History of Life on Earth Across Geologic Time

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History of Life in Terms of Evolution, Paleobiology, Paleotology & Fossil Record

Across Geological Time Eons, Eras, Periods & Epochs

Colors and times adhere standards of the World Geological Sciences (IUGS) Geological Timescale
Within table, ma = millions of years ago; ka = thousands of year ago; best viewed with 1024 pixels
The top of the table corresponds to the present, with time moving to the past down the table, including events listed within the geologic time epochs. Some time points are estimates, others are stratigraphy dates of the fossil record, despite its imperfections and gaps.


Denoting Significant Events in:
Evolution, the Fossil Record,
Paleontology and Paleobiology
Start (ma)


(65 ma to today)

(2.58 ma to present)

(11 ka to today)

  • Earth in throes of human induced mass extinction event rivaling the one at the end of the Permian; ice sheets melting & greenhouse conditions building.
  • Upon entering the post-genomic era, we find that all of our ancestors have all come out of Africa, and that we retain Neanderthals' dna in our gene pool.
  • Computers and the Internet become ubiquitous by 2000 AD.
  • Humans in some poor countries are way under fed, while many in more developed countries grow obese due to overuse of maize in processed foods.
  • Modern man radiates, Darwin lives, & science appears, offering some recourse to superstition and religion for some. Most people however are math challenged, and confuse correlation and causation, particularly the politicians.
  • Ray-finned fishes have expanded unabated since their appearance at 420 ma (except for a pause that refreshed evolution in Permian extinction) to become the dominate vertebrate group, containing half of all known species. This is fortunate for humans as fishes are high in protein while low in cholesterol.

(2.6 ma to 11.7K)

  • Last ice age from 110 ka to 12 ka
  • Homo sapien speech at ~ .075 ka.
  • Humans domestic plants and animals at ~ 13 ka.
  • Different megafauna formed on different continents disappear mostly between 10 & 40 ka, including mammoths and mastodons, saber-tooth cats, and ground sloths, possibly partly due to human migration.
  • Homo sapiens (modern humans) appear at ~ 195 ka. Probable earliest migration of humans out of Africa.
  • Homo habilis at ~ 2.3 ma, hominin Homo erectus @ ~ 1.9 ma (extinct @ ~ .1 ma), Neanderthals at ~ 250 ka.
  • Oldest chimpanzee fossils at 545 ka
(23 to 2.58 ma)

(5.3 to 2.58 ma)

  • Close Hominid human ancestors appear, including Australopithecines with bipedal locomotion ~ 4.2 ma.
  • Different megafauna appear on different continents, such as mastadons at ~ 5.3 ma, & mammoths at ~ 5 ma.
  • Climate continues cooling with deciduous & coniferous forests & grasslands replacing tropical flora.

(23 to 5.3 ma)

  • Evolved forms now appear quite modern.
  • Human (Hominini tribe) – chimp (Panini tribe) divergence - 4.9 to 7.0 ma; Sahelanthropus tchadensis, possible oldest member of Family Hominidae, Subfamily Homininae, Tribe Hominini ~ 7 ma.
  • Expanding grasslands drive evolution of herbivorous grazers and ungulates such as horses, antelopes, rhinoceros and camels, and of course their associated predators. True cats appear, including saber-toothed cats.
  • Burgeoning algae and kelp at base of food chains drives diversification of marine vertebrates and their predators such as megashark Carcharodon megalodon.
  • Marine invertebrate bivalves, cephalopods, crustaceans echinoderms, and gastropods of modern form and prolific, while brachiopods and crinoids are rarities.
(65 to 23 ma)

(34 to 23 ma)

  • Wide radiation toward more modern animals occurs: most modern bird forms and mammals have appeared.
  • Coral and carbonate reef systems grow more ecologically complex with modern looking bivalve, cephalopod, crustacean, echinoderm & gastropod invertebrates.
  • On the plains, herbivore prey and their predators evolve in the unending evolutionary battle for survival.

