Courtesy Patricia L. CorcoranGeologists have always considered rocks to be plastic because they are often reformed, remelted, and reshaped by tectonic forces such as heat and pressure. But now, earth scientists have declared a new type of rock they're calling plastiglomerates. It's a composition of volcanic rock and actual plastic, or a clump of rock, sand, coral and seashells all held together by a mass of melted plastic derived from human debris.
Considering we humans have been generating heaps of plastic waste since the middle of the last century (and enough to wrap up our entire planet in plastic) it's no wonder some of it has managed to find its way into the rock cycle. It's only surprising that it took us this long to notice it.
Chunks of plastiglomerate were found recently at a beach in Hawaii. Patricia Corcoran, a geologist from the University of Western Ontario, and Charles Moore, captain of the research vessel Alguita discovered plastiglomerates at 21 different sites they surveyed on Kamilo Beach located on the southern tip of the Big Island of Hawaii. Their study appears in the latest issue of GSA Today.
Courtesy NASAKamilo Beach is an isolated location that, due to ocean currents and trade winds, and its location, has long been a magnet for plastic and other trash floating on the Pacific. In the distant past, native Hawaiians collected wood from Kamilo that had floated in from the Pacific Northwest to make dugout canoes. There's no easy access to the beach - it's usually void of beach-goers and takes a two hour four-wheel drive over a jagged lava field just to reach it. But each year, 15 to 20 tons of all sorts of floating plastic - from toothbrushes to water bottles to toy green army men - pile up on the rocks and sand of Kamilo. It's not the only place of course, plastic debris has been found in different areas of ocean bottom around the world. It's not surprising that some of it ends up joined with other elements to form the new rock.
Plastiglomerates are thought to have formed probably from plastic melted in beach campfires or in lava flows, which aren't unusual on the Big Island. In the distant future, as plastic gets further buried under layers of future sedimentation or lava flows, it will likely become even more incorporated, melting and re-melting under extreme heat or pressure and filling in cracks and crevasses in the country rock much like minerals such as quartz and pyrite have done in the past. Tens or hundreds of thousands of years from now, future geologists will no doubt be able to use these traces as markers for the Anthropocene era, the name gradually gaining acceptance to describe humanity's post-agricultural or industrial time on the planet.