Scientists define start of human impact on Earth's ecosystems

A team of international scientists is on the verge of officially declaring a new geological epoch, named the Anthropocene, characterised by the irreversible impact of human activity on Earth.

The Anthropocene Working Group (AWG) has selected Crawford Lake in Ontario, Canada, as the definitive starting point of this epoch.

The AWG, having studied 12 sites around the world, including an ice sheet in Antarctica, a peat bog in Poland and a coral reef in Australia, chose Crawford Lake due to its isolated nature.

The lake's isolation has allowed the gentle accumulation of sediment, capturing changes in the world above for 1,000 years.

Prof Francine McCarthy, a micropaleontologist at Brock University in Ontario and an AWG member, said: “Crawford Lake is completely isolated from the rest of the planet, except for what gently sinks to the bottom and accumulates as sediment.”

The term Anthropocene, meaning the human era, encapsulates the period in Earth's history when human activities began noticeably influencing global systems, from mountaintops to the ocean floor.

Scientists suggest this epoch began around the 1950s, marked by the appearance of human-made radioactive plutonium and the onset of “the great acceleration”, the dramatic surge of human activity across the globe.

Layers of mud beneath Crawford Lake have acted as a natural archive, preserving the signs of significant alterations in the planet's climate and chemistry caused by humans.

AWG secretary Dr Simon Turner, of University College London, said: “The sediments found at the bottom of Crawford Lake provide an exquisite record of recent environmental change over the last millennia.

“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.”

These markers are referred to by geologists as the “golden spike” or the Global Boundary Stratotype Section and Point, signifying the start of the Anthropocene epoch.

Samples from the lake, as well as other sites, have revealed traces of plutonium, a fallout of nuclear bombs tested in the atmosphere.

“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 Prof Andrew Cundy, an AWG member of the University of Southampton.

Other signs of human activity discovered in the samples were microplastics, coal-fired power station ash, concrete and high concentrations of heavy metals such as lead.

While some suggest the Anthropocene should start with the onset of the Industrial Revolution in Britain in the 18th century, AWG chairman and honorary professor at the University of Leicester, Colin Waters, said the effects of the revolution were not felt around the world at the same time.

He said consensus emerged around 2014 that the mid-20th century marked a globally synchronous change.

Currently, all Earth's inhabitants are officially considered to reside in the Holocene epoch, starting about 11,700 years ago when the climate became stable.

The Anthropocene, first coined by atmospheric chemist Paul Crutzen more than two decades ago, is still under discussion as a formal unit of geological time.

Prof Waters said the planet was unlikely to return to its Holocene state due to permanent human-induced changes resulting in greenhouse gas emissions, which could take millennia to return to Holocene levels.

The AWG scientists revealed their findings at the fourth International Congress on Stratigraphy in Lille, France.

As part of the next phase, the proposed Anthropocene epoch and Crawford Lake's status as its “golden spike” will have to pass through three more voting stages before official ratification.