– This will be a huge step forward. It is a significant event that, when the time comes, we can say that we are in a new era. An era that we – as a species – have brought about, associate professor Henrik Hovland Svensen of the University of Oslo tells Dagbladet.
Plutonium tailings from nuclear testing and fly ash from coal-fired power plants are basically not something you want in your local lake.
But it’s the findings of these phenomena – along with other clear signs of the effects of industrial pollution, rising temperatures and loss of species diversity – that make Canada’s Crawford Lake, Milton, in Ontario, is making headlines around the world.
A group of researchers believe the lake proves a 23-year-old hypothesis that has divided experts for several years:
That humanity has left geological traces on the globe to such an extent that we can no longer say that we are in the geological era Holocene – which, according to the current geological chronology, began 1170 years ago – but at the “age of man”, the Anthropocene.
– Very promising
Since 2009, researchers from the Anthropocene Working Group (AWG) have been working to determine whether the Anthropocene – which they say began in 1950 – meets the criteria to be classified as a distinct geological epoch.
They now believe the answer is yes – and geologist Svensen is optimistic in their favour.
– The reason why it is very promising is that the Canadian lake is of a particular type – which we also have in Norway, he says – and at the same time reminds that the work has not yet been peer reviewed nor published.
Crawford Lake is what is called meromictic lakeexplains Svensen.
– There are lakes where there is no circulation in spring and autumn, so the bottom water is completely calm. Metals and salts then accumulate – and the bottom water is low in oxygen. When the silt then settles to the bottom of the lake, it settles in very neat layers called varves.
A lack of oxygen in bottom waters also prevents bottom organisms from “rooting” the bottom mud, he explains.
This combination of properties causes layers of mud to settle on the seabed like the annual rings of a tree trunk.
– If you drop a pipe in the bottom and then it rises, you can see these layers. A light layer and a dark layer correspond to one year, depending on the lake. Then you can just count down in time, he says.
That’s what the AWG researchers did, according to Svensen.
– They counted the time, then they measured the plutonium content of the atomic bombs – and many other things – in each layer. They will then be able to find out exactly which year the plutonium can be attributed to.
The plutonium present in these layers is uniquely suited as a feature of the Anthropocene, as nuclear testing caused the radioactive element to circulate across the globe via the atmosphere.
– When it then spreads all over the world, it marks a global change. The spread of plutonium via the atmosphere occurred simultaneously all over the world.
– Mass extinction
The concept the Anthropocenein its modern sense, was popularized by Dutch chemist Paul Josef Crutzen in 2000.
But what if we live in the Anthropocene Or Holocene?
– What geologists do is compare the Anthropocene to the rapid climate changes and mass extinctions that have taken place on Earth in the past, Svensen explains.
To find geological changes of the same magnitude as those that occurred during the Anthropocene – that is to say since 1950 – you have to go back millions of years, insists the geologist.
A frequently used comparison, according to Svensen, is Permian-Triassic extinction – the largest mass extinction in the history of the planet – 252 million years ago.
During this period, more than 95 percent of marine species and 70 percent of terrestrial species died, according to British Encyclopedia.
– The Anthropocene is at that level – almost. Formally speaking, we are not there yet. But we have to compare the dramatic changes we observed earlier in geological history.
– No one knows where it ends
75 years is not much in a geological context, underlines Svensen.
But the geological changes that have occurred in such a short time can reach the same order of magnitude as those that occurred millions of years ago, he says.
The debate over the Anthropocene occurs in almost every existing academic discipline, according to the geologist.
– It’s about nature, people and the human footprint. It is above all about politics. It comes in on land use planning, concerns about climate change – and our relationship to the possible ‘sixth mass extinction’.
The term “sixth mass extinction” is used by some to refer to the rapid, human-induced loss of biological diversity – and by others for a scenario where it gets even worse in the future, according to Great Norwegian Encyclopedia.
– And no one knows where the Anthropocene will end – in terms of a possible mass extinction, says Svensen.
Knowledge of the Anthropocene will also enter reports that form part of the decision-making basis for major international policy decisions – such as UN climate reports, he believes.
– A lot has changed just by introducing the word Anthropocene 23 years ago. This has sparked long debates and makes us see the Earth in a completely new way. The fact that it can be documented, geologically and geochemically, is absolutely essential.
The golden nail
But to declare a geological epoch, experts need a “golden nail”.
A golden nail – or a “World Boundary Stratotype Section and Points”as it is called in technical language, is an internationally recognized reference point that defines the starting point of a stage on the scale of geological time.
In this case: A physical place that marks the passage from one era to another.
– A golden nail is a point of reference – in a way type locality – with which all other localities can be compared. This somehow becomes the norm for the period concerned.
When the International Commission on Stratigraphy has approved such a reference point, it is marked by driving a golden nail (hence its name) into the ground, rock face or wherever the point is.
That’s what AWG researchers believe they discovered at Crawford Lake.
But they could just as well be targeting Norway, Svensen believes, for example on the Sagtjernet in Elverum or other meromictic lakes, where Norwegian researchers are studying the lake bed.
“I’d like to think that might be a good candidate,” he said.
However, this would require different methods than those used by Norwegian researchers researching at Sagtjernet.
– The bottom of the lake is very soft and the first few centimeters contain a lot of water. It’s easy to mess up diapers when you pick them up. We then cannot study the last 20 to 30 years, he says.
The AWG researchers used a special method where sediment and water are frozen – so they can be retrieved without being ‘spoiled’.
– There are very few such studies in Norway and we tend to focus on periods further back than the Anthropocene. But they probably could have found a golden nail here, because we have a number of meromictic lakes in Norway.
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