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Geological timescale is divided into eons, which are further sub-divided in descending order into eras, periods, epochs and ages.
The decision to move to a new time period is based on a major occurrence on Earth evidenced in rock layers (strata) and the fossils within them.
For example, extinction of the dinosaurs 66 million years ago heralded a move from the Cretaceous to the Paleogene period.
Presently we are in the Holocene epoch, ongoing since the world emerged from the last ice age some 11,650 years ago.
Many people however, myself included, have used the term ‘Anthropocene’ – derived from Greek and meaning the ‘recent age of man’ – to describe the present geological epoch, because of the effects we humans are having on the planet, particularly air, sea and land pollution, animal extinctions and climate change.
Transition from the Holocene to the Anthropocene epoch may seem obvious, but the earliest it can be approved is in 2024 when the International Commission on Stratigraphy meets to consider the evidence.
Nevertheless, some scientists believe that the Anthropocene is well underway, beginning perhaps with the industrial revolution in the 1800s, the testing of atomic bombs in 1945, or in 1950 when human activity on the planet markedly accelerated.
Presently, the Anthropocene Working Group is considering a number of signals at particular sites to identify the best global marker of human impact, the so-called golden spike, that demonstrates the onset of the Anthropocene.
There are several contenders for this accolade, including environmental plutonium from nuclear weapon testing; microplastics and concrete in sediments; and methane in ice cores from burning fossil fuel.
Also on the list are rising animal extinctions as well as indications of intensive farming and fishing such as fossilised chicken bones in land-fill sites, increased nitrogen and phosphorus from fertilisers in soils and fish scales in lake and sea sediments.
But there are issues with all these suggestions.
Plutonium contamination pinpoints a precise boundary, but does it have a permanent global impact? In contrast, methane, concrete, and markers of intensive farming may have less well-defined onsets, but are clearly major contributors to man-made climate change.
Obviously we must await the outcome of the commission’s deliberations, but the declaration of a new epoch would highlight our reckless behaviour and perhaps encourage positive action to confront climate change before it’s too late.