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.