Plastiglomerates: The toxic human legacy

Let’s time-travel to 3023 on Planet Earth. Fossil hunters, belonging to a more intelligent life form than us, are digging up an archaeological site near a future coast. They are spurred by the discovery of some unique rock-like structure—a mix of sand, corals and sediment rocks held together by molten plastic—hidden deep in the ground. While the discovery might seem like a fictional scene from the Indiana Jones movies, that perhaps is a legacy humans may leave behind on the planet, say scientists, thanks to the discovery of plastiglomerates.

Dubbed the new ‘rock’ of the Anthropocene—a period where humans have substantially impacted our planet—plastiglomerates are masses of rocks and plastic sediments, fused together at high temperatures either due to molten lava flow, forest fires, extremely hot weather or even campfires. Unlike rocks that are formed naturally by volcanic activities and erosion, plastiglomerates are not fully natural.

Geologists reported the first known plastiglomerates in 2014 from Hawaii's Kamilo Beach, which is infamous for the plastic debris that drifted here from the Great Pacific Garbage Patch.

The samples had a generous mix of sand, volcanic rocks, shells and plastics. Among them, a fifth of all plastiglomerates contained fishing debris like nets and buoys. Nearly a quarter of them had broken lid containers, and nearly half contained plastic ‘confetti’— small, coloured plastic pieces. Since then, plastiglomerates have been discovered on various coasts in the USA, Indonesia, Canada, Portugal and Peru. Recently, scientists reported the first plastiglomerates from India—from the beaches of the Andaman and Nicobar Islands.

Plastiglomerates, unlike other plastic debris, are heavy and sink to the bottom, possibly being preserved in rock beds. While that means the molten plastic does not turn into tiny fragments of micro and nano plastics and float on the ocean, its structure could possibly preserve it for a long, long time. How long? Some are hopeful they’d make for an exciting fossil discovery in the future. A few predict they might turn into fossil fuels. Wherever they end up, it’d be a massive footprint we’d be leaving behind, for better or worse.