Indelibly Stamped

Photo by Elena Mozhvilo on Unsplash

Next year is a big year for geologists.

Because next year, a small group of geologists will decide, on behalf of science, when (or if) humans have permanently changed our planet in a way that will still be visible millions or billions of years hence.

You may well be asking yourself one (or both) of these questions: ‘why is that a small group of geologists get to make this call?’; and ‘why should I care?’

I’ll try to answer both questions but what I can’t do is to convey the drama, intrigue and skulduggery behind what may seem to be a finely balanced, somewhat lofty and detached decision to be made by some mild-mannered scientists in slightly dusty jackets but is in fact a high-stakes, politically charged, vigourously fought melee worthy of a Netflix boxed set.

Planet Earth is old. Really old. To make sense of it, this huge span of time is split into sections which are split into subsections and so on. Some of the names of these sections are familiar. For example, the film Jurassic Park is named after the Jurassic Period famed for its dinosaurs (small point – most of the dinosaurs in the film actually lived in the Cretaceous Period – never mind). The rocks out of which Swaledale was carved all come from an older period – the Carboniferous – known for its swampy forests which eventually turned into coal.

And this is where geologists come in. A period is typically defined by the fossils of the plants and animals alive at the time. The boundary between two periods is usually marked by a major change in the fossils found in the rock record of Earth’s past, and because geologists are in charge of all things rocky, geologists get to decide when the rocks show a major change of direction for our planet worthy of a new period of time. What applies to the ancient past also applies to recent times, which is why geologists get to say if a new period, brought about by humans, has now started. Why just a ‘small group’ of geologists? That’s just how geologists work.

To be precise, next year’s decision is not about a new period, but about a new epoch (in the jargon, periods are divided into epochs). Our current period is called the Quaternary period which started 2.6 million years ago. Our current epoch is the Holocene which started 11,700 years ago, when the last Ice Age ended. What geologists are deciding is whether the Holocene is now over, and we have entered a new epoch, the Anthropocene (from the Greek Anthropos, meaning ‘human’).

It’s worth pausing for a moment to reflect on what announcing a new period, or epoch means. These divisions of time reflect massive upheavals to the Earth system, literally (in the case of the meteor that wiped out the dinosaurs) earth-shattering. Geologists have already agreed that humans have brought about a change of similar significance which is no minor matter. Next year’s meeting is to decide not if, but exactly when it happened.

There have been two main candidates for the start of the Anthropocene. The first trigger is the global goings on following Columbus’ voyage of 1492, uniting the old and new worlds. We were never taught the scale of the consequences of this event at school. For one thing, the remains of domesticated plants and animals quickly distributed around the world. Maize pollen turns up for the first time in Italian muds and horse bones suddenly appear all over America. Global trade ensued, and the slave trade, coupled with sugar and other produce grown in the Americas pushed enough calories into the United Kingdom to fuel the industrial revolution and all that followed. The arrival of Europeans also caused the death of 95% of the native American population. The resulting complete collapse of the extensive farming communities across central and south America led to a regrowth of forest which has left a fingerprint in the carbon dioxide levels recorded in ice cores.

The second candidate is the ‘Great Acceleration’. Triggered by the widespread and industrial scale exploitation of fossil fuels, and the re-alignment of global trade and politics following World War Two, the 1950s saw a rapid gear change in human impacts on the planet, and as these impacts scaled up, a corresponding decrease in the planet’s ability to absorb them. We all know the signals: carbon dioxide, ocean acidification, loss of biodiversity, deforestation, nitrogen, plastic, global warming, but it’s still shocking to see them reflected as graphically as they are in the International Geosphere-Biosphere Programme’s (IGBP) planetary dashboard ( ), which highlights the upturn in these trends from the 1950s. Many aspects of the Great Acceleration will leave a long-lasting geological footprint but the marker of choice is likely to be the peak in atmospheric radiation shortly after the 1953 nuclear Test Ban Treaty.

As you might imagine, in addition to these two candidates, other opinions are available. Some argue that human impact started much earlier, and that the Holocene and Anthropocene are one and the same. Others argue that it is too soon to identify a suitable marker of humans’ impact: something much more significant or devastating is just round the corner. Traditionalists point out that new epochs are usually marked by the appearance of new species (and so new fossils in the rocks) yet to emerge. And of course there are plenty of voices (including geologists working in oil and gas) claiming that this is all nonsense, the human impact on the planet is insignificant. 

Which leads on to the second question: why does all this matter? What science says plays a significant role in legitimising the stories people live their lives by, especially when endorsed by public leaders. The decision these geologists make will feed into the public perception of environmental concerns. For example, if the chosen marker is Columbus’s blip in the carbon dioxide trace, the urgency of the climate emergency will be amplified. If, on the other hand, the chosen marker is a peak in atmospheric radiation caused by nuclear tests, it will be easy for proponents of business-as-usual to say ‘We’ve already dealt with that. Nothing to see here’.

As I write, it looks like the Anthropocene will be deemed to have started in the 1950s. Next year’s meeting will principally be a technical choice concerning which signal of nuclear weapons testing most suits the needs of geologists for an unambiguous and indelible stamp on our planet. To be sure, geologists are keen to point out that what they choose as a marker is not necessarily the most significant consequence of the change they seek to record. But they also know that the impact of whatever they decide will extend way beyond the boundaries of geology.

Further Reading

I wrote this blog after reading ‘The Human Planet: How We Created the Anthropocene’ (Pelican Books) by Simon Lewis and Mark Maslin. They make an eye-opening and very persuasive case for choosing Columbus as the trigger for the Anthropocene. There are many articles online presenting every conceivable angle on the debate.

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