Geological Time Scale

The geological time scale is Earth's history divided into a series of named time intervals seperated by significant events in Earth's history. The largest defined unit of time is the supereon (not shown on this chart). This composed of eons which are then divided into periods and epochs. How are fossils dated?

EraPeriodEpochMajor eventsStart (Years)
Cenozoic Quaternary Holocene
  • The last ice age recedes, bringing with it a 400 foot rise in sea level.
  • Rise of human civilization.
  • 11,700
  • Major ice age where continental glaciers cover much of North America and Europe.
  • Pleistocene mega-fauna flourish including mammoths, mastadons, giant sloths, horses, bears, etc.
  • Evolution of anatomically modern humans. Neandertals, Homo erectus and Homo sapiens appear.
  • 2.6 Million
    Neogene Pliocene
  • Ape-like ancestors of modern humans.
  • Global climates cooled and became dryer with the onset of glaciation cycles.
  • 5.3 Million
  • Plants and animals of the Miocene were fairly modern. Mammals and birds were well-established. Whales and seals spread. The Megalodon ruled the seas.
  • Mountain building took place in western North America, Europe, and East Asia.
  • 25 Million
    Paleogene Oligocene
  • Rapid evolution and diversification of fauna, especially mammals. Major evolution and dispersal of modern types of flowering plants.
  • 33.9 Million
  • Archaic mammals flourish and continue to develop.
  • Appearance of several "modern" mammal families. Primitive whales diversify.
  • 56 Million
  • Climate tropical. modern plants appear.
  • Mammals diversify into a number of primitive lineages following the extinction of the dinosaurs. First large mammals appear.
  • Indian Subcontinent collides with Asia.
  • 66 Million
    Mesozoic Cretaceous Late
  • Many new types of dinosaurs (e.g. Tyrannosaurs, Titanosaurs, duck bills, and horned dinosaurs) evolve on land, as do modern crocodilians.
  • Flowering plants proliferate, along with new types of insects. More modern teleost fish begin to appear. Ammonites, belemnites, rudist bivalves, echinoids and sponges all common.
  • Mosasaurs and modern sharks appear in the sea.
  • Primitive birds gradually replace pterosaurs. Monotremes, marsupials and placental mammals appear.
  • Major extinction at the end of Cretaceous kills off 3/4 of plant and animals includes dinosaurs.
  • 100.5 Million
    Early 145 Million
    Jurassic Late
  • Many types of dinosaurs, such as sauropods, carnosaurs, and stegosaurs.
  • Mammals common but small. First birds and lizards. Ichthyosaurs and plesiosaurs rule the sea.
  • Breakup of super-continent Pangaea into Gondwana and Laurasia.
  • 163 Million
    Middle 174 Million
    Early 201 Million
    Triassic Late
  • First dinosaurs being to dominate the land. Icthyosaurs and nothosaurs the oceans and pterosaurs the air.
  • First mammals and crocodilia appear
  • Many large amphibians.
  • 235 Million
    Middle 247 Million
    Early 252 Million
    Paleozoic Permian Late
  • Landmasses unite into supercontinent Pangaea.
  • Mass extinction at the end of the Permain kills off 95% of all life on earth including all all trilobites, graptolites, and blastoids.
  • 259 Million
    Middle 272 Million
    Early 298 Million
    Carboniferous Pennsylvanian
  • Winged insects radiate suddenly. Amphibians common and diverse. First reptiles and coal forests (scale trees, ferns, club trees, giant horsetails, Cordaites, etc.)
  • 323 Million
  • Large primitive trees, first land vertebrates, and amphibious sea-scorpions live amid coal-forming coastal swamps.
  • Early sharks are common and quite diverse.
  • Trilobites begin their decline becoming much less diverse.
  • 358 Million
    Devonian Late
  • Land colonized by plants and animals.
  • Fish rapidly evolve become much more diverse and begin to rule the seas.
  • Corals, bryozoa, goniatites, brachiopods and trilobites very common.
  • 382 Million
    Middle 393 Million
    Early 419 Million
    Silurian Upper
  • First Vascular plants, first millipedes and arthropleurids on land.
  • First jawed fishes populate the seas.
  • Sea-scorpions reach large size. Corals, brachiopods, and crinoids all abundant.
  • Trilobites and mollusks diverse.
  • 423 Million
    Middle 433 Million
    Lower 443 Million
    Ordovician Late
  • Invertebrates diversify into many new types.
  • Early corals, articulate brachiopods , bivalves, nautiloids, trilobites, ostracods, bryozoa, many types of echinoderms (crinoids, cystoids, starfish, etc.), branched graptolites are common.
  • Conodonts (early planktonic vertebrates) appear.
  • First green plants and fungi on land. Ice age at end of period.
  • 458 Million
    Middle 470 Million
    Early 485 Million
    Cambrian Upper
  • Major diversification of life in the Cambrian Explosion. Numerous fossils; most modern animal phyla appear.
  • Appearances include: trilobites, priapulid worms, sponges, vertebrates, jawless fish, small shelly animals, conodonts, etc.
  • Supercontinent Gondwana emerges.
  • 497 Million
    Middle 509 Million
    Early 541 Million
    Vendian or Ediacaran
  • Good fossils of the first multi-celled animals. Ediacaran biota flourish worldwide in seas. Simple trace fossils of possible worm-like animals. First sponges and trilobitomorphs. Enigmatic forms include many soft-jellied creatures shaped like bags, disks, or quilts.
  • 635 Million
  • Possible "Snowball Earth" period. Fossils still rare.
  • 850 Million
  • Trace fossils of simple multi-celled eukaryotes.
  • 1 Billion
    Stenian 1.2 Billion
    Ectasian 1.4 Billion
    Calymmian 1.6 Billion
  • First complex single-celled life: protists with nuclei
  • 1.8 Billion
    Orosirian 2.05 Billion
    Rhyacian 2.3 Billion
    Siderian 2.5 Billion
    Neoarchean 2.8 Billion
  • First stromatolites (probably colonial cyanobacteria). Oldest macrofossils.
  • 3.2 Billion
  • First known oxygen-producing bacteria. Oldest definitive microfossils.
  • 3.6 Billion
  • Simple single-celled life (probably bacteria and archaea). Oldest probable microfossils.
  • 4 Billion
    Early Imbrian
  • Indirect photosynthetic evidence (e.g., kerogen) of primordial life.
  • 4.1 Billion
    Nectarian 4.3 Billion
    Basin Groups
  • Oldest known rock (4,030 Million Years Old
  • 4.5 Billion
  • Oldest known mineral, Zircon (4,404 ± 8 Million Years Ago).
  • Formation of Moon (4,533 Million Years ago), probably from giant impact.
  • Formation of Earth (4,567 to 4,570 Million Years Ago)
  • 4.57 Billion