Host: Benjamin Thompson
Welcome back to the Nature Podcast. This week: reconstructing a 2-million-year-old ecosystem using environmental DNA, and modelling the climate emissions of the plastics sector. I’m Benjamin Thompson.
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Host: Benjamin Thompson
Last year on the podcast, we covered some research that saw scientists smash a long-standing record, by sequencing DNA recovered from mammoth teeth estimated to be over a million years old. But you know what they say about records, right? They’re there to be broken, and this week in Nature, a team reports sequencing DNA that’s even older. And what’s more, they’ve used it to recreate what an ecosystem in Northern Greenland might have been like 2 million years ago. Shamini Bundell takes up the story.
Interviewer: Shamini Bundell
For centuries, fossils have driven our understanding of ancient species, but fossilisation requires very specific conditions to preserve things like bone and, even then, palaeontologists often have to be lucky to find them. DNA, on the other hand, is everywhere.
Interviewer: Eske Willerslev
Every single cell in the body contains DNA. If I do like this, DNA will be on this table from me, right. So, we are walking around on DNA from the present and, if we dig down, DNA from the past.
Interviewer: Shamini Bundell
This is Eske Willerslev, a geneticist and palaeontologist at the University of Cambridge here in the UK, who helped pioneer a technique that uses ancient DNA to explore the past. Specifically, he and his colleagues look at what's known as environmental DNA or eDNA – that is DNA that's found in the environment rather than inside organisms. Eske has been looking for eDNA preserved in ancient soils.
Interviewer: Eske Willerslev
The DNA molecules are electrically charged, and some of the sediment particles in the soil are electrically charged, so DNA will bind to these sediment particles, and that will reduce the chemical degradation rate of the DNA.
Interviewer: Shamini Bundell
The colder it is, the better the DNA preservation. And so, one of the best places to look for any ancient DNA is in ground that's been continuously frozen, known as permafrost. So, in 2006, Eske and his colleagues headed high up into the Arctic Circle to Greenland in search of frozen ancient dirt and ancient DNA.
Interviewer: Eske Willerslev
It’s what we call an Arctic desert. I mean, it’s a stony area where you can just see life is really struggling to survive, and so are you when you’re up there, to be honest.
Interviewer: Shamini Bundell
The team took samples of permafrost from a barren hillside in what’s known as the Kap København Formation. The oldest of these samples dated back 2 million years. But when they tried looking for DNA back in 2006, they were out of luck.
Interviewer: Eske Willerslev
We tried, and we got nothing. And the general notion at that time was, well, DNA can maximum survive for 1 million years, so it wasn't that surprising. But every time we made improvements in our DNA extraction methods or our sequencing abilities, we went back and tried, and we failed, and we failed, and we failed, until a couple of years ago, and suddenly we got a hit.
Interviewer: Shamini Bundell
As the technology improved, the team were able to extract more and more short fragments of DNA bound to the sediment.
Interviewer: Eske Willerslev
So, at that stage, it was like, woah, we got DNA out that is 2 million years old. The second woah was, I think, when we got the animal DNA out because it was just incredible, right? I mean, we had so limited knowledge of what animals were there.
Interviewer: Shamini Bundell
At 2 million years old, this represents the oldest DNA yet sequenced. And by piecing together the DNA fragments, the team could work out which creatures were roaming the area all that time ago.
Interviewer: Eske Willerslev
And we could basically see this whole ecosystem come to life. There were mastodons running around, reindeers, geese, hares. Also, marine animals like the horseshoe crab, which suggested a much warmer environment, even in the sea, during that time, which was also surprising.
Interviewer: Shamini Bundell
The sequenced eDNA painted a picture of Greenland 2 million years ago that looked very different to what it does now. Mastodons, an ancient relative of elephants, were a particularly unexpected find.
Interviewer: Eske Willerslev
No one had predicted that mastodons should be around. It's found in North America. And Greenland, at that time, was also an island, so it was separated from North America, just as today, and therefore people didn't think that animals like mastodons could get there, right? So, either it must have been swimming from the Canadian islands into Greenland or potentially walked over the sea ice.
Interviewer: Shamini Bundell
Mastodon fossils have been found in various sites in North America, but never in Greenland, and according to Eske, this demonstrates some of the benefits of using eDNA to study ancient ecosystems, compared to studying fossils.
Interviewer: Eske Willerslev
Palaeontology, obviously, you can do more than just identify the bone. So, if you find parts of a skeleton, you can also say things about locomotion, for example. You can say something about whether it was damaged during life, for example. DNA can't tell you anything about that. But what DNA can is it gives you the opportunity to follow evolution in action, how species are genetically evolving and changing. It also gives an opportunity to not only see it on a species level, but a whole ecosystem level.
