If human civilization were to be destroyed and its cities wiped off the map, there would be an easy way for future intelligent life-forms to know when the mid-20th century began: plastic.

From the 1950s to today, 8.3 billion metric tons of plastic have been produced, with around half of it made since 2004. And since plastic does not naturally degrade, the billions of tons sitting in landfills, floating in the oceans or piling up on city streets will provide a marker if later civilizations ever want to classify our era. Perhaps they will call this time on Earth the Plastocene Epoch.

A new study in Science Advances published Wednesday offered the first analysis of all mass-produced plastics ever manufactured: how much has been made, what kind and what happens to the material once it has outlived its use.

Roland Geyer, the lead author of the study, said, “My mantra is that you can’t manage what you don’t measure, and without good numbers, you don’t know if we have a real problem.”

The authors, who come from the University of California, Santa Barbara, the University of Georgia and the Sea Education Association in Woods Hole, Mass., used plastic production data from a variety of sources to make their estimates.

Their findings suggest that staggering amounts of near-eternal litter is present in the environment — the oceans, landfills and freshwater and terrestrial ecosystems — and the numbers are quite likely to increase, with 12 billion metric tons accumulating in landfills or in the environment by 2050. (One metric ton is 1.1 short tons, the measure more commonly used in the United States.)

Scientists estimate that