“Formally defined, sedimentary rock is rock that forms at or near the surface of the Earth in one of several ways: by the cementing together of loose clasts (fragments or grains) that had been produced by physical or chemical weathering of pre-existing rock, by the growth of shell masses or by the cementing together of shells and shell fragments, by the accumulation and subsequent alteration of organic matter derived from living organisms, or by the precipitation of minerals directly from surface-water solutions. Layers, or “beds”, of sedimentary rock are like the pages of a book, recording tales of ancient events and ancient environments on the ever-changing face of the Earth.”
– from Earth: a Portrait of a Planet (Stephen Marshak)
What if the fragments were plastic?
In 2014 a piece of sedimentary rock containing plastic was found on a beach of the Big Island of Hawaii. It consisted of plastic, volcanic rock, beach sand, seashells, and corals. The geologists who discovered the rock says it was likely formed from burning plastic in bonfires on the shore, cementing the melted plastic with the fragments around it. Heated plastic debris can also run down into already existing rock, filling cracks. They call the new rock plastiglomerate.
Leaving the cementing qualities of melted plastic aside, what if a plastic bottle or plastic toothbrush would turn up (along with shells) as fossils in limestone? Or, if the microplastics of the oceans would sink to the bottom and cement together to a kind of plastic-sandstone? We know that plastic is very resistant to decomposing, and even though the scientists don’t agree if plastic could form sedimentary rock, there is a chance that the strata that marks the anthropocene could have plastic in it.
My site is a beach, not necessarily in Hawaii, but maybe the one around the corner from my home in Blackeberg. I will imagine plastic entering the upper part of Earth’s crust from there.
Kajsa Larsson
archandphil 
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