Appendix A: a new geological epoch: the anthropocene*
Humankind has been on this 4.5 billion year old planet for only 200,000 years, yet there are disturbing signs that that we have arrived at a new geological epoch in our history because, particularly since the advent of industrialisation in the mid eighteenth century, we have so changed the composition of the earth’s atmosphere and oceans and modified its landscape and biosphere.
Humans living in the industrialised age have spread our “technofossils”: aluminium, plastics, concrete, carbon, particulates (from burning fossil fuels), insecticides and radioactive particles (released by nuclear bombs), widely across the landscape and oceans, permeating the very rock that is forming today. These human activities are so momentous that they have effectively pushed the planet into a new geologic epoch - the Anthropocene – one that is separate and distinct from the Holocene, which began when glaciers retreated 11,700 years ago[1]. It is suggested that 1950 may well prove to be the logical threshold between the two eras.
Humankind’s activities on Earth favouring the declaration of a new geological Anthropocene epoch[2]
- 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).
- 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), ejecting 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.
* Source for header image: Canadian Geographic: "Living in the anthropocene: the human epoch": https://www.canadiangeographic.ca/article/living-anthropocene-human-epoch.
[1].Jan Zalasiewicz, “What mark will we leave on the planet? – A history in layers” which appeared in the Scientific American, September 2016, 24-31; http://www.nature.com/scientificamerican/journal/v315/n3/box/scientificamerican0916-30_BX2.html; see also "When did the anthropocene begin?": http://www.nature.com/scientificamerican/journal/v315/n3/box/scientificamerican0916-30_BX2.html
[2] Ibid.
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