Paleobiology with Evolution of Life across Geologic Time

Also see:
Tree of Life for Fossil Record
Geological History
"visit links within the table for more information"





Geologic Time is divided and subdivided into various categories as:
Eons are divided into Eras; Eras are divided Periods; Periods and subperiods are divided into Epochs
(Epochal subdivisions referred to as "ages" are not given in the chart). Unless otherwise noted, number denote millions of years ago.








(541 mya - present)

"The age of visible life"


Evolutionary Milestones

Cenozoic Era

(65 mya - today)


(2.6 mya - today)


(11 kya - today)
Modern man radiates, "science" appears and eventually computers and the Internet and Iphones become ubiquitous.
Plants and animals domesticated at ~ 13 kya. Mass extinction ongoing due to Man.


(2.6 mya - 11K)

A major extinction event of large mammals (megafauna), with mammoths, mastodons, saber-toothed cats, glyptodons, ground sloths, cave bears, and more disappearing.
Neandertals appear and disappear; Homo erectus and Homo sapiens appear; Homo sapien speech attained at ~ 75kya.
Stone age commences with a human extinction near miss do to continuing ice age.
Glacial cycles pressure animals south


(23 - 1.8 mya)


(5 - 1.8 mya)
Ape-like ancestors of modern humans (Hominids), the australopithecines, as well as Homo habilis appear. Land and marine animals including mammals generally modern. Cooler & drier climate reduces tropical plants as deciduous & coniferous forests as well as grasslands & savannas expand.


(23 - 5 mya)
Expansive grasslands formed giving rise to new mammal forms, especially grazing horses, rhinoceros, camels, & antelopes, & of course their predators. Many primates & 1st bipedal apes. Mastodons (megafauna) appear late in epoch.
Some 95% of plants are extant today; almost all extant bird families present by epoch end, as well as about half of modern invertebrates.
Marine vertebrates diversify; whales reaching their maximum.
In the seas, vast proliferating kelp and algae fosters new vertebrate and higher mammals (seals), marine life species & associated apex predators like megalodon sharks.


(66 - 23 mya)


(34 - 23 mya)

Evolution of more modern animals continued, particularly among mammals (1st seals & sea lions). Armadillos, predatory marsupials, sloths, carnivorous ground birds evolve in South America.
Modern looking invertebrates (eg. bivalves, cephalopods, crustaceans, echinoids & snails appear in increasingly complex carbonate and coral reef systems.
Most modern bird forms present. Grazers adapt to apex predators like the saber-toothed cat with longer legs and speed. Oreodonts & other herebivores abundant.
North America develops diverse forests of deciduous trees and conifers as well as expanded grasslands.
Begins with Grande Coupure extinction event where asian fauna or flora replaces many european species.


(56 - 34 mya)
Eocene ends with extinction event.
First grasses appear, a resource for herbovores; trees thrive.
Earth covered with forests, with rain forests in North America turning to deciduous trees over epoch.
Snakes and turtles abundant and many new avian orders arise.
Insects abundant and appear modern.
Cartilaginous and ray-finned fish thrive worldwide.
Tremendous post Mesozoic mammal diversification: most extant placental mammals appear: modern camels, cats, dogs, small dawn horses, rodents & 1st true primates; 1st whales and sea cows.


(66 - 56 mya)

Flowering plants (angiosperms begin radiation extending through the Eocene, fostered by appearance and co-evolution with bees. Small mammals radiate.

Mesozoic Era
(245 - 65 mya)


(145 - 65 mya)


(100 - 66 mya)

Ends with Cretaceous - Tertiary (K–T) extinction event. Major extinctions include non avian dinosaurs and ammonites Some 17% of families, 50% of genera and 75% of species disappaer.
Tyrannosaurus and Mosasaurs appear late.


(145 - 100 mya)

Lizards; placental animals (early mammals); Also appearing: snakes; social marsupial and primitive placental animals.
New insect forms appear and radiate, including s
ocial Hymenopterans and the Orb weaver spiders (Family Araneidae) appear.
Pterosaurs common, then decline; Archosaur reptiles and dinosaurs small to huge apex predators common on land, and Chondrichthyes and Actinopterygii fishes in the seas diversify.


(208 - 146 mya)


(163 - 145 mya)

Large theropod predators such as Allosaurus Ceratosaurus & Megalosaurus.
Archaeopteryx transitional bird fossil from Solnhofen.
Archosaurian reptiles dominate the land through Jurassic, including herbivorous sauropods (Camarasaurus, Apatosaurus, Diplodocus, Brachiosaurus).

