The eon of geological time extending from the end of the Archaean, about 2500 million years ago, to the start of the present eon (see phanerozoic), about 541 million years ago. Life in the early Proterozoic was dominated by bacteria, which flourished in shallow seas and muds. They depended on a wide variety of metabolic strategies, including photosynthesis, which were crucial in determining the composition of the earth’s atmosphere and oceans. The oldest eukaryotic fossils date from after the middle Proterozoic, about 1200 million years ago. These early protists are thought to have arisen through symbiotic associations of various prokaryotes (see endosymbiont theory), probably on several independent occasions. Towards the end of this eon comes the first fossil evidence of multicellular animal life, the Ediacaran fauna, named after the Ediacara Hills in Australia but also found elsewhere. These rocks, dated to around 650 million years ago, reveal traces of soft-bodied fanlike or quiltlike creatures, perhaps unrelated to any modern forms, as well as animals resembling jellyfish and worms. The Proterozoic is divided into three eras: the Paleoproterozoic (2500–1600 mya), the Mesoproterozoic (1600–1000 mya), and the Neoproterozoic (1000–541 mya). Three periods of the Neoproterozoic are now recognized: the Tonian period (1000–720 mya), the Cryogenian period (720–635 mya), and the Ediacaran period (635–541 mya), named after the characteristic faunal assemblage.