https://www.vice.com/en_us/article/3advqv/scientists-turn-plastic-into-diamonds-in-breakthrough

More than a billion miles away from Earth, on the ice giants of Neptune and Uranus, diamonds are forever. This isn’t cosmic poetry, but a reasonable scientific conclusion: We know that under extreme pressures and high temperatures miles beneath a planet’s surface, hydrocarbons are pummeled into a crystalline bling coveted by the affianced. But on far-flung Neptune and Uranus, the Universe’s diamond-making process is a bit more curious. Since the 1970s, scientists believed that diamonds might actually rain down toward the mostly slushy planets’ rocky interiors—a diamond rain, if you will. 

In 2017, researchers in Germany and California found a way to replicate those planetary conditions, fabricating teeny tiny diamonds called nanodiamonds in the lab using polystyrene (aka Styrofoam). Five years later and they’re back at it again, this time using some good ol’ polyethylene terephthalate (PET), according to a study published on Friday in Science Advances. The research has implications not only for our understanding of space, but paves a path toward creating nanodiamonds that are used in a range of contexts out of waste plastic.