Interviewer: Shamini Bundell
The use of eDNA is growing among palaeontologists as techniques improve, and Eske is already thinking about how to extract even older DNA.
Interviewer: Eske Willerslev
I think it's definitely possible to go back further. We can see that some of the DNA that is captured in the sediments, we are not really able, at this stage, to properly release. When we become capable of doing that, and we're working on it, obviously, then I think you will target a whole new pool of DNA, and I think that will bring us significantly further back.
Interviewer: Shamini Bundell
The previous record for the oldest sequenced DNA was around half as old at 1.2 million years, and belonged to a mammoth frozen in Siberian permafrost. So, Eske’s 2-million-year-old DNA represents a significant step further back in time. But there may be a limit to the oldest DNA that can be recovered. Theoretically, the oldest permafrost that could still exist is 2.6 million years old because it was too warm for it to form prior to this. And of course, the study of DNA alone has its limitations. Without the fossil record, researchers wouldn't know much about these animals’ anatomy and life story. But when it comes to the more recent past, eDNA is an exciting new part of the palaeontologist’s toolkit.
Interviewer: Eske Willerslev
Conservation and ecology are using multiple tools and environmental DNA is becoming more and more a tool that people are using in order to describe communities, right. So, I think it will always be a combination of tools. And I'm sure also we will, in the future, see tools that I can't even imagine now, to be honest.
Interviewer: Shamini Bundell
But even now, there are many more ecosystems yet to be explored using environmental DNA, and perhaps many more surprises yet to be uncovered.
Interviewer: Eske Willerslev
I mean, this is why you do science, right? It's for those moments. It's just changing the way we look at things. And this is the dream of a scientist, right?
Host: Benjamin Thompson
The was Eske Willerslev from the University of Cambridge. Shamini has also made a video about this work, so look out for a link to that, and to the paper, in the show notes. Coming up, we’ll be hearing about new research that’s modelling the climate emissions of the plastics sector. Right now, though, it’s time for the Research Highlights, read this week by McKenzie Prillaman.
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McKenzie Prillaman
Low levels of ‘good’ cholesterol predict heart disease in white people in the United States. However, that link doesn’t hold for Black people. Past studies indicate that raised levels of high-density lipoprotein cholesterol, commonly called ‘good’ cholesterol, protect against heart disease. But these studies included mostly white participants. To study the impact of race on this link, a team collected blood samples and recorded heart disease among nearly 24,000 Black and white US adults for 10 years. Their analysis revealed that, in white participants, low levels of ‘good’ cholesterol were associated with increased risk of heart disease. They didn’t find that connection in Black participants. The researchers note that current heart-disease prediction models don’t account for racial differences in the effect of ‘good’ cholesterol levels. They suggest developing risk assessments that are independent of race to improve prevention and management of cardiovascular disease. Read that research in the Journal of the American College of Cardiology.
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McKenzie Prillaman
Humans might enjoy fireworks lighting up the sky, but Europe’s migratory geese sure don’t. Many people in western Europe celebrate New Year’s Eve with fireworks. To see how these loud, bright displays could disturb wild animals, researchers tracked the movement of about 350 geese of four different species in the weeks before and after the last night of the year. Eight years of tracking data suggest that geese near firework displays tend to fly farther from their roosting areas, and at higher altitudes, than they did on other nights. Geese also spent more time searching for food after being disturbed, possibly to make up for energy lost fleeing from fireworks. These findings suggest that the stress caused by fireworks can shape bird behaviour well into the new year. Flock to that research in Conservation Letters.
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Host: Benjamin Thompson
Next up on the show, reporter Alex Lathbridge has been diving into a new model which aims to investigate the role of plastics in the face of increasing emissions and climate change.
Interviewer: Alex Lathbridge
Plastics are one of the most versatile materials developed in the last century, but from landfills to microplastics in the oceans, more and more evidence highlights just how negative the impact that they have on health and the environment is. Now, one major impact they have is on the atmosphere, more specifically, greenhouse gases.
Interviewee: Paul Stegmann
Plastics are, right now, responsible for around 4.5% of global greenhouse gas emissions.
Interviewer: Alex Lathbridge
This is Paul Stegmann, a scientist and consultant on circular plastics modelling at TNO. He and his collaborators at Utrecht University in the Netherlands have been looking at the effects that the plastics sector have on greenhouse gases, more specifically, carbon dioxide, and using new modelling techniques to do so.
Interviewee: Paul Stegmann
In our work, we expected emissions would double until 2050. I think what is very important to know is that most of the carbon that is entering the plastic production is stored in the product, which means that many of the emissions of plastics appear after they are produced, at the end of life, for example. So, it's very important that we look at the entire lifecycle of plastics to understand the entire system impact of plastics over an entire lifecycle.
