Long after we are gone, a remote Canadian lake will show how we set about destroying Earth as a habitat

Scientists trying to date the start of the Anthropocene epoch have found in Lake Crawford’s sediment an exquisite record of environmental change over millennia
It’s an important reminder that humans are now a ‘geological superpower’ in the process of changing our planet forever – and not for the better

David Dodwell

Published: 4:45pm, 14 Jul 2023

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Imagine aliens landing on earth 500,000 years from now. By then, humans are likely to be long gone, exterminated by the global warming triggered by our orgy of carbon dioxide generation, environmental destruction and pollution.

This week in Lille in France, the obscure International Commission on Stratigraphy has been holding its fourth congress, focused on work of immense value to visiting aliens: will there be anything in the geological record that shows we were here? If so, what will be the “golden spike” that sets a time and date to when humans set about destroying the balmy equilibrium that, for 11,700 years of the Holocene epoch, enabled Homo sapiens to thrive and distinctively shape the world?

All this revolves around the heated debate among geologists and climatologists about whether humans have had so powerful an impact on Earth that we have tipped us out of the Holocene into the Anthropocene epoch, coined by chemistry Nobel laureate Paul Crutzen two decades ago.

At the heart of the Lille congress, a small but highly influential group called the Anthropocene Working Group reported on these two huge geological questions. Their conclusions? Yes, we have left markers across the globe that are likely to still be clear 500,000 years later; and the date we flipped from Holocene to Anthropocene should be set in the early 1950s.

After examining a shortlist of 12 locations across the world that can provide the clearest markers of this flip, and identify the impact that humans had on Earth, they agreed to focus on Lake Crawford, a tiny, remote lake around 60km west of Toronto in Canada.

Lake Crawford is special because sediments at the bottom of the lake provide an exquisite record of environmental change over millennia, allowing us to see year-by-year changes in Earth’s geological history.

Scientists say the lake has extraordinary characteristics. Being small and deep, the lake’s waters don’t mix easily. Calcium and carbonate from nearby rocks dissolve in its waters and combine in warm weather to form crystals that settle on the floor, defining every season, deep into human history.

Core samples show a change around 1950 as the geological impact of human activity became sharply more pervasive: this marks the start of the Anthropocene – the human epoch.

Of course, the first evidence of homo sapiens dates back at least 315,000 years to Morocco, with fire and hunter-gatherer activities recorded around 170,000 years ago. But these human communities came and went without disturbing the global ecosystem very much. It was only around 1950 that we saw the “great acceleration” in which an array of human activity had such a significant global impact that the relative stability of the Holocene epoch was pushed horribly out of equilibrium. This is about carbon dioxide emissions and global warming, but also a great deal more: changes that will for millennia leave indelible geological footprints.

The first clear and pervasive marker of the Anthropocene was a thin but distinctive layer of plutonium, laid down by the hydrogen bomb testing that started late in 1952 in Enewetak Atoll of the Marshall Islands in the Pacific. It continued for over a decade until the 1963 worldwide ban on nuclear testing. This created a unique, time-specific, global marker that will remain clear for millennia.

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At the same time, the global surge in fly ash produced by coal-fired power stations provided another distinctive marker dated very precisely to the early 1950s.

Then came plastics and microplastics, heavy metals, industrial chemicals and concrete. From this date forward, geologists have begun to find colourful stones fused with plastic and new minerals like Simonkolleite (weathered zinc slag) that are the result of pollution and human activity.

Geologists warn of other distinctive markers that will define our human impact. A British Geological Survey team has calculated that building activity, whether for towns and cities or for roads and railways, moves 24 times more material around the surface of the environment than all the material moved by the world’s rivers into the sea.

As a result, humans create around 316 billion tonnes of sediment annually (which amounts to a massive cube of 150km by 150km, if you can imagine such a thing). Erosion and uplift in the “far future” will expose these “currently unseen activities”. It will also probably confound any visiting alien geologists.

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The human population explosion, and our insatiable lust for consumption, has created landfills worldwide that are likely to stand the test of geological time, compressed and compounded like those prehistoric forests that were buried and eventually transformed into coal, oil and natural gas.

Another distinctive marker is likely to be chicken bones. Only in the early 1950s did we start to consume chicken on any substantial scale. Today, according to UN Food and Agriculture Organisation, we consume around 73 billion chickens a year (along with 1.5 billion cows and 3.5 billion pigs) – a habit likely to provide rich (and probably confusing) data for those visiting aliens 500,000 years on. The more attentive among them will also note in the fossil record a massive collapse in wildlife and natural biodiversity.

It will not be until August next year at the meeting in South Korea of the International Union of Geological Sciences that the world’s leading geologists will decide whether a formal new Anthropocene epoch has begun, and whether Lake Crawford should be accepted as the “golden spike”. Whatever the conclusion, the Anthropocene Working Group has provided an important reminder that we humans are now a “geological superpower” in the process of changing our planet forever – and not for the better.

David Dodwell is CEO of the trade policy and international relations consultancy Strategic Access, focused on developments and challenges facing the Asia-Pacific over the past four decades