We've been changing the planet for thousands of years
Unique archaeological study takes a new look at land use. Dyani Lewis reports.
Long before people started documenting their own existence, their way of life was already taking a toll on the planet.
Deforestation due to farming and agriculture – activities that are a modern-day blight on Earth’s ecosystems – were making their mark more than 3000 years ago, according to a massive global effort by more than 250 archaeologists, published in the journal Science.
The collaboration, known as the ArchaeoGLOBE project and led by Lucas Stephens while at the University of Pennsylvania and the University of Maryland Baltimore County, US, puts a global spin on a discipline mostly conducted at a local level.
"Many people have realised for some time now that the study of long-term human-environment interactions must include archaeological knowledge, but our research and dataset really open the door to this sort of collaboration at global scale for the first time,” says Stephens.
In order to draw together the many disparate pieces of archaeological knowledge, he and colleagues divided the Earth into 146 analytical regions.
Participating archaeologists fed in information on human land use in those regions at 10 different time points from 10,000 years ago until the year 1850 by completing a detailed questionnaire. More than 700 regional questionnaires were completed, covering all 146 regions.
“It's an interesting example of how archaeologists are starting to use big data,” says palaeoecologist Neil Roberts from Plymouth University, UK, who was not involved in the study.
The picture that emerges is one of increasing impact of humans on their landscapes.
Subsistence lifestyles of hunting, gathering and fishing were commonplace 10,000 years ago, but these were giving way to agriculture and the raising of livestock by 3000 years ago. Agriculture was being practised in nearly half of the world’s regions by that time.
These early impacts on land use are about 1000 years earlier than previous estimates.
That could be down to the type of data used, says Roberts, who wrote a commentary accompanying the paper.
“Archaeology tells you about where people were living, not the area people were not living,” he says, so the Earth’s untouched wilds are largely overlooked.
The authors of the study write that the earlier human-induced changes challenge our notion of when the Anthropocene – the geological epoch marked by human impacts on the Earth’s systems – kicked off.
"It's time to get beyond the most recent paradigm of the Anthropocene and recognise that the long-term changes of the deep past have transformed the ecology of this planet, and produced the social-ecological infrastructures – agricultural and urban – that made the contemporary global changes possible," says co-author Erle Ellis, from the University of Maryland Baltimore County, US.
Clive Hamilton from Australia’s Charles Sturt University disagrees. “Humans scraping the surface of the Earth is in itself not going to transform the functioning of the Earth system, and it has not caused a new geological epoch to come about,” says Hamilton, the author of Defiant Earth: the fate of humans in the Anthropocene.
“They are reducing the Anthropocene to landscape shifts,” he says, instead of the all-encompassing changes to the Earth’s oceans, atmosphere, geology and biosphere that more recent decades have heralded in.
Several different start dates to the Anthropocene have been proposed, dating as far back as the start of the agricultural revolution, more than 12,000 years ago.
In 2019, the Anthropocene Working Group of the International Commission on Stratigraphy, which decides on geological epochs, voted on a start date in the middle of the twentieth century, though a final determination has not been formalised
Regardless of the final determination, the ArchaeoGLOBE project’s contribution can now be held up against other measures of past environmental change, such as pollen and insect records.
"Understanding how humans interact with the environment over the long-term past is one of the best things we can do to help us understand how people will deal with this in the future," says geoarchaeologist Michael Barton of Arizona State University. "We're not starting from zero. We're starting from a long history."