Coming after nearly 15 years of deliberation, a ruling by geologists on Tuesday feels almost anticlimactic: Our species has not so radically altered our world as to have started a new chapter in its history, at least not yet, a scholarly panel decided.
But even if textbooks and research papers don’t feature the “Anthropocene” epoch anytime soon, earth scientists have no doubt that humans are changing the planet. In deciding whether or not to amend the geologic timeline to reflect this, they contemplated a variety of human-driven changes that will be marked in the rocks for a long time to come.
In the end, several scholars who voted on the Anthropocene question said humankind had left too many different kinds of imprints on nature, over too broad a stretch of time, to be captured neatly by a single starting point, which is what geological timekeeping requires.
Here are some of the planet-spanning changes they considered.
Nuclear fallout
A key part of the case that some scientists made for declaring the start of the Anthropocene epoch was the pulse of radioactive isotopes that hundreds of nuclear detonations scattered across the Earth in the mid-20th century. There’s zero doubt that humans are responsible for these particles, even if they end up in different places at slightly different times.
Some scholars have, however, voiced concern about whether using weapons of mass destruction to signpost humankind’s transformation of the planet would send the wrong kind of message about our time.
Biodiversity changes
Fossilized life tells scientists a lot about what Earth was like in its deep past, and that will no doubt remain the case when future researchers try to study our time. Not only are we losing species at a rapid rate, we have also upended the places where they live and thrive (or fail to thrive), both by destroying their habitats or by domesticating them for agriculture and companionship.
Shifting ground
Our civilization moves and modifies the ground beneath us in very direct ways. We flatten hills to build cities and grow crops. We gouge out the land to extract resources or bury waste. We dam up rivers, stopping them from transporting mud and earth from the continents to the seas. Worldwide, by one estimate, the total volume of sediment that humans move each year is now more than 24 times the amount supplied by rivers.
Fossil fuels
The burning of fossil fuels is adding huge amounts of carbon dioxide and methane to the atmosphere, which together are warming Earth’s surface and oceans. Already, temperatures are rapidly moving away from their relatively stable levels during the present geologic epoch, the Holocene. That’s the period that began 11,700 years ago, when the melting of the glaciers made many parts of the planet habitable to humans.
But industrial activity is also leaving another kind of enduring legacy: Ash from the combustion of coal and fuel oil is finding its way into lake beds, sediments and the seafloor.
Plastics and other pollution
Industrial ash isn’t the only kind of matter that will remain in the mineral record as a distinctive marker of our time. There’s also pesticides, plastics, heavy metals, concrete and fertilizers, not to mention trash of all kinds from landfills.