Archaeologists in the distant future could spend their time hunting for a peculiar type of rock current day researchers are calling a “plastiglomerate.” This is the name given to clumps of volcanic rock, sand, seashells, coral, and plastic that are beginning to show up on the beaches of Hawaii. Yes, humanity is really starting to make its mark on the fossil record, as if the plastic trapped in ice wasn’t enough.
Geologists who have studied these bizarre objects speculate they are the result of plastics that have been melted in fires, which then aggregated natural materials like sand and shell debris, a bit like a synthetic form of concrete. Teams that searched the beaches of the big island of Hawaii reportedly found small plastiglomerates at 21 different sites, indicating these objects are likely to spread over time. Humans have created six billion metric tons of plastics since the 1950s, so there’s plenty of material out there to seed new plastiglomerates.
Researchers have identified fragments of toothbrushes, rope, and bottles in the plastiglomerates discovered so far. Plastiglomerates could be created through natural means, like when plastic rubbish is melted by a forest fire or volcanic lava flow. This, along with Pacific currents carrying plastic toward the island, is one of the reasons Hawaii is seeing the material in such abundance. People burning garbage are likely to contribute just as much to the formation of the plastic-infused rocks in the future, though.
So, what’s to become of these things? Are they to be the indelible marks humanity leaves in its wake? Maybe. When plastiglomerates become dense enough, they could potentially find themselves washed out to sea where they sink to the bottom. If they are covered by sediment, these plastic rocks could become part of the fossil record. Depending on the conditions, the plastic could also be re-liquified by the internal heat of the Earth, or decomposed into oil again leaving just the impression of a toothbrush or spork for future scientists to puzzle over.