In order to mark the profound ways in which humans have altered the planet, a panel of scientists voted this week to designate a new geologic epoch - the Anthropocene. That decision, by the 34-member Anthropocene Working Group (AWG), marks an important step towards formally defining a new slice of the geologic record - an idea that has generated intense debate within the scientific community over the past few years.

The panel plans to submit a formal proposal for the new epoch by 2021 to the International Commission on Stratigraphy, which oversees the official geologic time chart.

What is Anthropocene?

‘Anthropocene’ was coined by scientists, notably Nobel laureate Paul Crutzen and Eugene Stoermer, in 2000 to highlight how human activity has changed many facets of the Earth.

The term is a combination of anthropos, the Greek for “human”, and “-cene”, the suffix used in names of geological epochs.

An epoch is basically a vast period of geological time spanning millennia. We officially inhabit the Holocene that began roughly 11,700 years ago and was defined by a period of relative climatic stability.

Why a new geologic epoch?

Twenty-nine members of the AWG supported the Anthropocene designation and voted in favour of starting the new epoch in the mid-20th century, when a rapidly rising human population accelerated the pace of industrial production, the use of agricultural chemicals and other human activities. At the same time, the first atomic-bomb blasts littered the globe with radioactive debris that became embedded in sediments and glacial ice, becoming part of the geologic record.

“The Anthropocene works as a geological unit of time, process and strata,” said Jan Zalasiewicz, chair of the AWG and a geologist at the University of Leicester, UK, who wasn’t confident of that conclusion when the AWG began its work a decade ago. But the vote demonstrates that the group has mostly coalesced around the geological unit. “It is distinguishable. It is distinctive,” he said.

It will be the first time that the beginning of an epoch would be based on human activity and not the consequences of changes brought about by nature. For instance, the start of the Holocene epoch marks the end of the transition from the last glacial phase to a period of warming and a rise in sea level.

When will the new epoch be ratified?

The Anthropocene epoch is expected to be ratified by the International Union of Geological Sciences in a couple of years. The vote by the working group will contribute to the formalisation of the Anthropocene as a stratigraphic entity on a par with other geologic epochs.

The group will now focus on identifying a definitive geologic marker or ‘golden spike’, which is technically called a Global boundary Stratotype Section and Point (GSSP).

The group is considering 10 candidate sites from around the world, including a cave in northern Italy, corals in the Great Barrier Reef and a lake in China. Next week, many of the scientists involved will gather in Berlin to coordinate the next two years of research. They hope to identify a single site to include in their formal proposal. They must also define the type of physical evidence in the sedimentary record that represents the start of the epoch. The group is considering whether to choose the radionuclides that came from atomic-bomb detonations from 1945 until the Limited Nuclear Test Ban Treaty of 1963, said Zalasiewicz.

Once a formal proposal is made by the AWG, it will be considered by more groups of the International Commission on Stratigraphy.