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The issue of erecting a new stratigraphic Epoch encompassing the time since humans had a global effect on the Earth System has irked me ever since the term emerged for discussion and resolution by the scientific community in 2000. An Epoch in a chronostratigraphic sense is one of several arbitrary units that encompass all the rocks formed during a defined interval of time. The last 541 million years (Ma) of geological time is defined as an Eon – the Phanerozoic. In turn that comprises three Eras – Palaeozoic, Mesozoic and Cenozoic. The third level of division is that of Periods, of which there are 11 that make up the Phanerozoic. In turn the Periods comprise a total of 38 fourth-level Epochs and 85 at the fifth tier of Ages. All of these are of global significance, and there are even finer local divisions that do not appear on the International Chronostratigraphic Chart . If you examine the Chart you will find that no currently agreed Epoch lasted less than 11.7 thousand years (the Holocene) and all the others spanned 1 Ma to tens of Ma (averaged at 14.2 Ma). Indeed, even Ages span a range from hundreds of thousands to millions of years (averaged at 6 Ma).
In the 3rd week of May 2019 the 34-member Anthropocene Working Group (AWG) of the International Commission on Stratigraphy (ICS) sat down to decide on when the Anthropocene actually started. That date would be passed on up the hierarchy of the geoscientific community eventually to meet the scrutiny of its highest body, the executive committee of the International Union of Geological Sciences, and either be ratified or not. In the meantime the AWG is seeking a site at which the lower boundary of the Anthropocene would be defined by the science’s equivalent of a ‘golden spike’; theGlobal boundary Stratotype Section and Point (GSSP).
Several options were tabled for discussion and decision, summarised by a 2015 paper in Nature. A case against the erection of an official Anthropocene Epoch on stratigraphic grounds appeared in a GSA Todaypaper in 2016. Despite the fact that there is evidence for the start of human geological, geochemical and biological influences as far back as 8 000 years ago (in effect the Holocene is the Epoch of rapid human growth and transformations), the 2015 paper concludes that there are two candidates for the base of the Anthropocene. The earliest is the decline in atmospheric CO2 that began around 1570 CE and its recovery around 1620 CE recorded in Greenland ice cores. This is suggested to mark a fall in the indigenous population of the Americas from ~60 to ~6 million that followed the completion of European conquest, as a result of genocide, disease and famine. Regeneration of the American forest lands (~5 x 107 hectare) that the dead had once occupied drew down CO2. However this overlaps with the coolest part of the Little Ice Age which may also have resulted in absorption of the greenhouse gas by cooled ocean water. The beginning of the industrial revolution was discounted on the grounds that it was diachronous as well as being difficult to define, having arisen first in Europe at some time in the 18th century. The second candidate was the period when ~500 nuclear weapons were tested above-ground, beginning in 1945 and ending by treaty between the then nuclear powers in 1963. These distributed long-lived plutonium globally, which resides in sediments as a ‘spike’. Around 1963 there are also clear signs that plastics, aluminium, artificial fertilisers, concrete and lead from petrol began to increase in sediments. It is this last option upon which the AWG settled, with 29 members for and 5 against, and is to forward up the ‘chain of command’ in the geoscientific bureaucracy. A detailed and sometimes amusing account of the AWG’s deliberations appeared in the online Guardian newspaper on 30 May 2019.
The decision, in my opinion, signifies that the Anthropocene is an Epoch that includes the future, which is somewhat pessimistic as well as being scientific nonsense. Yet, coinciding as it does with rapidly escalating efforts, mainly by young people, to end massive threats to the Earth System, that can only be welcomed. It is an essentially political statement, albeit with a learned cloak thrown over it. The only way to erase the exponentially growing human buttock print on our home world is for growth-dependent economics to be removed too. That is the only logical basis for the ‘green’ revolt that is unfolding. If that social revolution doesn’t happen, there will be a mass extinction to join the ‘Big Five’, and society in all its personifications will collapse. That is known as barbarism…