Scientists have discovered a hybrid stone in Hawaii that combines melted plastic with sand, shells, coral, basalt and wood.
"Plastiglomerate" is a fusion of natural and manufactured materials through heat, possibly from campfires and lava flows, researchers say.
The discovery of plastiglomerate was published in the June issue of the journal GSA Today, published by the Geological Society of America.
Some scientists say durable plastiglomerate will likely serve as a marker for humankind in the planet’s geologic record.
"It’s not a pencil mark," said Charles E. Moore, the researcher credited with finding the rocks. "It’s an indelible human marker in the 21st century that will never go away."
Moore, who is also credited with finding the Great Pacific Garbage Patch — a vortex formed by ocean and wind currents — in 1997, said he first spotted plastiglomerate stones in 2006 at Kamilo Beach on Hawaii island’s southeastern coast. The significance of the discovery was not realized until 2012, when scientist Patricia Cocoran of Western University in Ontario heard about the stones and conducted an on-site visit with Moore at Kamilo Beach, where ocean debris including plastic from the garbage patch gyre accumulates along the shoreline.
More than 200 stones were collected, some as large as a pizza, Moore said, adding that at least one was too big to fit in the bed of a pickup truck.
While Moore said some of the plastiglomerates were formed by the heat of lava flows, Cocoran has said she feels bonfires fused the rock-plastic hybrid.
Scientists say plastiglomerates are probably found elsewhere but have yet to be reported or given a name.
This summer, Moore said, he and other researchers are planning to spend six weeks on a vessel in the garbage patch area of the Pacific, about 1,000 miles north of Hawaii, catching and analyzing fish to better understand how feeding on plastic affects them.
Scientists are also taking a look at how the ingestion of plastic could transfer harmful chemicals to fish and birds.
Moore said he suspects that feeding on plastic changes the protein synthesis in the bodies of fish.
"I don’t think that’s right," he said. "We need to lessen our footprint."
Many scientists say the planet has entered a new geological epoch, the Anthropocene, in which human activity is leaving a vast and long-lasting imprint on the natural world. Along with building materials, tools and atmospheric characteristics, plastiglomerates could be future markers of humanity’s time on Earth.
The Holocene epoch started 11,700 years ago at the end of the last ice age.
Jan Zalasiewicz, a geologist at the University of Leicester in England, told The New York Times, "Plastics and plastiglomerates might well survive as future fossils." Zalasiewicz, who was not involved in the discovery, added, "If they are buried within the strata, I don’t see why they can’t persist in some form for millions of years."
The New York Times contributed to this report.
