If our species ever goes extinct, intrepid alien archeologists will judge our legacy not by our bones but from our plastic litter. According to researchers at the Scripps Institution of Oceanography, plastic is now officially in the fossil record. Their analysis of sediments suggests that plastic deposits have increased exponentially since the end of World War II, doubling every 15 years.

Stone age, iron age… plastic age?

For their study, the researchers drilled sediment core samples dating back to 1834 taken from the Santa Barbara Basin seafloor. This location is ideal for assessing plastic deposits because of the still waters and almost total absence of oxygen.

Each half a centimeter of sediment corresponds to roughly two years of history. Microplastics — which are basically any type of plastic fragment that is less than five millimeters in length — were found in all layers of the core. Most of the fragments were actually clothing fibers, though.

The quantity of microplastics increased rapidly after 1945, coinciding with the post-war boom of plastic production. By 2010, the plastic deposition turned out to be 10 times greater than it was before 1945. The post-war layers also included a greater diversity of plastics including bags, polymer particles, besides fibers.

Previously, scientists have found microplastics in the oceans, in polar ice, and even on some of the most remote islands in the world — in other words, plastic pollution is virtually everywhere. More recently, studies have also reported plastics inside human poop, raising concerns about our consumption of microplastics. According to a recent study that analyzed how much plastic Americans ingest, people gulp between 74,000 to 121,000 particles per year, depending on location, age, and sex.

These findings reinforce the notion that we’ve crossed into a new geological era, the so-called Anthropocene or ‘age of mankind.’ Not only have humans affected the fossil record through plastic pollution, we have also produced nuclear explosions which left behind chemical marks that will be visible for millions of years, and altered the atmosphere and the oceans by burning fossil fuels. Even the bones of the livestock we eat are a sign that we are having a dominant impact on the planet — thereby unleashing a clearly distinguishable and unprecedented period in Earth’s geological history.

“This study shows that our plastic production is being almost perfectly copied in our sedimentary record. Our love of plastic is actually being left behind in our fossil record,” said Scripps microplastics biologist Jennifer Brandon, who is also lead author of the new study which was published in the journal Science Advances.