Canadian lake sediments reveal start of Earth’s Anthropocene epoch – “Clearly, the biology of the planet has changed abruptly. We cannot go back to a Holocene state now.”

Correlation of significant shifts in or appearances of markers between sites documenting the onset of the Anthropocene. Collectively, the 12 reference sites, via analysis across many sites using similar multiple proxies, show the extent to which the proxies at each site cluster at an approximately coincident level around the mid-20th century, consistent with the Great Acceleration Event Array (GAEA) proposed by Waters et al. (2022). This demonstrates the degree to which the primary marker chosen at a site represents the range of critical changes encompassed by that section. Each site team has identified a level where significant changes cluster, these ranging in age between 1945 and 1968 CE, though for most sites the level chosen dates to the 1950s. Graphic: Waters, et al., 2023 / The Anthropocene Review — Correlation of significant shifts in or appearances of markers between sites documenting the onset of the Anthropocene. Collectively, the 12 reference sites, via analysis across many sites using similar multiple proxies, show the extent to which the proxies at each site cluster at an approximately coincident level around the mid-20th century, consistent with the Great Acceleration Event Array (GAEA) proposed by Waters et al. (2022). This demonstrates the degree to which the primary marker chosen at a site represents the range of critical changes encompassed by that section. Each site team has identified a level where significant changes cluster, these ranging in age between 1945 and 1968 CE, though for most sites the level chosen dates to the 1950s. Graphic: Waters, *et al*., 2023 / *The Anthropocene Review*

By David Stanway
11 July 2023

(Reuters) – Sediment deposited at Crawford Lake, a small but deep body of water in Canada’s Ontario province, provides unmistakable evidence that Earth entered a new human-driven geological chapter – the Anthropocene epoch – some seven decades ago, a team of scientists said on Tuesday.

The members of the Anthropocene Working Group (AWG) plan to submit the evidence to the international scientific body responsible for naming geological chapters in Earth’s history. The scientists conducted research at a dozen sites worldwide and cited Crawford Lake, near Toronto, as the location that provided particularly persuasive geological markers that the Anthropocene epoch – essentially the age of humans – has arrived.

Plutonium from nuclear weapons testing in the 1950s provided “a very clear marker” for the transition to the Anthropocene and was accompanied by a surge in fossil fuel and fertiliser consumption, profound changes in land use and a decline in biodiversity caused by farming, said AWG chair Colin Waters, a professor at the University of Leicester in Britain.

Presence of plutonium and other evidence was found in core samples of the Crawford Lake sediments.

“At present, we’ve had 70 years of the Anthropocene,” Waters said. “That has been long enough, because of the rapidity of the change and the preciseness of it, to recognise that we’ve moved into this new Earth state, and that it should be defined by a new geological epoch.”

11 July 2023: Sediment deposited at Crawford Lake in Canada’s Ontario province provides unmistakable evidence that Earth entered a new human-driven geological chapter, the Anthropocene epoch, some seven decades ago, a team of scientists said. Video: Reuters

The Anthropocene epoch is proposed as a chapter in Earth’s history reflecting the transformation of the planet’s climate and ecology as a result of human activity. But there has been disagreement within the scientific community about when this proposed epoch began and the evidence to demonstrate it.

The Anthropocene epoch has not yet been formally recognised by a scientific body called the International Commission on Stratigraphy. The Anthropocene, if it gains formal recognition, would follow the Holocene epoch, which began 11,700 years at the conclusion of the last Ice Age.

“Clearly the biology of the planet has changed abruptly,” Waters added. “We cannot go back to a Holocene state now.”

Layers of sediment deposited under bodies of water and other places can provide a record of changing environmental conditions over time. The scientists obtained core samples of sediment at Crawford Lake and sediments, soils, corals and ice samples at the other 11 sites.

The sediment at Crawford Lake, the scientists said, showed a “golden spike” illustrating a sudden – in geological terms – and irreversible shift in Earth’s conditions. Such golden spikes – formally ending one geological chapter and ushering in another – would be observable in rock, glaciers or marine sediments for thousands of years to come.

“The record at Crawford Lake is representative of the changes that make the time since the mid-20th century geologically different from before, and worthy – we think – of the golden spike,” said Francine McCarthy, an AWG member and professor of earth sciences at Brock University in Canada.