(56 to 34 ma)

  • End Eocene extinction event mainly affects archaic marine and aquatic forms.
  • Heavily forested Earth with its vast rainforests giving way to deciduous forests.
  • Sponges adapt to fresh water around 44 ma.
  • Appearance and proliferation of grasses drives herbivor radiation; trees thrive.
  • Many modern mammals appear, including advanced primates, camels cats, dogs, horses & rodents.
  • Insects & cartilaginous and ray-finned fishes thrive worldwide.

(66 to 56 ma)

  • Rodents and earliest primates evolve.
  • Ray-finned fishes (Actinopterygii) particularly thrive, with number of families nearly tripling over next 60 million years.
  • Flowering plants and conifers radiate throughout Paleocene & Eocene, filling ecosystems of recent plant extinctions.
  • Terrestrial mammals radiate & undergo exponential body size increases to fill ecological niches left by dinosaurs and other large reptiles.


(245 to 65 ma)

(146 to 65 ma)


  • End Cretaceous extinction event annihilates all non-avian dinosaurs and ammonites; ~ 75 % of all species, 50% of genera and 17% of families meet extinction. Majority of plant species become extinct, as do all ammanoids, most belemnite cephalopods, rudist clams, and many microorganisms.
  • Social Hymenopterans (bees) appear - the super-pollinators.
  • New dinosaurs appearing near end of Cretaceous include Triceratops (at ~ 68 ma), Tyrannosaurs at ~ 67 ma and Mosasaurs late, including the large Tylosaurus, and Mosasaurus.
  • Hadrosaurids, or duck-billed dinosaurs, appear beginning at ~ 83 ma, including Edmontosaurus at ~ 73 ma.
  • Pterosaurs start a decline toward extinction.
  • Order Crocodilia (amniote tetrapods) appears at ~ 83 ma.
  • Pachycephalosauria appears at ~ 90 ma.
  • Ammonites radiate, attaining new shapes and massive sizes up to ~ 2 meters.
  • Molluscs, sponges, bivalves all abundant and new echinoid groups appear.
  • Ichthyosaurs decline and die out at ~ 90 ma, possibly due to competition from Plesiosaurs to catch the speedier teleost fishes.
  • Modern teleost fishes proliferate and modern sharks appear.
  • Earliest snakes at 112 ma or before.
  • Eusocial hymenopteran insects appear.
  • Spinosaurus, the largest known theropod, and a fish-eater, appears at ~ 112 ma, surviving until ~ 97 ma.
  • The putative oldest marsupial ancestor to kangaroos, koalas, possums, and wombats is known from Liaoning in China at 125 ma.
  • Concensus places appearance of the first flowing plants (angiosperms or Magnoliophyta) at ~ 130 ma or earlier, as the date is equivocal. They rapidly diversify due to symbiotic coevolution with & pollination by insects. Evidence suggests angiosperm ancestors diverged from an unknown group of gymnosperms in the Triassic at 245–202 ma. The oldest putative angiosperm macrofossil is Archaefructus from Liaoning, China at 125 ma.
  • Numerous new dinosaurs appear throughout the Cretaceous, and birds diversify, sharing skies with pterosaurs.
  • A massive diversification of plankton forms occurs at base of food chain.
  • Dramatic global greenhouse conditions prevail, with near tropical conditions extending to poles.
  • Supercontinent Pangea is now broken into two smaller continents. Northern Laurasia comprises current Europe, Asia, and North America & southern Gondwana comprises current Africa, South America, Australia, India, Antarctica, and Madagascar.
(208 to 146 ma)
  • The Archaeopteryx transitional bird fossil is known from Solnhofen at 150 ma.
  • Evolution of eusocial behavior in isopteran insects (termites) and Hymenopteran (ants) forms.
  • One of the largest known dinosaurs, the sauropod Brachiosaurus dinosaur, is known from ~ 154 ma.
    Ceratopsian herbivorous, beaked dinosaurs appear at ~ 158 ma.
    Earliest eutherian placental mammal occurs at ~ 160 ma & becomes the dominant mammal clade throughout the Cenozoic.
  • Decapod crustaceans appear, including diverse shrimp, crabs and lobsters.
  • Putative earliest feathers (genus Aurornis) at ~ 160 ma from Liaoning, China.
  • First birds evolved from theropod dinosaurs appear at ~ 160 ma, initially retaining teeth & bony tails.
