How are geological epochs divided

The geological timescale

KanaeozoicquaternaryHolocene0,0117Post-Ice Age & Historical Time, Climate Change, Expansion of Forests; Mass extinction of the Ice Age megafauna 13,000–10,000 BC BC, partly caused by humansPleistocene2,588Primitive Age: Existence of most of today's species, extinction wave at the end of the last glacial period, especially megafauna, parallel to the rise of modern humans (Homo spp.)NeogenePliocene5,332Mastodons, gazelles, pigs, hippos, horses, tapirs, cheetahs, saber-toothed cats, foxes, raccoon dogs, bears; Origin of the pre-humans (Australopithecus spp.)Miocene23,03Alps & Rocky Mountains, large savannah areas; modern animals: wolves, cats, horses, deer, camels, proboscis; further spread of the bed covers (Angiosperms)PaleogeneOligocene33,9Emergence of many modern mammalian orders and the great apes; Land connection between Asia and Europe, here replacement of native species by Asian (rhinos)Eocene55,8Diversification of mammals: odd-toed ungulates, bats, rodents, oldest primates; Dominance of the covered ones (Angiosperms)Paleocene65,5Australia, South America & Antarctica as well as North America, Greenland & Europe connected, Africa & India isolated; Further development of mammals, worldwide distribution of birdsMesozoicchalk 145,5Giant dinosaurs, crocodiles & ammonites, lots of mammals; first flowering plants (Angiosperms, i.a. Maple, oak, walnut), grasses; Mass extinction among others the dinosaurlaw 199,6The heyday of the dinosaurs, "primeval bird" Archeopteryx, first real mammal; Heyday of Gymnosperms: Sequoias, pines, ginkgo trees, cycadsTriad 251Dinosaurs, pterosaurs, crocodiles, fin lizards, lizards, bridge and beaked lizards, turtles, ichthyosaur etc Pollen transmission by insects, cycads bloomPaleozoicPerm 299Decrease in the primeval amphibians, emergence of the Therapsids, possibly forerunners of the dinosaurs; in the end: greatest mass extinction (approx. 95% of all marine & 65% of all land animals)Carbon 359,2Giant insects, spiders, amphibian diversification, first reptiles; Ferns, scale and seal trees, bare-seeded plants (Gymnosperms): Origin of hard coal!Devon 416Age of Pisces: Panzerfishes (Placodermi), Spiny sharks (Aconthodii), Coelacanth & lungfish; first terrestrial vertebrates (Tetrapoda) & winged insects; Mass extinctionSilurian 443,7first jaw-bearing vertebrates (Gnathostomata), first bony fish (Osteichthyes), Sea scorpions; first vascular plants, original land plantsOrdovician 488,3Renewed radiation: corals, graptolites, bog animals, arm pods, cephalopods, echinoderms, sea lilies (Crinoida), jawless fish (Agnathen); in the end: mass extinctionCambrian 542"Cambrian Explosion": almost all of today's invertebrate animal phyla (including arm pods), forerunners of vertebrates; at the end: extinction wave, i.a. arthropod (Arthropoda)PrecambrianNeoproterozoic 1000Multicellular Plants and Invertebrates: Basis for Developments in Cambrian; repeated great ice agesMesoproterozoic 1600Living things with cell nuclei (Eukaryotes), in the end sexual reproduction for the first timePaleoproterozoic 2500First complex single cells with organelles, later also with a cell nucleus (Eukaryotes): first green algae and unicellular animalsNeo-Archean 2800Formation of mountainsMesoarchean 3200Cyanobacteria (stromatolites)Paleoarchean 3600Bacteria (stromatolites)Eoarchic 4000Formation of the earliest forms of organic life: Prokaryotes (simple unicellular organisms without a nucleus)Hadaikum 4600Origin and formation of the earth