By Roland Pease
BBC Radio Science Unit
We may be witnessing a transformation of the Earth as profound as the end of the age of the dinosaurs, and entering a geological period as distinctive as the Jurassic - and the reason is that we are causing it.
Writing in the house journal of the Geological Society of America, GSA Today, Britain's leading stratigraphers (experts in marking geological time) say it is already possible to identify a host of geological indicators that will be recognisable millions of years into the future as marking the start of a new epoch - the Anthropocene.
Geologists have long divided the Earth's history into distinct epochs, periods and eras - with names as familiar as the Triassic or the Carboniferous.
Transitions between them can be easily recognised, with sharp changes in the fossil record, or in the chemistry of the rocks of the time.
Sometimes the boundaries mark extreme violence.
The end of the Cretaceous Period 65 million years ago, and with it the dinosaurs, and the beginning of the Tertiary (the 'third' age of geology) came with the impact of a huge asteroid.
A force of nature
Sediments around the world from that time carry a tell-tale layer tinged with iridium, a metal more common in space than it is on the Earth's surface.
There can also be soot - the result of global wildfires that followed the catastrophe. The fossil record either side of the boundary is quite distinct.
Plate tectonics, the slow movement of the continents, has also created dramatic changes, as huge mountain ranges are built or ocean basins are cut off or opened up.
New periods are created as the Earth system passes through a new threshold.
But the new epoch has not been shaped by these relentless forces of the deep Earth or the violence of extraterrestrial impacts. Instead, say the scientists, it has been moulded by a single species - man - so that it should be called the Anthropocene, the time of man.
"It's extraordinary how a single species could have such an effect on the whole planet," says Leicester University's Dr Jan Zalasiewicz, who heads the Stratigraphic Commission of the Geological Society, the team that penned the new report.
"Human activity exceeds natural processes in many ways.
"For example, humans emit more CO2 than do volcanoes by quite a long way; humans move more material across the surface of the Earth than do rivers, landslides and floods."
'Blink of an eye'
Bringing an academic rigour to a concept that has been circulating since 2000 when it was first proposed by Nobel Laureate and ozone expert Paul Crutzen, the researchers ask whether there is a worldwide signature that could be recognised long into the future as marking the start of this new epoch.
"What we're asking is what the record in the rocks of the human species is going to look like," says co-author Dr Andy Gale, from the University of Portsmouth.
"It's fascinating thinking what record future geologists will see of human activity.
"For one thing, there will be a hell of a lot of concrete. And the disruption to the Earth's surface, stripped for farming and mining, causing a vast increase in the amount of mud and sand sediment going into the oceans."
"There are other signals," adds Dr Zalasiewicz. "The oceans are acidifying right now. If they acidify much further, coral reefs will stop growing. And so reef limestone will stop being produced. And that will be another very obvious sign in future strata."
Huge changes will occur in the fossil record. Not just because of the mass extinction we are causing, but because of the huge number of human remains that will become melded into future rock layers.
Many of these geological changes stretch out over generations of human history - frustrating attempts to pinpoint the kind of "golden spike" the geologists would like. But even a thousand human generations would be but the blink of an eye in the deep geological record.
"In many rock successions a thousand years can be a millimetre or two," explains Andy Gale.
"So geologically speaking, this series of events is proceeding very fast. I don't think the changes are going to be subtle at all - these signs would be very conspicuous"
Epochs come lowest in the order of geological timescale. By current definitions, we're in the Holocene epoch ("wholly recent") that started at the end of the last ice age. The larger timescales - the periods and eras - are driven by more powerful forces.
The question the geologists are asking is just how big a change we are wreaking on the planet.
You could say the Anthropocene started 200 years ago with the industrial revolution, or 5,000 years ago when sediments started accumulating the first signals of metalwork. But equally interesting is when it will end.
"If humans stop, it won't be that the effects stop. The effects will ramify through the system for a considerable time. If the impacts are big enough, you make whole groups of creatures extinct. And then the future life comes from the survivors, so life changes? and the Earth changes."
This happened when the dinosaurs were wiped out, heralding a new period of Earth history. The comparison is irresistible to the report's authors, including Dr Mark Williams of Leicester University: "We are clearly changing the planet at an exponential rate. And it's possible we could be starting a new geological period and this could be the Anthropocene Period."
Unfortunately to find out, we may need to wait tens if not hundreds of millions of years.