Earliest flowering plants (angiosperms) appear at ~ 160 mya or earlier.
Other appearances include birds; crabs; frogs and salamanders
Dinosaurs radiate to dominate the land.


(174 - 163 mya)

Pangaea begins to separate into Laurasia and Gondwana & Atlantic Ocean forms.
First salamanders
Herbivorous Stegosauria & Brachiosaurus & Carnosauria theropod dinosaurs appear.
Conifers dominated the land.
Plesiosaurs became common.


(201 - 174 mya)

Appearances include Pliosaurs, birds; crabs; frogs salamanders & lepidopterans.
Breakup of Pangaea begins.
First Ginkophyta.


(252 - 201 mya)


(235 - 201 mya)

Extinction even at ~ 200 mya killed some 23% of all families, 48% of all genera (20% of marine families and 55% of marine genera) and 70% to 75% of all species went extinct.
First flowering plants.
Major extinction event: tabulate corals and conodonts disappear - ammonoids, reptiles and amphibians decimated
Appearances include: dinosaurs (early theropods); crocodiles; marine reptiles; turtles; Pterosauria and mammals; Dermaptera insects.
Major new groups of seed plants appear.


(247 - 235 mya)

First termites and flies.
Early small dinosaurs like Nyasasaurus

Diapsids reptiles steadily replace sinapsids.


(252 - 247 mya)

Radiation of planktonic organisms in lower food chain.
Ichthyosaurs & belemite cephalopods
Recovery slow from P-T extinction (~ 10 million years) due to low faunal & floral diversity. Tetrapoda would take some 30 my to recover.

Paleozoic Era

(541 - 252 mya)


(299 - 252 mya)


(259 - 252 mya)

The great dying, the Permian-Triassic (P-T) extinction event at 251 mya eradicates 95% of all life, though most plants minimally affected.
Blastoids & remaining Proetid Trilobites, & all but articulate crinoids dissapear forever.


(272 - 252 mya)

Seed plants become dominant, producing large trees.
Insect order Hemiptera.
The primitive amniotes radiate into ancestors of lizards, mammals, turtles, lizards and archosaurs.


(299 - 272 mya)
~ 10 miilion years for life to recover from P-T extinction.
First cycad seed plants.
Great insect diversity builds, along with amphibians, diapsid tetrapods, and mammal-like synapsid reptiles like Dimetrodon.
Commenses with global warming.


(359 - 299 mya)

"Age of Coal"


(323 - 299 mya)

1st Conifers near end of epoch.
Diverse and common amphibians give rise to 1st reptiles (possibly amniotic) at ~ 315 mya - reptiles become dominant tetrapods by end of epoch.
The first true spiders (Order Araneae) appear sometime before 300 mya.
Dense coal forests form, comprising scale trees, ferns, club trees, tree ferns, giant horsetails, cordaites.
Major radiation of winged insects. First beetles (Coleoptera) and dragonflies (Odonata).
Hexapod arthropods large, diverse, and the primary forest herbivores.


(359 - 323 mya)

High diversity of marine life across brachiopods, bryozoans, echinoderms fishes, mollusks, and .
Land plants divide with seed plants to drier areas and lycopods to wetter areas.
Amniotic eggs appear.
Trilobites become scarce.


(419 - 359 mya)

"Age of Fishes"


(382 - 359 mya)

Mass extinction (F-F) lasting 20 my from ~ 375 mya killed some 19% of all families, 50% of all genera and 70% of all species.
Plant seeds evolved (Gymnosperms).
Land colonized by plants and animals. Appearances include: insects; sharks; amphibians (tetrapods);nd the earliest seed plants. Extensive radiation of fishes.
Rhizodont predatory lobe-finned fishes appear at ~ 377 mya & dominate fresh water well into Pennsylvanian.


(393 - 382 mya)

Plants fundamentally recognizable as today, with roots, leaves and wood etc.


(419 - 393 mya)

First lungfish.
First unequivocal insect fossil at ~ 396 mya.
First ammonites at ~ 400 mya.


(443 - 419 mya)


(423 - 419 mya)

First insects probable.
First A
rachnids (Trigonotarbida). Definitive Age of Fishes: Lobe-finned fish, the Sarcopterygii, at ~ 418 mya. Ray finned fish (Actinopterygii) appear ~ 420 mya & Cartilaginious fish, the Chondrichthyes, appaer at ~ 422 mya.
Many primitive terrestrial predators.


