A major review of the evidence supporting the proposal that Earth has left the Holocene is published in Science today by 24 members of the Anthropocene Working Group. The group was set up by the International Commission on Stratigraphy, which makes decisions on these types of things.
The scientists, many from the global environmental change programmes, reviewed evidence from sediment and ice cores for biological and climatic signatures of human activity. They concluded that Earth has indeed left the Holocene and entered the Anthropocene, and that this should be designated an “epoch”.
The working group authors argue that the impact of humanity will be unmistakable in future sediment in several ways. Key components of the Earth system, such as the carbon cycle, water cycle and nitrogen cycle have moved beyond the Holocene envelope. New entities have entered the fossil record, for example microplastic particles – also known as microbeads or nurdles. And biodiversity has been altered. Future fossil hunters will notice that species jump from one continent to another as humans redistributed species around the globe, and many species became extinct: Earth’s biodiversity is approaching mass extinction rates.
“The stratigraphic signatures described (…) are either entirely novel with respect to those found in the Holocene and preexisting epochs or quantitatively outside the range of variation of the proposed Holocene subdivisions*,” the authors say.
One of the biggest debates around the Anthropocene has been the question of when it started. Some argue for an “early Anthropocene” near the start of the Holocene with the first agricultural revolution about 8000 years ago. Around 1610 has been proposed when the “Old World” civilisations collided with the “New World” civilisations leading to noticeable impacts on the biosphere. The Industrial Revolution is a strong contender, when greenhouse gas emissions began rising rapidly. And the final proposal is “the Great Acceleration”, with a start date often given as 16 July 1945 with the detonation of the first atomic bomb, which left a radioactive signature in the sediment.
After the Second World War population and industrialization exploded. The authors note that since around the 1950s human forcings not only grew substantially but “these signatures are currently accelerating.” They conclude, that the stratigraphic evidence supports “formalization of the Anthropocene at the epoch level, with a lower boundary (still to be formally identified) suitably placed in the mid-20th century.”
The authors admit it is still an open question on whether it is even useful to formalize the term Anthropocene, “or better to leave it as an informal, albeit solidly founded, geological time term.”
“This is a complex question, in part because, quite unlike other subdivisions of geological time, the implications of formalizing the Anthropocene reach well beyond the geological community.”
The Anthropocene brings with it two firsts. If formalized, it will be the first new epoch that has unfolded under scientific scrutiny. And it will be the first caused by human action. This may have a whole range of potential legal, political and cultural implications.
The Anthropocene Working Group meet in April in Oslo to make a formal recommendation to the commission.
Click here for the paper "The Anthropocene is functionally and stratigraphically distinct from the Holocene".