When exactly did the human age begin?

In the search for a precisely defined starting point of the Anthropocene – the geological era of man – geologists have shortlisted twelve sedimentary sequences. They want to use one of these drill cores as a kind of reference to mark the beginning of the human age. A preliminary decision should be made by the end of this year, write Colin Waters and Simon Turner in the journal Science. The two researchers are at the head of the group of experts (Anthropocene Working Group; AWG) that is to determine the reference sample.

Humans have already changed nature greatly

Geologists divide the earth’s history into different eras. Accordingly, humanity is currently living in the Holocene, which began almost 12,000 years ago after the end of the last ice age. However, the AWG experts are of the opinion that the Holocene ended in the mid-20th century. The basis for this is that changes in nature, in the atmosphere, in the soil and in the sediments are largely due to human activities – and leave permanent geological traces.

The term “Anthropocene” was coined in 2000 by the US biologist Eugene Stoermer and the Dutch meteorologist and Nobel Prize winner Paul Crutzen, former director of the Max Planck Institute for Chemistry in Mainz to highlight the immense – mostly negative – influence of mankind on the earth. However, the Anthropocene has not yet been confirmed as an official epoch. The definition of a reference sediment profile is a step in this direction.

It is obvious that mankind has had a massive impact on our planet since the beginning of industrialization at the latest. The atmosphere is warming, sea levels are rising, entire ecosystems have disappeared. Industry and agriculture are shifting cycles of carbon, nitrogen and phosphorus, for example. Substances such as plastic, aluminum and concrete particles find their way into the environment on a global scale. Some animal and plant species are spreading far beyond their original areas, while others are dying out.

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Various drill cores should provide information in the definition

This change is also visible and measurable in the sediments, because certain substances from the water or the air are deposited there over time. This allows experts to follow how the earth is changing on the surface. So-called markers include radioactive fallout from nuclear weapons tests, fly ash from industrial production or the ratio of certain nitrogen isotopes. The latter indicates changes in the nitrogen balance, i.e. over-fertilization due to the start of industrial agriculture, as Reinhold Leinfelder, Emeritus at the Free University of Berlin, explains. He is also a member of the AWG Group.

The twelve drill cores that are now shortlisted were deliberately taken from very different ecosystems so that the new frontier can be identified everywhere. There is one from the sediments of the Baltic Sea, from a coral reef off Australia, from the bottom of a Canadian lake, an ice core from Antarctica and a sample from a peat area in Poland. “Taken together, the 12 sites offer a diverse perspective on the geological reality of the Anthroprocene,” write Waters and Turner.

All samples have in common that they consist of layers of sediment or ice cores that have gradually built up over the past decades. The markers are chosen in such a way that their concentration increased sharply at a certain point in time around the middle of the century – and this change can also be measured at a certain point in the drill cores. One or more such particles or substance concentrations, which are appearing for the first time or are also rapidly increasing, are intended to define the formal start of the Anthropocene as primary markers.

The human age is not yet on the geological time scale

The search is now on for the drill core that has the ideal prerequisites as a reference sample. “Ideally, the sample site would provide precisely dateable strata with a resolution to pinpoint the beginning of the Anthropocene to a specific year,” Waters and Turner write to be able to describe – in contrast to the relatively stable Holocene.

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“The definition of a geological time period with such reference profiles is standard, so that geologists all over the world have the same understanding of the respective time period and reference profiles can also be examined by others again and again,” explains Leinfelder.

However, it may still take some time before the human age is actually taken over into the geological time scale. The reference proposal still has to be approved by several committees. First by the Subcommission on Quaternary Stratigraphy (SQS), then by the International Commission on Stratigraphy (ICS), and finally by the Executive Committee of the International Union of Geological Sciences (IUGS).

RND/dpa

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