Interviewer: Alex Lathbridge
But with plastics being used so ubiquitously, where do you even start with simulating something so vast and complex?
Interviewee: Paul Stegmann
We looked at the very aggregate, abstract level on the plastics sector. So, we looked into historic data on which sectors plastics are used, how many are produced, what type of plastics are there. And based on this historic data, we then project different potential futures based on GDP per capita development, population development, different narratives of how our future could evolve, which is essentially how, in the climate modelling world, we try to explore potential futures and how they impact the climate.
Interviewer: Alex Lathbridge
Now, a key part of their work is that their model is integrated in a wider network of models. This is called integrated assessment modelling. Basically, it's trying to simulate the wider interactions of humans, the economy, the environment and the climate. So, for example, if land use in farming were to change, it would then have a knock-on effect on the plants and biomass that could be used for making plastics. Or if the costs payable by the companies that produce carbon emissions, sometimes known as the CO2 price, were to increase, this could change behaviour in many manufacturing sectors. So could a change in the energy sector and many other sectors. So, by linking their plastics model to other models from other sectors that simulate their own dynamics, they were better able to get a handle on the plastics sector and analyse a few potential solutions for the greenhouse gas emission problems and how they might play out in the future.
Interviewee: Paul Stegmann
For us, we have a baseline as kind of a business as usual, how the world would look if we don't change anything. And from there, we introduced a CO2 price which would be in line with our 2 °C target from the Paris climate agreement. And then we saw how this CO2 price alone was affecting the plastics sector, and also the other sectors that are linked to our sector. And in a second step, we then added a circular economy strategy to the model to see how we could reduce emissions if we recycle more, if we design our products differently, et cetera. And lastly, we looked at a certain circular bioeconomy scenario, I would call it, meaning that we have still the CO2 price in place, the circular economy strategies in place, and now we add more biomass use as feedstock to replace fossil fuels like coal and oil, and see how that plays out.
Interviewer: Alex Lathbridge
All of the potential futures that they modelled had benefits, but they also came with their own negatives, sometimes in the short term, and sometimes in the longer term. But one potential future looked promising to the team.
Interviewee: Paul Stegmann
Our circular bioeconomy scenario was kind of a combination of all of these measures. And this showed the best performance, in terms of reducing greenhouse gas emissions, even turning the plastics sector into a carbon sink by the end of the century. And also, at the same time, reducing the resource consumption of the plastics sector, and that we basically achieved by circular economy measures and by biomass use, and biomass use basically means that we also sequester CO2 from the air during the processing of plants that are then used to produce plastics. Then we use these plastics, keep them in the society by using them longer, repairing the products and eventually hopefully recycling them back into another use. In that way, we kind of create a temporary carbon storage that could have an important impact in reducing the emissions of the plastic sector.
Interviewer: Alex Lathbridge
Now, this model doesn't predict the future. It merely explores potential futures based on the best data given to it. But could a potential solution for greenhouse gas emissions also have a positive impact on the other problems caused by plastics?
Interviewee: Paul Stegmann
I see both co-benefits but also maybe some trade-offs with a circular bioeconomy strategy. By recycling plastics or having circular economy strategies in place, we also reduce flows from plastics into the environment. So, in that way, we also reduce plastic pollution and generation of microplastics. On the other side, if you use biomass for producing plastics, you also need land to produce biomass, and that, of course, could lead to other emissions in agriculture, talking about nitrogen emissions, for example, or maybe at freshwater bodies. So, that's why it's very important that we make sure that we have a sustainable biomass supply in the future, which does not impact other categories, like nitrogen emissions and water bodies that much.
Interviewer: Alex Lathbridge
This model, while large and very integrated, still focuses primarily on greenhouse gas emissions, and Paul says that more needs to be investigated to create sustainable long-term policies.
Interviewee: Paul Stegmann
We always have to keep the entire system and the different impacts in mind. I think people always oversee the limitations of one's work and while my work is useful for certain aspects, we cannot create our perfect policy out of my work. We need to consider other aspects. And I hope that people do that and read my article which is coming out very soon.
Host: Benjamin Thompson
Paul Stegmann there, from TNO, the Netherlands Organisation for Applied Scientific Research. For more on this work, look out for a link in the show notes. And that’s all for this week. But just before we go, a quick heads up to say that episode two of our podcast series Nature hits the books is now live. This time, writer and broadcaster Gaia Vince joined me to talk about her new book Nomad Century, which looks at how climate change could render large parts of the globe uninhabitable, and how surviving this catastrophe will require a planned migration of people on a scale never seen before in human history. Very interesting chat, that one, and look out for it wherever you get your podcasts. And don’t forget you can keep in touch with us on Twitter. We’re @NaturePodcast. Or you can send an email to podcast@nature.com. I’m Benjamin Thompson. See you next time.