  • Minority claims of first angiosperms (flowering plants) at ~ 160 ma.
  • Salamanders appear at ~ 164 ma.
  • Herbivorous Ankylosauria dinosaurs, armored bulky quadrupeds with short, powerful limbs appear at ~ 167 ma.
  • Ornithopods, small, fast bipedal herbivorous dinosaurs appear at ~ 169 ma.
  • Herbivorous Stegosauria dinosaurs appaer at ~ 170 ma
  • The massive Carnosauria theropod appears at 176 ma, and disappears at 93 ma..
  • The pinophyta (Conifers) come to dominate the land in greenhouse conditions.
  • Plesiosaurs radiate in marine environments.
  • First lepidopteran insects (moths and butterflies, major pollinators) at ~ 190 ma.
  • First Ginkophyta at ~ 200 ma.
  • First pliosaur marine reptiles at ~ 200 ma.
  • Ammonoid cephalods of more highly evolved Orders Ammonitida & Lytoceratina appear.
  • Archosaurian reptiles (a group including dinosaurs, extinct crocodilian relatives, and pterosaurs) dominate terrestrial environments at start, with dinosaurs radiating to become increasingly dominant among them.
  • Sea levels rise flooding continent interiors creating warm ecosystems where marine life and plants thrived as phytoplankton proliferated and diversified.
  • Breakup of supercontinent Pangaea into Gondwana and Laurasia begins, eventually leading to Atlantic Ocean. Jurassic world begins dry, then becomes increasingly tropical.
(252 to 201 ma)
  • In extinction event at ~ 200 ma, all conodonts, some 1/2 of marine genera, 3/4 of all species went extinct, including most many archosaurs, and most therapsids and large amphibians, leaving dinosaurs meager competition on land. Ammonoids, reptiles and amphibians were highly impacted.
  • Archosaurs including dynosaurs (diapsid amniotes) replace synapsids as the dominant tetrapod group by end of Triassic.
  • Plesiosaurs (reptiles that returned to the sea) appear at ~ 204 ma and persist to 66 ma.
  • Tiny early mammals evolved from synapsids, but were relegated to a fearful, nocturnal insectivores lifestyle, though one carnivorous mammal, Repenomamus robustus, putatively fed on small dinosaurs.
  • First egg laying mammals, the monotremes, appear at ~ 210 ma.
  • Earliest lizards at ~ 220 ma based on mitochondrial phylogenetics.
  • Pterosaur flying reptiles appear at ~ 228 me & last to late Cretaceous; they are the first vertebrates to evolve powered flight.
  • The first huge, long-necked Sauropod dinosaurs appear at ~ 230 ma; these quadrupeds were the largest animals to walk the Earth and the dominant terrestrial herbivores throughout much of the Mesozoic.
  • Dermaptera insects appear at ~ 208 ma.
  • The mostly carnivorous theropods (a clade including modern birds) appear at ~ 231 ma.
  • Earth becomes green and lush with ferns, seed ferns, cycads, ginkgos, and conifers, setting the perfect stage for huge sauropod dinosaurs to come.
    Earliest small dinosaurs appear.
  • Diapsid reptiles including ichthyosaurs, placodonts, pachypleurosaurs, and nothosaurs all flourish.
  • Ichthyosaur marine reptiles appear at ~ 245 ma & will persist to 90 ma..
  • First dipteran insects (true flies) appear at ~ 245 ma, to become ubiquitous by late Triassic.
  • Putative (controversial) fossil angiosperm-like pollen at 247.2–242.0 ma.
  • First marine reptiles appear at ~ 245 ma, evolving from terrestrial ancestors soon after the end-Permian extinction and will flourish to the end of the Cretaceous.
  • Most modern groups of invertebrates re-appear during recovery in evolved forms.
  • Some crinoids evolve flexible arms for motility, predominantly as a response to predation pressure, resulting in increased prevalence.
  • First proto-frogs at ~ 250 ma.
  • Early Triassic characterized by painfully slow recovery from P-T extinction (~ 10 million years or more) owing to low anaimal & plant diversity. Surviving tetrapods take some 30 my to recover. Meager surviving reptiles became the ancestors of Mesozoic animals to come.
  • Ammonoid cephalods of Order Ceratitida appear.
  • Supercontinent Pangea straddles equator and is warm and dry, with arid interior, with flora dominated by conifers and other gymnosperms to the north, and Dicroidium seed ferns to the south.



