Plastic litter on beaches is causing plastiglomerate rocks to formLiz Barney/Guardian/eyevineDiscardedSarah Gabbott and Jan Zalasiewicz (Oxford University Press)Humanity has fallen. The last people are long dead after our inadequate efforts to cut carbon emissions let global warming continue unchecked. Most animals and plants were wiped out in the sixth mass extinction to hit our planet.Millions of years have passed and the few hardy species that survived have evolved to create a novel array of endless and beautiful forms. A new intelligent species has come to dominate Earth with the help of complex machines. They are