(427 - 423 mya)

Vascular plants appear Cooksonia.
Eurypterids, the largest arthropods that ever lived, appear and become common marine predators.


(433 - 427 mya)

Placoderms appear at ~ 430 mya.
First millipede one of earliest terretrial animals.


(443 - 433 mya)

Acanthodii (spiny sharks) appear at ~ 430 mya.i
Supercontinent Gondwana covers equatorial Earth.


(485 - 443 mya)

"Great Ordovician Radiation"



(458 - 443 mya)


Mass extinction event from ~ 450 mya lasted 10 my, killing 27% of families, 57% of genera & 70% of species, only second to (P-T) extinction at end of Paleozoic.
Vascular plant spores.
Bryozoans appear & trilobites begin to specialize.
Stromatolites become rare & mostly replaced by complex reef systems.



(470 - 458 mya)


First non-vascular land plant spores at ~ 460 mya or earlier,
Trilobites brachiopods, molluscs cephalopods and other mollucs, crinoids and other echinoderms, graptolites, cnidarians.
Evidence of first jawed fish, the Gnathostomata at ~ 460 mya. Complex shallow water reef systems proliferate..


(485 - 470 mya)


Commences with the great Ordovician radiation (Ordovician explosion), as life recovers from the Cambrian – Ordovician extinction event (488 mya). Diversity eventually far exceeded that of the Cambrian.
Trilobite Order Phacopida appears.


(541 - 485 mya)

"Cambrian Explosion"
(497 - 485 mya)
Cambrian – Ordovician event ended the Cambrian Period, where many brachiopods and conodonts perished, and trilobites were severely reduced.
First Nautilods at ~ 495 mya.
First cephalopods & gastropods and Asterozoa (starfish & brttle stars)
Series 3
(509 - 497 mya)
Appearances include: vertebrates fish; small shelly animals mostly extinct by end of early Cambrian (End-Botomian mass extinction); conodonts; trilobites radiate repeatedly and reach their peak diversity.
Series 2
(521 - 509 mya)
Primitive plant forms evolved from green algae.
Numerous mollusc forms such as Bivalvia appear through Cambrian, especially late, though phylogeny controversial, with conjecture for affinity to Ediacaran organisms.
(541 - 521 mya)
End-Botomian mass extinction from ~ 524 - 517 mya.
Cambrian Explosion, the 1st major radiation of animals when most phyla appear. Appearance of hard parts and vision - macroscopic fossils become common.
Early chordate Haikouella, and putative fish Haikouichthys and Myllokunmingia from Chengjiang Biota @ ~ 525 mya.
Echinoderms such as Crinozoa appear, likely from Ediacaran progenitprs.
First jawless fish, the Agnatha, at ~ 530 mya.


(2500-541 mya)

(1000 - 541 mya)

Ediacaran or Vendian
(635 - 541 mya)

Extinction at end of Ediacaran.
Appearance of Tommotian mineralized Fauna (small shelly animals)at ~ 550 mya: they radiate worldwide.
Macroscopic, soft-bodied organisms radiating, the oldest metazoan (multicellular animals) - fossils known as the Ediacaran Biota, including trilobitamorphs, poriferans and other enigmatic forms.

Stromatolites diminishing further, with their microbial mats providing a rich food source for herbivorous eukaryotes.

(850 - 635 mya)

(1000 - 850 mya)

Chloroblasts arise from cyanobacteria through endosymbiosis at ~ 1000 mya.
Acritarchs radiate, becoming widespread & some perhaps eukaryotic and photosynthetic dinoflagellates or eukaryotic protists.

(1600 - 1000 mya)

(1200 - 1000 mya)

Rodinia supercontinent forms at ~ 1000 mya, setting stage - its breakup at 700 mya have played a role in the Cambrian Explosion.

(1400 - 1200 mya)

Colonial green algae flagellates cover the seas; these photosynthetic eukaryotic organisms are basal to vascular land plants to come.

(1600 - 1400 mya)

Free atmospheric oxygen build-up continues desimating some prokaryotic bacteria, but enabling replacement by newly evolved eukaryotic forms, including photosynthetic multicellular algae.

