For about 11,700 years, Earth has been in the Holocene — the relatively warm, stable geological epoch that began at the end of the last ice age. Human civilisation developed and flourished during the Holocene's remarkably stable climate, agriculture spread across the planet, populations grew, and eventually industrial civilisation emerged. But over the past few centuries — and especially since 1950 — human activity has reached such a scale that it is now reshaping the planet itself. We have changed the atmosphere's composition, transformed the surface of half the planet, altered the chemistry of the oceans, redistributed millions of species, and started a mass extinction. These changes are not merely impressive in scale; they are now leaving a clear, layered record in sediments, ice cores, and the rocks now forming around the world. Some scientists argue that this human imprint is large enough and persistent enough to mark the beginning of a new geological epoch — the Anthropocene, the "age of humans."
The Origin of the Term
The term "Anthropocene" was popularised by the Nobel-winning atmospheric chemist Paul Crutzen in 2000. Crutzen had been working on atmospheric chemistry and ozone depletion; during a scientific meeting in Mexico, he interrupted a discussion to argue that the world was no longer in the Holocene because human activity had become so dominant. The Anthropocene as a concept resonated quickly across multiple disciplines — Earth sciences, ecology, social sciences, the humanities. By the 2010s it was being used in thousands of scientific papers and was the subject of a formal proposal to the International Commission on Stratigraphy to designate it as an official geological epoch. The biologist Eugene Stoermer had used the term informally as early as the 1980s; the Russian geologist Aleksei Pavlov had proposed a "Anthropogenic" epoch even earlier, in the 1920s. But Crutzen's 2000 use is what brought the concept into mainstream scientific and public discussion.
The Question of When It Started
If the Anthropocene is a geological epoch, it must have a start date. Several candidates have been proposed. The "early Anthropocene" hypothesis, advanced by William Ruddiman, places the start around 8,000 years ago, when early agriculture began to noticeably affect atmospheric methane and CO₂ concentrations. The "Industrial Revolution" hypothesis places it around 1750-1800, when the burning of coal began to substantially increase atmospheric CO₂. The "Great Acceleration" hypothesis places it around 1950, when essentially every measure of human impact — population, energy use, fertiliser application, vehicle ownership, plastic production, atmospheric trace gases, surface temperature, ocean acidification, biodiversity loss — began to accelerate dramatically. The 1950 date has been the most widely supported in formal stratigraphic discussions because the Great Acceleration produces a sharp, widely-distributed signal in sediments and ice cores from radioactive fallout from nuclear weapons tests.
The 2024 Decision and the Ongoing Debate
In March 2024, the International Union of Geological Sciences formally rejected a proposal to designate the Anthropocene as an official geological epoch. The decision was a narrow vote of the subcommission on Quaternary stratigraphy. The rejection does not mean the Anthropocene is unscientific — many of the underlying observations are well-established — but it means that formal stratigraphic recognition is not currently in place. The debate continues. Critics of the formal designation argued that the proposed criteria did not meet the standards used for other geological boundaries (which typically require clear, globally-distributed markers in specific reference sediments). Supporters argued that the human-driven changes to Earth systems are unambiguously of geological scale and that the existing stratigraphic framework is inadequate to capture the rapid pace of contemporary change. The Anthropocene as an informal concept remains widely used; whether it eventually becomes a formal epoch remains an open question.
The Evidence: Atmosphere
Atmospheric CO₂ has risen from a pre-industrial concentration of about 280 parts per million to over 420 parts per million today — a 50 percent increase. This is higher than at any point in the past 3 million years, and the rate of change is roughly 100 times faster than the natural changes that ended past ice ages. Methane has more than doubled. Nitrous oxide has risen by about 25 percent. The atmospheric composition is no longer the result of natural processes alone — humans are now the dominant force shaping it. Beyond greenhouse gases, the atmosphere now contains a wide range of synthetic compounds that did not exist 200 years ago: CFCs, HFCs, perfluorinated compounds, and many others. Plastics, microplastics, and combustion byproducts circulate globally through atmospheric transport.
