Canadian lake's bomb signal may verify Earth's new epoch - the Anthropocene

To address these questions, the International Commission on Stratigraphy (ICS) created the Anthropocene Working Group. They have chosen Crawford Lake in Canada as the Global Boundary Stratotype Section and Point (GSSP) for the Anthropocene.

"The sediments found at the bottom of Crawford Lake provide an exquisite record of recent environmental change over the last millennia," said Dr. Simon Turner, secretary of the Anthropocene Working Group from UCL, in a press release. 

He explained that the yearly changes in water chemistry and ecology have created layers that can be studied to find various indicators of past human activity.

"It is this ability to precisely record and store this information as a geological archive that can be matched to historical global environmental changes which make sites such as Crawford Lake so important," he said.

The team gathered core sample sections from various environments worldwide, from coral reefs to ice sheets. Samples from these sites were then analyzed at the University of Southampton's GAU-Radioanalytical labs at the National Oceanography Centre in Southampton. 

Researchers there processed the samples to detect a key marker of human influence on the environment – the presence of plutonium. 

"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," said Professor Andrew Cundy, chair of 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," he added. 

He explained how the team saw decreased plutonium levels when the Nuclear Test-Ban Treaty was enacted in the mid-1960s.

Other geological signs of human activity include increased ash from coal power plants, higher amounts of heavy metals like lead, and the presence of plastic fibers and fragments. 

These align with 'The Great Acceleration,' a significant rise in various human activities like transportation and energy use, beginning in the mid-20th century and continuing to the present day.

While Crawford Lake and 12 secondary locations demonstrate high-resolution records of human influence, the ICS will decide next year whether to officially recognize the Anthropocene as a new geological time unit.