Enter the Anthropocene?
Near reaching the end of our journey, it is time to consider the impact of humankind’s sojourn on Earth. What kind of footprint have we left behind? The possibility of an Anthropocene era has been mentioned, but purely in passing[1]. The term Anthropene was coined originally because mankind and in particular industrialised humanity has changed the composition of the earth’s atmosphere and oceans and modified the landscape and biosphere.
Thus, humans living in the industrialised age have spread:
And that is by no means all the evidence:
All this constitutes powerful evidence favouring the declaration of a new Anthropocene epoch[2]. But even assuming this array of evidence to be exactly as stated, questions still abound:
For practical purposes, the most enticing boundary would seem to be the extraordinarily great acceleration of population, energy use and industrialisation that began in the mid-1900s. This is the era marked by strong rises in concrete, plastics, plutonium and their consequential effects[4]. But to make a case that we are in the midst of such an Anthropological era, scientists would need to show that human impacts will leave a clear mark fossilised in strata that could be readily recognised tens or hundreds of millions of years from now by geologists in the far future.
As Jan Zalasiewicz points out in his article, the focus on strata is important, because to a geologist, geologic strata equal geologic time. Is there enough evidence for this and should an earth that is rapidly, profoundly and permanently being transformed by humans be formally recognised as a new epoch in the geologic timescale? In other words, does all this constitute geologic change, change so profound that its signals are imprinted into geologic strata across the planet, and if so where are the indicators?
The geologists who will make this determination now and in the future are on the lookout for such things as radioactive nuclei or carbon particles trapped in the snow and ice layers of Greenland and Antarctica, in sediment layers in far-flung lakes and fjords and undisturbed seafloors, but for the time being the jury is still out[5].
[1] The Paleocene and Eocene periods and beyond
[2] This is an edited summary of an article by Jan Zalasiewicz entitled “What mark will we leave on the planet? – A history in layers” which appeared in the Scientific American, September 2016, 24-31
[3] Ibid, 26-28.
[4] Ibid, 31.
[5] Ibid.
Header source: Segment from a graphic in Jan Zalasiewicz's article referred to in [2] above, reproduced at http://www.nature.com/scientificamerican/journal/v315/n3/box/scientificamerican0916-30_BX2.html
Thus, humans living in the industrialised age have spread:
- aluminium (more than 500 million metric tons processed since World War II) and other mineral compounds until the stage has been reached where pure aluminium “is becoming part of modern sediment layers”;
- plastics (more than 300 million metric tons produced annually, the detritus being found not only on land but also in the oceans where it is consumed by marine life, ending up in the muds of the sea floor when the animals which have consumed it die);
- concrete (“the signature rock of the Anthropocene”, about a kilogram for every square metre of the earth’s surface and broken up fragments now common beneath our towns and cities).
And that is by no means all the evidence:
- carbon dioxide caused by the burning of fossil fuels in the atmosphere since the industrial revolution began now occurs at a rate about 100 times faster than the rate of rise when the glaciers retreated at the start of the Holocene;
- carbon from burned fossil fuels rich in the carbon isotope C12 is being absorbed by plants and animals leaving a permanent C12 mark of the Anthropocene;
- nitrogen fertilisers used since the beginnings of agriculture 10,000 years ago infiltrate the soil and water and leave clear chemical signatures, lakes at high altitudes become polluted, fertiliser runoff from farm fields filters into streams and rivers and then travels out to sea;
- tiny radioactive particles that spread around the globe after every nuclear bomb explosion (wartime apart, more than 500 in the atmosphere between the mid-1940s and the late 1960s), ejected rare isotopes of plutonium (239 and 240) that settled globally, leaving particles in the soil and polar ice that were absorbed by animals and plants at the surface; n perhaps 100,000 years they will have decayed to a layer of uranium 235.
All this constitutes powerful evidence favouring the declaration of a new Anthropocene epoch[2]. But even assuming this array of evidence to be exactly as stated, questions still abound:
- When did this so-called era start, and are these changes so profound that their manifestations are likely to be imprinted into geologic strata throughout the planet?
- Will they leave permanent signatures in geological layers of rock defining formal epochs and eras?
- Could it be that humans are really wreaking change as dramatic as the transformation that started the Holocene 11,700 years ago when extensive glaciers covering much of the earth were retreating and melting so much they raised sea level globally by 120 metres.
- Could the results of human habitation over only a few centuries really be measured alongside “the great shifts of our planet’s tumultuous geologic past” where time units are measured in millions and even billions of years?[3]
- When, moreover, would such an era have commenced - thousands of years ago, when human impacts were first discernible, or only at some future time when the full impact of human exploitation will have played out?
For practical purposes, the most enticing boundary would seem to be the extraordinarily great acceleration of population, energy use and industrialisation that began in the mid-1900s. This is the era marked by strong rises in concrete, plastics, plutonium and their consequential effects[4]. But to make a case that we are in the midst of such an Anthropological era, scientists would need to show that human impacts will leave a clear mark fossilised in strata that could be readily recognised tens or hundreds of millions of years from now by geologists in the far future.
As Jan Zalasiewicz points out in his article, the focus on strata is important, because to a geologist, geologic strata equal geologic time. Is there enough evidence for this and should an earth that is rapidly, profoundly and permanently being transformed by humans be formally recognised as a new epoch in the geologic timescale? In other words, does all this constitute geologic change, change so profound that its signals are imprinted into geologic strata across the planet, and if so where are the indicators?
The geologists who will make this determination now and in the future are on the lookout for such things as radioactive nuclei or carbon particles trapped in the snow and ice layers of Greenland and Antarctica, in sediment layers in far-flung lakes and fjords and undisturbed seafloors, but for the time being the jury is still out[5].
[1] The Paleocene and Eocene periods and beyond
[2] This is an edited summary of an article by Jan Zalasiewicz entitled “What mark will we leave on the planet? – A history in layers” which appeared in the Scientific American, September 2016, 24-31
[3] Ibid, 26-28.
[4] Ibid, 31.
[5] Ibid.
Header source: Segment from a graphic in Jan Zalasiewicz's article referred to in [2] above, reproduced at http://www.nature.com/scientificamerican/journal/v315/n3/box/scientificamerican0916-30_BX2.html