Some ecologists are arguing that humans and alien species have been churning up ecosystems far more intensively, and for far longer, than we assume:
We like to think that most nature was pristine and largely untouched until recent times. But two major studies in recent weeks say we are deluded. In one, Erle Ellis, a geographer at the University of Maryland Baltimore County, and colleagues have calculated that at least a fifth of the land across most of the world had been transformed by humans as early as 5,000 years ago — a proportion that past studies of historical land use had assumed was only reached in the past 100 years or so.
The human footprint was huge from the day, perhaps 60,000 years ago, when we began burning grasslands and forests for hunting, according to the Ellis study. It extended further with swidden “slash-and-burn” agriculture, and became more…
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