Humans have made their mark on the geological record with plastiglomerates—"rocks" formed from a mix of natural debris and plastic, fused together with heat. These rocks were first described in Hawaii almost a decade ago, but they've been seen in far-flung places since then, including a remote Brazilian island in the South Atlantic. The plastiglomerates on Trinidade Island are held together by plastic that "mainly comes from fishing nets, which is very common debris on Trinidade Island’s beaches," Federal University of Parana geologist Fernanda Avelar Santos tells Reuters. "The [nets] are dragged by the marine currents and accumulate on the beach. When the temperature rises, this plastic melts and becomes embedded with the beach's natural material."
Trinidade Island, more than 700 miles from the mainland, should be pristine. A refuge for green turtles, the volcanic island's only human inhabitants are "members of the Brazilian navy, which maintains a base on the island and protects the nesting turtles," Reuters reports. Yet the plastiglomerates were found in "a permanently preserved area ... near the place green turtles lay their eggs," Santos, author of a September study on the finds, tells the outlet. "This is new and terrifying at the same time, because pollution has reached geology," she adds, backing the idea that plastiglomerates are a signal of the Anthropocene, a proposed geologic era marked by significant human impact on the planet.
Geologist Patricia Corcoran, artist Kelly Jazvac, and oceanographer Charles Moore coined the term plastiglomerates in 2014 in documenting their appearance in Hawaii. But they "proliferate across the Earth's surface," highlighting "the need to address the global plastic crisis," Corcoran and Jazvac wrote in 2020. Last August, other researchers described the first appearance of plastiglomerates in South America—specifically, on four beaches in Peru "where illegal litter burning and campfires take place." They called on others to investigate "the toxicity that new plastic formations may induce in contrast with conventional plastics, the release of secondary contaminants (e.g., microplastics, additives), and their degradation in the environment." (Read more plastic stories.)