(2500 - 1600 mya)

(1800 - 1600 mya)

The "Boring Billion" years of evolutionary stasis begins.
More complex single-celled life with aerobic metabolism begin diversification.
Eukaryotic mitochondria evolve.
Approximate peak of stromatolites with cyanobacteria oxygenating the atmosphere.
Fossilized filamentous algae (eukaryote) at ~ 1700 mya.

(2050 - 1800 mya)

Banded iron formation diminishes allowing atmosphere to oxygenate rapidly, reaching ~ 15% at ~ 1800 mya.
(2300 - 2050 mya)
The oldest known potential multicellular eukaryote is Grypania spiralis, appearing as a coiled algae in 2100 mya banded iron formations in Michigan. stromatolites
Putative appearance of earliest multicellular organisms at ~ 2100 mya.
Earliest known single-celled eukaryote fossils are acritarchs, which become widespread at ~ 2100 mya.
Acritarchs are most common fossils of late Proterozoic.
Great Oxygenation Event (GOE) starts at 2300 mya, where photosynthetic oxygen production builds to point of toxicity to obligate anaerobic prokaryotes intolerant of oxygen, precipitating their mass extinction.
(2500 - 2300 mya)
Banded iron formation accelerates at ~ 2400 mya, continuing at high rate until diminishing at ~ 1800 mya -- the rusting of the seas commences.
Production of oxygen by photosynthetic prokaryotes exceeds absorption in oceans leading to beginning of atmospheric oxygenation at ~ 2450 mya.


(4000-2500 mya)

(2800 - 2500 mya)

Stromatolites widespread by end of Archaean, producing prodigious ammount of oxygen metabolic by product.
Columbia supercontinent forms at ~ 2500 mya.
Molecular fossils from Australia suggest eukaryotes appeared at ~ 2700 mya, but this is not a widely accepted view, with other estimates at ~ 3500 mya.
Atmospheric oxygen only ~ 1%.

(3200 - 2800 mya)

Prokaryotes dominate (Eubacteria and Archaea); simple cell forms generate extensive stromatolite reef systems. First acritarch microscopic fossils.
1st substantial free oxygen from photosynthetic archaea and bacteria at ~ 3000 to 2300 mya, after which free oxygen produced by these prokaryotes combined with dissolved iron in the oceans to form banded iron formations until ~ 2000 to 1300 mya -- the so-called rusting of the Earth.
Oldest life of Earth evidence that is not contested at ~ 3000 mya.

(3600 - 3200 mya)

Primitive Eukaryotes as early as ~ 3500 mya after endosymbiosis.
Oxygenic photosynthetic cyanobacteria appear ~ 3500 mya.
Oldest fossils are stromatolites: Apex Chert at 3550 mya & Strelly Pool at 3430 mya in Pilbara, Western Australia.

(4000 - 3600 mya)

First banded iron formation at ~ 3700 mya.
Oxygenic photosynthetic prokaryotic bacteria appear at ~ 3500 mya.
Putative first appearance of life
, at ~ 3800 mya & is Archaea or Bacteria, chemotrophic, anerobic, asexual, prokaryotes, fairly soon after end of earth bombardment - no consensus for this geochemical-based evidence.
Oldest sedimentary rocks ~ 3800 mya.
Earth's crust cooled by ~ 4000 mya, but atmosphere comprised volcanic gases and minimal oxygen. The 1st oceans were formed.


(4567-4000 mya)

Lower Imbrian
(4100 - 4000 mya)
Self replicating RNA molecules might have appeared as early as 4000 mya.
Late heavy bombardment from space ends at around 4000 mya, setting stage for life to appear.
Earth's oldest surviving rock from Canada dated at 4030 mya.
(4300 - 4100 mya)
Nectarian begins with so-called Late Heavy Bombardment of Earth from space.
Crust formation continuing through Hadean, as does mountain building.
Basin Groups
(4500 - 4300 mya)
Name derived from groupings of major lunar impact crators.
Water begins building in atmosphere.
As outer layer of Earth cools to thin crust, constantly disrupted by impacts.
(4567 - 4500 mya)

Earth's environment exceedingly hostile to life as we know it.
Meager geological evidence survives from this time, having been destroyed by bombardment of earth from space projectiles, including the one that putatively formed the moon.
Earth forms at ~ 4567 mya. Moon forms ~ 4533 mya due to some huge impact.
Earth essentially molten owing to volcanism and space collisions.
Solar system forming ~ 4600 mya.