An international group of researchers is working to define a new geological era that will more accurately describe the current state of the planet.

Called the Anthropocene era, this geological unit suggests that humans have changed the planet so significantly that a new era is required to define its present state. The team of researchers working on this project, the Anthropocene Working Group, published findings about the subject last month and represent a collaboration among scientists across the United States and Europe.

“People are changing the planet, literally,” said Tony Barnosky, a campus professor of integrative biology and the only UC Berkeley professor in the working group. “Humans are a force of nature rather than just a part of nature.”

The term “Anthropocene” grew in use from the mid-1990s to the early 2000s. In 2000, chemist and Nobel Prize winner Paul Crutzen established and popularized the term to define the current geological state of the earth.

Currently, the working group is debating when the Anthropocene era began. There are two sides of the argument, encompassing researchers who believe that the Anthropocene era started in 1945, when the first atomic bomb was deployed, and researchers who believe that the period started several thousand years ago, when humans started altering the soils.

Barnosky led a graduate seminar on the Anthropocene era, according to Allison Stegner, a graduate student of integrative biology and Barnosky’s former student. She said the seminar strove to answer questions about how to define the Anthropocene era and whether the proposed era is, in fact, an actual geological phenomenon.

“A lot of people say that we’ve had climate change and environmental change in the past, so the changes we’re seeing now are normal. That’s true to an extent,” Stegner said. “The important thing to take away is that change is normal, but we’re seeing some pretty abnormal changes.”

The development of stone tools and the domestication of cattle are among the human-induced changes that characterize the Anthropocene, according to Mark Williams, a professor of paleobiology at the University of Leicester who is a member of the Anthropocene Working Group. These changes left “a distinctive geological signal,” he said, meaning that the changes humans have caused are visible in fossil records of plants and animals and the sedimentary deposits within lakes and rivers.

“The question is whether the human-induced changes will lead to a better or worse state for the biosphere. I think the Anthropocene is wonderful in this respect, because it connects us with the 3.8 billion year story of life on Earth, an unbroken chain of biosphere evolution,” Williams said in an email. “ We are part of that chain, and it would be terribly sad if we badly damaged it.”