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Rekha Dixit
Rekha Dixit


Our existence will be recorded as a time of dramatic environmental change

Interview/ Colin N. Waters, secretary, Anthropocene Working Group


The Anthropocene Working Group, a body of 33 scientists, is tasked with finding that line on the rock which will mark the beginning of the Anthropocene. Geologist Colin N. Waters explains to THE WEEK just what this geological hunt entails. Excerpts from an interview:

Why is it necessary to have a new geological time period named after man?

The name anthropocene was coined by Paul Crutzen. The name may be a label, but it reflects the fact that humans are the dominant force driving changes to key earth processes. But not all geological time periods have logical names; the Silurian and Ordovician are named after obscure ancient Welsh tribes who were certainly not around 400 to 500 million years ago.

The key issue for us is the ultimate effects of these changes. If they are permanently written in sediments or glacial ice as a signal that is every bit as large, or even larger, than other changes to the Earth over geological time, it would be remiss not to record it as a geological unit. In many millions of years time, looking back at the present, when there will likely be no notion of the nature of human civilisation or culture or politics, the evidence of our existence will be recorded in the rocks as a time of dramatic environmental change. Will the future observer be able to discern whether the cause of these changes was human activity is less certain.

What difference will a formal nomenclature make?

The Geological Time Scale that summarises the last 4.5 billion years of earth history into episodes of biological, chemical or physical change is a fundamental part of geosciences. The terminology it uses has developed through rigorous scientific investigation and provides a common standard. At present, without formal definition, the term is being used loosely, based on different perceptions of what it should mean.

How did the working group recommend 1950 as the beginning of Anthropocene?

The AWG looked at a broad range of environmental signals. Some such as plastics, aluminium and concrete are novel materials that have only become abundant since about 1950. Black carbon and fuel ash appeared earlier with the Industrial Revolution, but both show a dramatic abundance—1970 for black carbon and 1950 for the spheroidal fuel ash particles. Ice core records show clear increase in nitrates (from fertilisers) and greenhouse gases like carbon dioxide and methane in this period. Radionuclides from atmospheric nuclear testing tend to make an appearance globally in sediments and ice from about 1952, peaking in 1964. All these signals cluster around mid 1900s.

Why not name Anthropocene from the beginning of agriculture or Industrial Revolution?

To argue that we have left the Holocene, we need to show that earth systems are no longer in a Holocene state. The scale of changes for most key signals (until the mid-20th century) are typically well within the normal range of variation during the Holocene and in many cases, built up gradually. Agriculture has multiple areas of origin but took millennia to migrate globally. Can one say when precisely agriculture started? There is no one agricultural event that can be identified as being almost globally synchronous until the introduction of artificial fertilisers and pesticides in the 20th century. The Industrial Revolution starts as a western European event that takes decades to gradually cross the planet; its expression in India is markedly different to that in the UK.

We are not equating the Anthropocene with the start of anthropogenic impact, which is highly variable between regions of the planet. The start of the geological Anthropocene needs to be isochronous, starting at the same time everywhere, and the signals during the mid 1900s come closest.

How is the 33 member AWG looking for the line on the rock?

We are just starting on how we intend to look for the sections that could be used to be fixed as the marker. We are looking at environments like marine and lake sediments, glacial ice, cave deposits, even corals and trees where we should be able to study annual growth rings that record environmental changes. We may use existing core (rock or ice) collected for other purposes, or we may need to collect new cores. I am coordinating the exercise to examine existing research activities and use them to determine the most suitable geographical locations.

The working group prefers radionuclides as the marker for the Anthropocene. But there are several other candidates, too.

How long will formalising the Anthropocene take?

This process isn’t normally given precise time constraints. But given the keen interest, the aim is to have the evidence available in time for the 36th International Geological Congress in Delhi in 2020.

After the proposal is approved by the sub commission on Quaternary Stratigraphy, it will to go up to the International Commission of Stratigraphy which comprises chairs of all the geological periods. If they vote in favour, it will go for approval to the International Union of Geological Sciences. This process can also take some considerable time.

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The Week

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