The Evidence: Surface and Sediments
The Earth's surface has been dramatically transformed. Approximately 50 percent of the land area is now under direct human management — agriculture, urban development, plantation forestry, livestock grazing. Roughly 50,000 dams have changed the courses and sediment loads of essentially all major rivers. Concrete production has accelerated to roughly 30 billion tonnes per year — the cumulative mass of human-made concrete is now sufficient to cover the entire land surface of Earth with a few millimetres of material. Plastic production has reached 400+ million tonnes per year, with substantial fractions accumulating in soils, sediments, and the oceans. The sediments now being deposited across the world contain identifiable layers of: aluminium (unknown in nature before refining technology); fly ash from coal combustion; radioactive isotopes from nuclear weapons; persistent organic pollutants; microplastics; and chicken bones (broiler chickens — about 25 billion alive at any time — are now the most abundant terrestrial vertebrates on Earth, and their bones are accumulating in landfills and soils in numbers that will be detectable in future stratigraphy).
The Evidence: Oceans
Ocean chemistry has been substantially altered. The oceans have absorbed about 30 percent of the CO₂ humans have emitted, which has caused the average pH of surface waters to drop from about 8.2 to about 8.1 — a 30 percent increase in hydrogen ion concentration (acidity). This is the largest change in ocean chemistry in tens of millions of years and is happening faster than any natural change in the geological record. The biological consequences include reduced calcification rates in corals, mollusks, and many planktonic organisms. Ocean temperatures have risen by about 0.7°C since 1900 in surface waters and substantially in deeper waters too — the oceans have absorbed about 90 percent of the additional heat from anthropogenic global warming. Plastic pollution is found at all depths and in all ocean basins; microplastics are now ubiquitous in marine organisms, including those consumed by humans.
The Evidence: Biosphere
Human impacts on the biosphere are equally dramatic. Wild animal biomass has been substantially reduced — the global biomass of wild terrestrial mammals is now about one-sixth of pre-human levels. Domestic livestock biomass exceeds wild mammal biomass by about 14 times. Approximately one million species are currently threatened with extinction, and the current rate of extinctions is 100-1,000 times the natural background rate. The species composition of essentially every ecosystem on Earth has been altered by humans, either directly (hunting, fishing, habitat destruction) or indirectly (climate change, introduced species, pollution). Pollinator decline, coral bleaching, amphibian extinctions, large mammal declines — these are all manifestations of the same broader pattern.
The "Great Acceleration"
One of the more striking visualisations of the Anthropocene is the set of charts known as the Great Acceleration graphs, originally published by the International Geosphere-Biosphere Programme in 2004 and updated since. They show approximately 20 different indicators — population, GDP, primary energy use, fertiliser consumption, large dams, water use, paper production, transportation, telecommunications, international tourism, atmospheric CO₂ and methane, surface temperature, ocean acidification, marine fish capture, shrimp aquaculture, nitrogen flux to coastal zones, tropical forest loss, domesticated land, and terrestrial biosphere degradation. Almost every one of these indicators shows a similar pattern — relatively flat or slowly rising through 1950, then sharply rising after 1950. The simultaneous acceleration of so many different planetary indicators in the post-WWII period is one of the strongest arguments for considering 1950 the appropriate boundary for a new geological epoch.
Anthropocene Beyond Geology
The Anthropocene concept has been adopted enthusiastically far beyond stratigraphy. It has become a unifying framework for thinking about contemporary environmental problems across disciplines — climate science, ecology, environmental policy, environmental ethics, environmental humanities, history. The term encapsulates the insight that environmental problems are no longer isolated local issues but planetary-scale, interconnected phenomena requiring planetary-scale responses. Whether or not the Anthropocene becomes a formal geological epoch, it has become a powerful concept for thinking about the relationship between humans and the planetary system — including the responsibilities and possibilities that flow from the recognition that we are now a geological force.
What Comes Next
The trajectory of the Anthropocene is open. Some commentators have suggested distinguishing the current period from a hypothetical "Good Anthropocene" in which humans manage the planetary system actively and sustainably, or alternatively from a "bad Anthropocene" in which planetary boundaries are crossed and biospheric collapse follows. The choices made over the coming decades will substantially shape which trajectory the Anthropocene takes. Climate mitigation, biodiversity conservation, ocean management, resource use patterns, and population dynamics will all determine what the geological record of the Anthropocene eventually shows. The Anthropocene, in this sense, is not just an epoch we have started — it is a project we are still authoring, with the outcomes still to be determined.