Canada’s Crawford Lake Identified as Site for Marking New Geological Period

By Sharon Atieno

Scientists have identified Crawford Lake in Canada as the most appropriate location to find evidence marking the new geological period in the earth’s history.

The new period, which scientists have labeled, the Anthropocene epoch, refers to a period where human activities have contributed significantly to changes occurring on earth including global warming.

The announcement was made by the Anthropocene Working Group (AWG) during the 4th International Congress on Statigraphy in Lille, France.

The Lake was chosen from a list of 12 sites that had been proposed by scientists to provide evidence of this new period. They include San Francisco Bay (USA), Ernesto Cave (Italy), Karlsplatz (Vienna), SE-Dome ice core (Greenland), Xiamen Bay (China), Sniezka Peatland (Poland), East Gotland Basin (Baltic Sea), Sihailongwan (China) and Beppu Bay (Japan) among others.

The evidence gathered from Lake Crawford will contribute to the official declaration of this new geological period.

Speaking during said during a media briefing held by the Science Media Centre Germany, Prof. Francine McCarthy, geologist, Brook University in Canada and AWG member, the sinkhole Lake was ideal to be a Global Boundary Stratotype Sections and Points (GSSP) point because of its nature and structure.

The Lake has a depth of nearly 24 metres, a small size of 2.4 hectares and a shape that restricts the mixing of the water column so that the bottom waters do not mix with the surface waters.

“The bottom of the lake is completely isolated from the rest of the planet, except for what gently sinks to the bottom and accumulates in sediment,” she said.

“Within the annually laminated sediments, there are a number of markers, what we call
proxies, that are retained in the geologic record that will be retained there for many, many years to come. That people can come back to and at annual resolution, identify what was going on or reconstruct what was going on in the atmosphere.”

Additionally, Prof. McCarthy noted that the patterns formed by calcite sediments in the Lake are very distinct like fingerprints hence the scientists will be able to count each layer and identify exactly which year the changes started taking place.

Tasked with the mandate of defining the Anthropocene Earth Age, the AWG in 2016 decided that the Anthropocene period should be defined from the mid-20th century onwards when the Great Acceleration started taking place.

The  Great Acceleration refers to the dramatic increase in human activity and its impact on the earth system such as increased carbon dioxide emissions, ocean acidification, habitat destruction, extinction and widescale natural resource extraction among others.

The most significant marker to be used by scientists to provide evidence of this new timeline is plutonium, a radioactive chemical element used to make the atomic bomb in the 1950s.

“Because of the aboveground nuclear detonations, the testing that went on in the 1950s, there’s a very precise geochemical boundary that is present across the planet, across all environments,” noted Prof. Colin Waters Honorary Professor at the School of Geography, Geology and the Environment, University of Leicester, UK and AWG Chair.

“The presence of the plutonium mark is a very useful tool to allow you to define that boundary. And of course, since the 1960s, that signal has in effect been reduced because of the limited test ban treaty. There are no longer these above-ground destinations, so there’s no more plutonium being added to the atmosphere.”

Epochs can last for millions of years and are characterized by significant changes in rock layers, such as mineral composition and the appearance of distinctive fossils. Each variation reflects a major climatic change.

For the last 11,500 years, the earth has been in the Holocene epoch which began at the end of the last ice age- a period when glaciers that had previously covered the earth disappeared. This period was defined by the rapid population growth of species and the development of modern civilizations.

Being that the ability to detect the activity of radionuclide decreases through time with decay, secondary markers will also be examined by the Crawford team. These include spheroidal carbonaceous particles or fly ash (produced by very high-temperature combustion of fossil fuels, primarily coal, and primarily in industrial applications like steel mills) and nitrogen isotopes (produced from the production of nitrogen fertilizers).

Following the research findings, the scientists will submit their final submissions to the Subcommission on Quaternary Stratigraphy (SQS), AWG’s parent body. The submission will include a detailed justification of why the Anthropocene should be added to the international chronostratigraphic chart as a formal geological time unit at epoch rank and the Crawfordian at age rank.

It will also provide a full description of the proposed Crawford GSSP site as this needs a final vote to confirm the precise level of the GSSP in the core. This is because the team had proposed 1950 coinciding with a distinct level core and linked to the Great Acceleration concept. However, previous discussions in the AWG had expressed a preference to linking the base of the Anthropocene to the abrupt increase in plutonium in the core.

“Existing data couldn’t provide the date of this upturn to annual resolution. So, the Crawford team is currently carrying out additional plutonium analysis to ensure annual resolution so the decision can be made,” explained Prof. Waters.

With a new regulation allowing for the selection of other sites which meet the criteria of the GSSP to support its research, the AWG members are currently voting to choose which of the eight remaining sites should be selected and added to the proposal.

According to Prof. Waters, once the proposal is received by SQS they will need to discuss the content, then vote on the three parts covered by the report.  The report will be ratified if it passes the 60% threshold vote at the International Commission on Stratigraphy (ICS) and the International Union of Geological Sciences (IUGS) levels respectively.

This process is expected to be completed in time for the International Geological Congress in Busan, Korea, in August 2024.

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