When Moore first discovered Kamilo Beach's plastiglomerates, he hypothesized that molten lava had melted the plastic to create the new rock. However, the researchers found that lava had not flowed in that area since before plastics were first invented.
After digging further into the mystery and talking with locals, the researchers concluded that people inadvertently created the plastiglomerates after burning plastic debris, either intentionally to try to destroy the plastic or accidentally by way of campfires.
Given this origin for the beach's plastiglomerates, the team thinks the material could be present at a lot of other beaches around the world, particularly in areas where people camp or live.
"I would say that anywhere you have abundant plastic debris and humans, there will probably be plastiglomerates," Corcoran said. Additionally, other locations where there is both active volcanism and beaches polluted with plastic, such as Iceland and the Canary Islands, could have lava-produced plastiglomerates, she said.
At present, we live in the Holocene Epoch, which began nearly 12,000 years ago. In recent years, scientists have debated whether to formally identify a new geological era called the Anthropocene, which would mark the time period when human influence significantly altered Earth's physical, chemical and biological landscape. However, scientists can't agree when the Anthropocene should begin.
Whatever the case, there are several lines of evidence that highlight humankind's impact on the planet.
For instance, with the onset of the Industrial Revolution, a lot of carbon dioxide and other greenhouse gases have been pumped into the atmosphere. And even further back, the rise of agriculture some 8,000 years ago fundamentally changed land use and led to increased atmospheric carbon dioxide and methane, as evidenced from analyses of ice cores. Additionally, soil profiles from peat bogs indicate that mining activities and the combustion of leaded gasoline have resulted in increased lead concentrations over the past 300 years, the researchers noted in their study.
With plastiglomerates, scientists now have another global marker for the Anthropocene, Corcoran said. "It definitely shows how humans have interacted with Earth's biophysical system."
What's more, Corcoran and her colleagues have analyzed the clastic plastiglomerates from Kamilo Beach, and found the new material is far denser than plastic-only particles. This suggests plastiglomerates have a much greater potential to become buried and preserved in the rock record than normal plastic debris, and that future generations of scientists will be able to look into the planet's geological record and find the plastiglomerates.
"One day in the future, people can look at this material and use it as a marker horizon to see that in around 2010, humans were polluting the planet with plastic," Corcoran said. "But that's not a legacy we really want."
The researchers describe plastiglomerate in the June issue of the journal GSA Today.
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