英媒：美元上周表现为逾一年来最糟 受政治不确定性拖累

When tomorrow comes, what will remain of our towns and cities, of supermarkets and shopping malls (and everything that’s in them), of roads and airports and harbours? Will there, indeed, be anything to find and study – or will everything have mouldered away?

As palaeontologists, we have spent our careers studying the fossil remains of the past: bones, shells, and carapaces from up to half a billion years ago. Now we have applied that knowledge to working out what is going to happen to our modern constructions, of plastics, steel and concrete. Many of these artefacts of today, like ballpoint pens, subway tunnels and mobile phones, will become, we think, the technofossils of a far tomorrow.

Fossilization is the preservation of the remains of animals and plants, or of the physical traces that they make like footprints and burrows, in rock strata. One factor that helps fossilization is abundance, with common organisms getting into the fossil record more frequently than rare ones.

Presently, the dizzying production of modern materials tilts the scales in favour of their future fossilization: more than 10 billion tons of plastics have been produced in the last 70 years, and over half a trillion tons of concrete. The manufactured world as a whole, in that time, has grown to outweigh all of the living things on Earth combined.

And, these materials are designed to be hard-wearing, to resist wind and rain and decay. Once they are no longer useful to us and are discarded, those properties remain. And, very often, we simply bury our discarded waste objects, in burgeoning landfill sites. In beginning this journey through time, our discarded artefacts can still interact with the living world, some being swallowed by birds, others entangling fish or releasing toxins. Such effects on the wider environment can persist for many years. Even deeply buried, our waste can affect groundwater and create new mineral growths. 

In trying to use the geological past as a guide to the far future, one obstacle is the plethora of new minerals and new materials that human ingenuity has produced, substances that have no geological pedigree at all – and mostly no archaeological one either. Thus, the Earth has about 5,200 natural minerals – but humans have now created more than 300,000 synthetic mineral compounds. Very few have been considered as regards to their longevity.

Synthetic plastics are a new, and now abundant material, essentially a post-1950 phenomenon. Published estimates of how long they might endure typically quote a few centuries, most being no more than educated guesses. And modern observations show that at the surface and in the presence of sunlight and oxygen, plastics slowly degrade – but mostly into scatterings of microplastic debris. Where protected from these agents of plastic decay, little change is seen. But observations so far cover only a matter of decades, not millions of years – and this is where palaeontology can give insights.

Living in the seas today is a microscopic marine alga, called Tetraedron, which secretes a tough outer wall of a biopolymer that chemically closely resembles synthetic polyethylene. In the 48 million-year-old strata of the Messel shales of Germany one can find fossil Tetraedron specimens which, moreover, have retained their plastic-like chemical structure. It’s giving a clue that, once buried and protected from sun and air, at least some of our fossil plastic discards can endure over truly geological timescales.

One can make more such comparisons. The synthetic cement that binds modern concrete is rich in minerals that are rare in nature; over time, these will likely transform into more common minerals. But the sand and gravel that give concrete its framework are among nature’s most resistant materials that can keep their form for billions of years underground. The silicon of our silicon chips is vanishingly rare in nature, but may transform into the silica of common quartz – though the information within their nano-scale architecture will likely be lost. The paper pages of our books, with their inked messages, have a better survival chance, for they are composed of plant material that we know can fossilize exquisitely. 

Thousands of years from now, a rich and stupendously diverse record of our modern infrastructure will be present worldwide, dwarfing the archaeological record we now study, of our pre-industrial ancestors (though future archaeologists may need to explore underwater too, among remains of coastal megacities drowned by sea-level rise).

Hypothetical chroniclers, tens to hundreds of millions of years hence, will need to seek our record in strata, exposed in cliffs and mountainsides, much as we dig for dinosaur bones today. They, too, would encounter rich, complex technofossil accumulations, to surely amaze and perplex them – and make them ponder, deeply, the species that constructed them.