Crawford Lake sediments provided a record of accelerating changes that have unfolded in the past few decades, including traces of fly ash produced by burning fossil fuels. Shifts in the composition of the sediments also reflected a wide range of other human impacts including acid rain, global warming and biodiversity loss, the scientists said.

An aerial view of Crawford Lake as a team consisting of scientists from Carleton University and Brock University gather sediment layer samples from the lake bottom at the Crawford Lake Conservation Area near Milton, Ontario, Canada, 12 April 2023. The view under the surface of Crawford Lake tells a different story. Scientists believe the lake's exceptionally well-preserved sediment layers serve as a reference point for a proposed new geological chapter in the planet's history, defined by the considerable changes wrought by human activity: the Anthropocene. The International Commission on Stratigraphy's Anthropocene Working Group on 11 July 2023, named the lake as the embodiment of the proposed Anthropocene epoch. Photo: Peter POWER / AFP — An aerial view of Crawford Lake as a team consisting of scientists from Carleton University and Brock University gather sediment layer samples from the lake bottom at the Crawford Lake Conservation Area near Milton, Ontario, Canada, 12 April 2023. The view under the surface of Crawford Lake tells a different story. Scientists believe the lake’s exceptionally well-preserved sediment layers serve as a reference point for a proposed new geological chapter in the planet’s history, defined by the considerable changes wrought by human activity: the Anthropocene. The International Commission on Stratigraphy’s Anthropocene Working Group on 11 July 2023, named the lake as the embodiment of the proposed Anthropocene epoch. Photo: Peter POWER / AFP

The precise time when the proposed epoch started remains contentious. Some suggest it began at the time of the Industrial Revolution of the 18th and 19th centuries or earlier. The AWG team said the more profound changes did not take place until the 1950s, when rapid economic and population growth drove up greenhouse gas emissions, and when radionuclides from weapons testing also infiltrated soils and sediments, coral, tree rings and glaciers.

“These radionuclides, particularly plutonium, effectively fingerprint the early 1950s in geological materials worldwide – in ultra-trace amounts – providing a radioactive marker that will persist for over 100,000 years,” said AWG member Andrew Cundy, a professor of environmental radioactivity at the University of Southampton in Britain.

The debate continues.

“I’m a little bit cynical about the exercise because it is like trying to pin an exact date on a process that has been playing out over a period of more than 50,000 years, probably more than 100,000, as humans have expanded across the planet,” said Bill Laurance, a biologist at James Cook University in Australia.

Canadian lake sediments reveal start of Earth’s Anthropocene age, scientists say

Map showing the location of the 12 candidate and other reference localities used for determining the global boundary stratotype section and point of the Anthropocene series, indicating the depositional environment. Satellite image: NASA visible earth. Reproduced from Head et al., 2022. Graphic: Waters, et al., 2023 / The Anthropocene Review — Map showing the location of the 12 candidate and other reference localities used for determining the global boundary stratotype section and point of the Anthropocene series, indicating the depositional environment. Satellite image: NASA visible earth. Reproduced from Head, *et al*., 2022. Graphic: Waters, *et al*., 2023 / *The Anthropocene Review*

Candidate sites and other reference sections for the Global boundary Stratotype Section and Point of the Anthropocene series

ABSTRACT: We review and compare proposals for 12 reference sections submitted to the Anthropocene Working Group of the International Subcommission on Quaternary Stratigraphy, of which one will be recommended as the Global boundary Stratotype Section and Point (GSSP) to define the base of the Anthropocene as a series within the Geological Time Scale. The sites span five continents and are located in diverse environments, with all but one sampled by coring. Many sites show annually resolved laminae (here considered optimal for GSSP selection) that can be independently dated radiometrically to confirm a complete succession over the critical interval. An extensive range of proxies, documenting profound human modification of the Earth System at around the mid-20th century interval, has been analysed. Airborne signals (e.g. radioisotopes, fly ash, stable carbon and nitrogen isotopes) provide the most widespread and near-isochronous proxies, applicable across most environments. Additional means of correlation include the appearance of microplastics and persistent organic pollutants, and shifts in heavy metal concentrations and lead isotope ratios. Assemblage changes of microfossils (and some macrofossils) in marine, estuarine and lake settings reflect environmental changes and biological introductions. These systematic and comprehensive datasets, with correlation established between sections, provide the basis for a proposal to formalize the Anthropocene.

Candidate sites and other reference sections for the Global boundary Stratotype Section and Point of the Anthropocene series