Plastic bottles, smartphones, chicken bones – and the wider debris of everyday life – are tipped to outlast human civilisation and become the defining fossils of our age.
Fossils are usually associated with dinosaur bones or ancient sea creatures preserved in stone. But scientists now believe that modern waste – from polyester clothing to electronic devices – is writing an entirely new chapter in Earth's geological story.
As these everyday items are buried and compressed over millennia, they’re forming what experts call technofossils – distinctive markers of human civilisation that could outlast our species by millions of years.
In the far future, a thin but unmistakable layer is expected to appear in Earth's rock record – a stratum built from materials engineered to resist decay.
"If some future civilisation were to dig into rocks that are a million-years-old and they came across this layer, the Anthropocene [era] that we are now creating, I think one of the most clear relics will be that of plastics," palaeontologist Sarah Gabbott told RFI.
"Plastics are, first of all, absolutely everywhere across the globe. This is in terms of general litter – things like water bottles and plastic bags – but also, of course, really famously in the form of microplastics, which are airborne."
Messages in a bottle
Gabbott and her University of Leicester colleague, Jan Zalasiewicz, have spent their careers examining the fossil record of ancient life. Now they've turned their expertise to predicting how today’s discarded items might appear to future scientists.
Their new book, Discarded: How Technofossils Will be Our Ultimate Legacy, examines the geological footprint humans are creating. Unlike natural materials, much of what we produce is made to endure – not to break down.
When asked whether future geologists might mistake plastic waste for natural geology, Gabbott explained why this is unlikely.
"Plastic is incredibly durable. We argue in the book that not only will the plastic be there chemically, but it will be the shapes. There will be things like computer screens, things like mobile phones – shapes that in nature just do not exist. A lot of rectangles and a lot of complexity as well," she said.
These unnatural geometries – the right angles, sharp edges and perfect circles of manufactured items – would be unprecedented in the fossil record.
While natural fossils follow organic patterns – the spiral of an ammonite, the branching of coral, the curves of bone – technofossils will reveal a world of straight lines and standardised forms.
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That artificial complexity, Zalasiewicz added, goes beyond just form. It includes a mix of materials that rarely, if ever, occur together in the natural world.
“If you consider all the things that plastic is bound up with – materials that don’t occur in biological systems or even commonly in geological ones – it becomes even more striking,” Zalasiewicz said.
“Take metals, for example. Pure metals are quite rare in nature. There are a few exceptions like gold, but we’ve purified huge amounts of aluminium, iron, chrome and others.”
These metals, Zalasiewicz explained, are now tangled up with plastics and other human-made materials like concrete, forming a new class of objects.
“Some of those metals will survive. They’ll leave behind a clear signal – an explosion of metal production, completely unlike anything biology produced over the past three or four billion years.”
The chicken legacy
The most abundant bird on Earth today isn't a wild species but the humble domestic chicken – with 75 billion slaughtered annually for human consumption.
These birds are expected to leave behind one of the most distinctive and revealing fossil records of the Anthropocene.
"The first thing that will really stand out will be just the sheer abundance of this one animal compared with all other animals," Gabbott said.
Unlike natural fossilisation, which typically preserves only a tiny fraction of organisms, modern waste disposal systems create concentrated bone repositories. Landfills – with their oxygen-poor, plastic-lined chambers – function as inadvertent fossilisation factories.
"We typically put the bones and other materials within plastic-lined holes in the ground," Zalasiewicz explained. "These masses usually become dehydrated, with things like bones – and even flesh – becoming mummified."
Beyond their sheer numbers, these chicken bones bear distinct markers of industrial farming – skeletal deformities that stand to baffle future paleontologists.
"They're going to see bones that are kind of deformed. Some of them have osteoporosis," Gabbott said.
"An average chicken from hatching to being slaughtered is between only five and seven weeks old, and we've genetically engineered them to grow so fast that their bones can't take the weight."
To future scientists, these fossils may offer more than anatomical insight. Their condition could help reconstruct the industrial systems that shaped them – and the pressures placed on animals in a human-dominated world.
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Mysterious rectangles
Among all our technofossils, smartphones may present the most enigmatic puzzle to future palaeontologists.
These ubiquitous devices – billions produced annually, then discarded within years – will leave behind countless rigid rectangles filled with rare metals, circuit boards and glass panels.
Many are already being buried in landfills and sediment.
"If you think about a mobile phone, you've got this rectangular shape with materials that never occur together in nature," Gabbott said. "But in terms of what they were used for, in a million years, they're not going to give that much away."
The transformation of materials over geological time will further obscure their purpose.
"The glass becomes opaque over time," she added. "Future civilisations will know these objects were numerous and important to us, but their function might remain a complete mystery."
Even more perplexing may be the remnants of our renewable energy infrastructure.
Zalasiewicz described how vast composite blades from wind turbines – difficult to recycle – are already being preserved underground.
"The blades are cut into lorry-sized sections and stacked in their own landfill sites. If they re-emerge in the side of a cliff someday, deciphering their original form and purpose would be an extraordinary challenge – like finding fragments of an alien technology," Zalasiewicz said.
Science of prediction
So how are scientists able to forecast the fate of materials over millions of years? Gabbott and Zalasiewicz combine laboratory testing with clues from Earth's existing fossil record.
"We've only really had plastic in any abundance since the 1950s and 60s," Gabbott explained. "We haven't had it long enough to know exactly what will happen to it."
To bridge this gap, they look to comparisons in nature – such as green algae that produce plastic-like polymers in their cell walls.
"Some of these algae with their polyethylene-like substances have fossilised from over 50 million years ago," Gabbott said.
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Concrete, now the most abundant human-made material on Earth, also leaves clear geological traces. Zalasiewicz points to its durability, especially in its simplest ingredients.
"We've made more than half a trillion tonnes of it – enough for a kilo of concrete for every square metre of the Earth, land and sea," he said.
While some components of concrete may change, others will remain recognisable.
"The sand and the pebbles within the concrete – they will stay much the same, because we've got examples of those from billions of years ago," Zalasiewicz added.
"Overall, I think we have a good idea of what our future explorers – our future aliens – will see.”
