Mohi Kumar writes:

When we think of how humans have altered the planet, greenhouse gas warming, industrial pollution, and nuclear fallout usually spring to mind. But now, a new study invites us to think much further back in time. Humans have been altering landscapes planetwide for thousands of years: since at least 1000 B.C.E., by which time people in regions across the globe had abandoned foraging in favor of continually producing crops.

“This is the first project of its kind within archaeology,” says Lucas Stephens, an archaeologist and environmental researcher at the Environmental Law & Policy Center in Chicago, Illinois, and the lead author of a study that presents the expert opinions of hundreds of archaeologists around the world. “There’s never been a global synthesis like this.”

Scientists have long sought to model ancient land use to accurately inform modern climate reconstructions and to set a start date for when humans first made their mark on the planet. The most commonly used model, however, uses estimates of estimates: It takes other scientists’ guesses of the human populations of various regions, then estimates how much land would be required to sustain them. That model places the start date for continuous global farming at only 500 years ago.

To pinpoint a more accurate date, researchers divided Earth’s land into 146 regions covering every continent except Antarctica. They then invited more than 1300 archaeologists with expertise in ancient land use to complete a roughly 80-question survey, asking how humans in each region used land for the past 10,000 years. Questions included when ancient people transitioned from foraging to farming and whether they developed pasturelands for grazing animals. The survey also asked how confident the archaeologists were in their answers.

The 711 responses from 255 archaeologists (researchers could take the survey multiple times if they were experts in multiple regions), were weighted according to confidence and then aggregated. The results of this ArchaeoGLOBE project—which counted 112 of the respondents as co-authors—reveals that hunter-gatherer lifestyles declined globally between 10,000 and 3000 years ago as they were replaced by continuous farming, the researchers report this week in Science. By about 1000 B.C.E., all of the world’s regions that now practice farming were annually cultivating crops. [Continue reading…]