Plastics already enable fine time resolution in deposits via the development of their different types and via the artefacts they are moulded into, and many of these may have long-term preservation potential when buried in strata.
While humans like to call our era on planet Earth the 'Anthropocene', a more fitting name may be the Plasticene - not to be confused with the Pleistocene, the benign period we may now be bringing to a premature end with our industrial pollution.
That's because the main marker humans will leave to endure for millions of years into the future won't be impressive monuments, literature, arts and other works of timeless beauty, a new study shows.
It will, rather, be accretions of long lived plastics incorporated into rocky sediments from land and oceans that we are subjecting to a constant input of plastic waste and detritus.
"Plastics are also pretty well everywhere on Earth, from mountain tops to the deep ocean floor - and can be fossilized into the far future", says Jan Zalasiewicz, Professor of Palaeobiology from the University of Leicester's Department of Geology, an author of the study published this week in the journal Anthropocene.
"We now make almost a billion tons of the stuff every three years. If all the plastic made in the last few decades was clingfilm, there would be enough to put a layer around the whole Earth. With current trends of production, there will be the equivalent of several more such layers by mid-century."
Plastic, not beauty, is eternal
The study suggests that the surface of the planet is being noticeably altered by the production of long-lasting man-made materials, resulting in us entering an 'Age of Plastic', or Plasticene.
Plastics have such a long-lasting impact on the planet's geology, it says, because they are inert and hard to degrade. As a result, when plastics litter the landscape they become a part of the soil, often ending up in the sea and being consumed by and killing plankton, fish and seabirds.
Moreover they can travel thousands of miles, caught up in the 'great oceanic garbage patches', or eventually being washed up on distant beaches. Plastics can eventually sink to the sea floor in even the most remote parts of the globe, to become a part of the geological strata of the future.
And the process is not about to stop, says Zalasiewicz. First, the production and use of plastics is on an exponential upwards trend worldwide. But even once humans die out, our plastic residues will continue to spread around the planet:
"Plastics will continue to be input into the sedimentary cycle over coming millennia as temporary stores - landfill sites - are eroded. Plastics already enable fine time resolution within Anthropocene deposits via the development of their different types and via the artefacts, known as 'technofossils', they are moulded into, and many of these may have long-term preservation potential when buried in strata.
"Once buried, being so hard-wearing, plastics have a good chance to be fossilized - and leave a signal of the ultimate convenience material for many million years into the future. The age of plastic may really last for ages."
'A key geological indicator'
The rise of plastics since the mid-20th century, both as a material element of modern life and as a growing environmental pollutant, has been widely described. Their distribution in both the terrestrial and marine realms suggests that they are a key geological indicator of human industrial civilisation, as a distinctive stratal component.
"We have become accustomed to living amongst plastic refuse", observed co-author Colin Waters from the British Geological Survey. "But it is the 'unseen' contribution of plastic microbeads from cosmetics and toothpaste or the artificial fibres washed from our clothes that are increasingly accumulating on sea and lake beds and perhaps have the greatest potential for leaving a lasting legacy in the geological record."
And it is the very novelty of plastics that will make them a unique geological marker, says field archaeologist Matt Edgeworth, who also participated in the study: "It may seem odd to think of plastics as archaeological and geological materials because they are so new, but we increasingly find them as inclusions in recent strata. Plastics make excellent stratigraphic markers."
"Plastics were more or less unknown to our grandparents, when they were children", adds Zalasiewicz. "But now, they are indispensible to our lives. They're everywhere - wrapping our food, being containers for our water and milk, providing cartons for eggs and yoghourt and chocolate, keeping our medicines sterile. They now make up most of the clothes that we wear, too.
In 2016 the Anthropocene Working Group led by Professor Jan Zalasiewicz will gather more evidence on the human era to help decide whether and how this new time unit should be formalized.
The study: 'The geological cycle of plastics and their use as a stratigraphic indicator of the Anthropocene' is published in Anthropocene.
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