomics – are used to isolate and identify DNA. The aim is to find as much DNA as possible, while eliminating bacteria and fungi that may be of more recent origin.

All DNA found is then sequenced and compared with open genomic databases such as those generated by the Earth Biogenome Project. This is a global initiative whose goal is to map the DNA of over a million species. Sweden is contributing knowledge and expertise from SciLifeLab to this effort.

“None of what we’re doing is easy – we’re working rather like detectives do. But with the help of modern genetic methods, we can fill in the pieces of a jigsaw puzzle showing the plants and animals that create whole ecosystems. We have a very good chance of filling in many of the gaps in our current knowledge,” Heintzman says.

Several of the methods being used were developed by Heintzman at the Arctic University of Norway and University of California Santa Cruz. He is currently researching at the Centre for Palaeogenetics at Stockholm University.

Even as a child he was interested in prehistory. He grew up in rural England, and used to try to imagine how the landscape would have looked and how people lived when all of England was forested.

“Perhaps I could have been a paleontologist, but when I did my master’s I read up on ancient DNA. It was a field that allowed me to combine my interests in the past natural world with biology and chemistry. I’ve had no regrets since,” says Heintzman.

Text Magnus Trogen Pahlén
Translation Maxwell Arding
Photo Magnus Bergström