Scientists debating whether to name an entire geological period due to the human effects on the planet. Calling it ‘Anthropocene’ it could be anything from 5000-10,000 years ago to 1945 onwards.

The “evidence for the prosecution”, as Zalasiewicz puts it, is compelling. Through food production and urbanization, humans have altered more than half of the planet’s ice-free land mass, and are moving as much as an order of magnitude more rock and soil around than are natural processes. Rising carbon dioxide levels in the atmosphere are expected to make the ocean 0.3–0.4 pH points more acidic by the end of this century. That will dissolve light-coloured carbonate shells and sea-floor rocks for about 1,000 years, leaving a dark band in the sea-floor sediment that will be obvious to future geologists. A similar dark stripe identifies the Palaeocene–Eocene Thermal Maximum about 55 million years ago, when global temperatures rose by some 6 °C in 20,000 years. A similar temperature jump could happen by 2100, according to some high-emissions scenarios.

If scientists can agree in principle that a new time division is justified, they will have to settle on a geological marker for its start. Some suggest the pollen of cultivated plants, arguing that mankind’s fingerprint can be seen 5,000–10,000 years ago with the beginnings of agriculture. Others support the rise in the levels of greenhouse gases and air pollution in the latter part of the eighteenth century, as industrialization began. A third group would start with the flicker of radioactive isotopes in 1945, marking the invention of nuclear weapons.