Humanity has become such a force within the earth system that our activities, from the combustion of fossil fuels to the dropping of nuclear weapons to even the global spread of the domestic chicken, have caused the planet to enter a new geological epoch termed the Anthropocene.
This is the conclusion this week of a group of scientists assigned to assess the concept, already widely adopted within the social sciences, humanities and the popular press, but yet to be formally approved by the International Union of Geological Sciences (IUGS) or its lower level body, the International Commission on Stratigraphy, whose job it is to precisely define the units (periods, epochs and ages) of the geologic time scale.
The Anthropocene concept, “is geologically real”, they conclude, and is of sufficient scale to be incorporated into the International Chronostratigraphic Chart, the formal categorisation of geologic time. Chronostratigraphy uses evidence contained in layers of rock layers, ocean sediments, and ice cores, or ‘strata’ in relation to time to determine the planet’s geologic history.
When first suggested by atmospheric chemist Paul Crutzen and the late biologist Eugene Stoermer in 2000, the pair intended that the term describe the period following the Industrial Revolution. Since that time, humanity has increased the amount of carbon dioxide by 30 percent—a concentration not experienced in 400,000 years.
But as the working group began their deliberations, other human-caused or ‘anthropogenic’ effects—such as the damming of rivers, a surge in mining 3,000 years ago, and methane emissions since the dawn of agriculture 10,000 years ago—began to also be considered as signatures of the start of the Anthropocene. However, they concluded that neither these earlier transformations nor the Industrial Revolution were significant enough on a global scale to have left the sort of clear geological markers that stratigraphers require for delineation of a new geological unit of time.
Instead, the start of the Anthropocene was in the 1950s, the launch of what the International Geosphere-Biosphere Programme has termed the ‘Great Acceleration’, when the Earth experienced a marked increase in rates of erosion, large-scale perturbations of the carbon, nitrogen and phosphorus cycles, a step-change in global warming and sea level rise, and unprecedented levels of movement of species across different parts of the planet. Climate change thus is only one element of the radical changes humanity has wrought.
This date also coincides with what the researchers argue should be recognised as clear geological markers in rock layers such as plastic, radionucleotides from atom bomb tests, and the fossilizable remains of chickens.
However, the concept has been controversial amongst some geologists who have worried that the working group included scientists beyond their discipline, that the evidence in the rock strata is weak, and that the concept is more an environmentalist political weapon than hard science. The IUGS must still vote on the recommendations from the working group before the Anthropocene is formally ratified.
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