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Irish Examiner

Michelle McKeown: Crawford Lake and the marking of human impact on nature

Nestled in the heart of southern Ontario, Canada, Crawford Lake is a tranquil body of water with an extraordinary secret: it preserves history with uncanny precision. Its deep, undisturbed waters have acted like a natural time capsule, trapping layers of sediment year after year, each recording a snapshot of the environment at the time of deposition. Because of this, Crawford Lake became a star candidate in a global scientific quest: to identify the Golden Spike – a single, globally synchronous signal in Earth's geological record that would define the start of a new epoch, the Anthropocene. Age of humans The Anthropocene, meaning 'the age of humans,' is the proposed name for a new geological epoch to mark the profound and accelerating influence of humans on the Earth's systems. For decades, scientists have debated whether our species' impact, through greenhouse gas emissions, industrial agriculture, nuclear testing, plastic pollution, and accelerated biodiversity loss, has been so significant that it warrants a formal entry into the geologic timescale. The current epoch, the Holocene, began approximately 11,700 years ago following the last Ice Age. It marks a period of relative climate stability during which human civilisations flourished. But the 20th century, particularly the post-World War II era known as the Great Acceleration, saw an unprecedented surge in human activity, industrialisation, population, and consumption, leaving an imprint on the planet. These include rising carbon dioxide levels, radioactive isotopes from nuclear tests, and microplastic deposits. These changes are now preserved in sediments, ice cores, and even coral reefs. To formally define the Anthropocene, geologists needed more than just evidence of human impact. They needed a precise Global Boundary Stratotype Section and Point (GSSP), which is a physical reference point in the geological record that could be used to demarcate the boundary between epochs. This is where Crawford Lake came in. Crawford Lake What made Crawford Lake such a strong contender was its unique ability to record annual layers of sediment (known as varves) with exceptional clarity. These fine layers act like tree rings, preserving an exact year-by-year account of environmental change. Sediment cores taken from the lake bed revealed tell-tale signs of the Anthropocene's onset, including plutonium isotopes from nuclear bomb testing in the early 1950s, along with spikes in fly ash, heavy metals, and chemical pollutants. In 2023, the Anthropocene Working Group (AWG), which is an international body of scientists studying the issue, voted in favour of using Crawford Lake as the site to define the start of the new epoch. But in a twist worthy of geological drama, the proposal was rejected. What happened? In March 2024, the Subcommission on Quaternary Stratigraphy (the official scientific body tasked with approving changes to the geologic timescale), which advises the International Union of Geological Sciences (IUGS), voted against formalising the Anthropocene as a new epoch. This decision halted the formalisation of the Anthropocene as a new epoch and left Crawford Lake without the golden spike claim. Why the rejection? At the heart of the issue is a fundamental debate about what geology should, and should not, do. Critics of the Anthropocene designation argued that the concept is more cultural than geological, better suited to environmental studies, history, or political discourse than to a rigid geological framework. They questioned whether the changes observed in the mid-20th century are truly global, continuous, and long-lasting enough to warrant a formal stratigraphic boundary. After all, many of the markers, such as plastics and radionuclides, are relatively new, and their long-term persistence in the geological record remains uncertain. Others expressed concern that the proposal was too narrow, focused excessively on recent decades without sufficient regard for earlier human impacts on the planet. For example, large-scale deforestation, species extinctions, and agricultural transformations have been reshaping the Earth for thousands of years. So why draw the line in the 1950s? Is the Anthropocene real? But rejection of the proposal doesn't mean the Anthropocene isn't real. In fact, most scientists agree that human activity has pushed the Earth into a new state, marked by climate breakdown, biodiversity collapse, and novel materials like concrete and plastics. What's in dispute is not whether we've altered the planet, but how best to categorise that change. Crawford Lake, meanwhile, remains a place of global importance. It tells the story not just of atomic fallout and pollution, but of indigenous communities who lived around its shores centuries ago, leaving behind traces of corn and wood ash in its sediments. It is both a natural archive and a cultural mirror, reflecting the deep entanglement of humans and nature. A story still worth telling Perhaps the Anthropocene doesn't need a formal boundary, or a single lake, to change how we see our place in the world. While Crawford Lake offered a strikingly clear and symbolic record of recent human impact, no single site can fully capture the complexity or timeline of our planetary influence. What matters more is the broader shift in awareness the debate has sparked. The true legacy of the Anthropocene may lie not in a line drawn in the mud, but in how it urges us to confront the scale of our actions, and to choose, with urgency and humility, what kind of future we want to leave behind. Read More Michelle McKeown: Shedding light on the wild world of bioluminescence