The floor of Crawford Lake in Ontario acts like a storybook, preserving Earth’s recent history in chronological order.
Crawford Lake reveals the activities of local Iroquoian communities from the late 13th to 15th centuries, all the way through to the present day.
This is because Crawford Lake is a meromictic lake, meaning that the dense bottom layer of water does not mix with the less dense upper layers.
“The isolated bottom layer of water remains under disturbed, enabling the accumulation of clearly laminated valves which record precise information about the time during which they were deposited,” according to the Anthropocene Working Group.
Experts have nominated Crawford Lake as representation for the start of the Anthropocene epoch, a proposed new geological era characterised by significant changes to the planet’s surface as a result of human behaviour. The Anthropocene is yet to be officially accepted as a unit of geologic time, but in 2016 a working group under the guidance of an International Commission on Stratigraphy subcommittee agreed that human behaviour has left scars so deep that they will remain evident even into the distant future.
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One of the most notable markers of the Anthropocene is the appearance of plutonium, a radioactive material that appeared in the mid-20th century as a result of hydrogen bomb tests.
“The presence of plutonium gives us a stark indicator of when humanity became such a dominant force that it could leave a unique global ‘fingerprint’ on our planet,” explained Professor Andrew Cundy, Chair in Environmental Radiochemistry at the University of Southampton and member of the Anthropocene Working Group.
“In nature, plutonium is only present in trace amounts. But in the early-1950s, when the first hydrogen bomb tests took place, we see an unprecedented increase and then spike in the levels of plutonium in core samples from around the world. We then see a decline in plutonium from the mid-1960s onwards when the Nuclear Test-Ban Treaty came into effect.”
Agreeing on a simple measure that defines the boundary between chapters in Earth’s history is just the first step. This measure requires agreement among scientists on a single location to define the boundaries.
Known as the Global Boundary Stratotype Section and Point, or a golden spike, plays a crucial role in standardising these borders between epochs. The Anthropocene Working Group has been evaluating potential golden spike sites, from Oued Akrech, Morocco, to Alano di Piave, Italy.
After spending three years assessing the qualities of a dozen potential golden spikes for the Anthropocene, finally the AGW has landed on Crawford Lake.
“Crawford Lake is so special because it allows us to see at annual resolution the changes in Earth history throughout two separate periods of human impact on this small lake,” micropalaeontologist Francine McCarthy of Brock University in Canada, a voting member of the AGW, said at a press briefing.
The lake’s unique properties, such as its small size, depth, and lack of water mixing create sediments that precisely record environmental changes over the past millennia.
To officially establish the Anthropocene in the International Chronostratigraphic Chart, the golden spike at Crawford Lake must undergo a series of voting by various commissions and unions. If successful, it will mark the moment when human activities permanently altered the planet.
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