Plastic Trash Becomes a New Kind of Rock
Thursday, June 5th, 2014June 5, 2014
Unusual rocks found on a beach in Hawaii may become long-lasting evidence of the impact humans are having on our planet as well as a marker for the start of a new division of geologic time. The rock is a conglomerate, a rock made up of pebbles, gravel, or the like, held together by a mineral cement. Only in this case, the cement is melted plastic from trash washed or blown ashore. The scientists involved in the rock’s identification have named it plastiglomerate. They also suspect that the new rock can be found along other coasts.
Marine researcher Charles Moore of the Algalita Marine Research Institute in Long Beach, California, found the rock on Kamilo Beach on the Big Island of Hawaii. The beach, which is heavily litered with plastic trash, has been called the dirtiest beach in the world. After hearing Moore talk about the rock, geologist Patricia Corcoran and artist Kelly Jazvac of the University of Western Ontario (UWO) in Canada decided to check out the rock for themselves. Their investigations revealed two versions of the new rock. The first, called in-situ plastiglomerate, consists of porous volcanic rocks whose many tiny holes contain melted plastic. The second, more common, kind is called clastic plastiglomerate. It consists of sand, coral, bits of wood, and other debris glued together by melted plastic.
Moore originally thought that the plastic had melted because of lava flows common to the volcanically active Big Island. However, Corcoran and Jazvac discovered that campfires, not lava, were responsible for the plastiglomerate. “It’s so polluted you couldn’t have a campfire there without burning some plastic,” Jazvac told a UWO newsletter. “The quantity is so high that if you’re living near this beach, and you want to live there, what else are you going to do with this material?”
When the scientists analyzed the rock, they found plastic from netting, ropes, and other fishing-related debris; containers and lids; tubes and pipes; and other objects. They suspect the debris came from the “Great Pacific Garbage Patch,” one of the worst regions of plastic pollution in the ocean. The Patch, which lies between California and Japan, is created by spiraling, wind-driven ocean currents carrying trash from coastal waters and other sites throughout the North Pacific.
For future geologists, the plastiglomerate may be marker for the beginning of a new geologic period. Currently, we are living in the Holocene Period, which began 11,500 years ago, with the end of the Ice Age. However, some scientists have suggested establishing a new geologic period called the Anthropocene Period to mark the time during which humans have significantly changed Earth’s natural features and ecosystems. Cocoran’s team believes that plastiglomerate, which is much denser than ordinary plastic, could become buried in the sand and, thus, become part of the rock record. “If someone came along a million years from now, and was looking at a stratigraphic [layered] section through the rock, they would be able to see this plastic along one horizon and say this was the time when humankind was using so much plastic and not disposing of it properly,” Corcoran said.
Additional World Book articles:
- Earth (Age of Earth)
- Geology
- Plastic Planet (a Special Report)