(541 to 252 ma)

(299 to 252 ma)

  • Permian ends with the Permian-Triassic (P-T) event, known as the "Great Dying", when some 95% of all life went extinct, though plants were little impacted. All blastoids & Trilobites (except for two orders Proetida, Proetidae and Brachymetopidae), tabulate corals, euripterids, all but articulate crinoids, and many more taxa die out.
  • Cynodont therapsids first appear at ~ 260 ma, a group comprising modern mammals.
  • Continental interiors become arid, leading to loss of tropical flora, and stressing groups of tetropods.
  • The Spermatophyte (seed plants including Cycadophyta, Ginkgophyta, Pinophyta have become the predominant and large trees.
  • Earliest known tapeworm fossils (Phylum Platyhelminthes) dated to 270 ma.
  • Hemipteran insects with sucking mouthparts appear.
  • Amniote tetrapods that lay eggs diversify to become the dominant land animals, setting the stage for archosaurs, lizards, mammals, and turtles to evolve.
  • Tropical forests become increasingly dry.
  • Enormous insect diversity builds, together with that of amphibians, diapsid and synapsid tetrapods, with animals adapting to herbirvorous lifestyles.
  • Seed plants become increasingly dominant.
  • Flora of Carboniferous still abundant in early Permain.
  • Supercontinent Pangaea formed at ~ 300 ma, and a global warming phase commenses melting southern ice cap.
(359 to 299 ma)
  • Pinophyta (conifers) appear at ~ 300 ma likely descending from Cordaites, as well as Cycadophyta, and Ginkgophyta, all bearing adaptations of reduced water dependency.
  • Insect order Coleoptera (beetles) appears at ~ 318 ma.
  • Modern priapulid worms appear (may not be monophyletic with Cambrian Archaeopriapulida).
  • Insect order Odonata (dragonflies) appear, with wingspans up to 72 cm.
  • A Major radiation of winged insects occurs.
  • Reptiles finally diversify by ~ 328 ma, adapting to dryer ecosymtems.
  • Hexapods (insects and Entognathans (Collembola, Diplura and Protura) are the predominant herbivores and have grown diverse and large in size.
  • Isopod crustaceans appear at ~ 300 ma.
  • Bird - mammal split with amniotes - tetrapods that lay eggs appear at ~ 312 ma, and diverge into synapsids (reptiles that gave rise to mammals) at ~ 308 ma, and diapsids (reptile group containing dinosaurs, crocodilians, birds, lizards, and snakes).
  • First amniotic egg appears at ~ 312 ma, a paramount evolutionary step enabling critical sexual reproduction on dry land.
  • Earliest reptiles evolve at ~ 315 ma from reptile-like amphibians, but are tiny and unimportant.
  • Although in an ice age, vast dense coal forests form, comprising calamites (giant horsetails such as Asterophyllities and Annularia), lycopsids (the club mosses Lepidodendron, Lepidophloios, and Sigillaria), Marattiales (tree ferns), pteridosperms (seed ferns such as Neuropteris, Alethopteris, and Mariopteris), and cordaites (conifer-like plants). Atmospheric oxygen hits an all-time peak.
  • A dramatic radiation of insects commenses, occupying niches as herbivores, detritivores or insectivores. and insect flight evolves.
  • High diversity of marine life across brachiopods, bryozoans, echinoderms fishes, mollusks.
  • Land plants migrate with seed plants moving to drier areas and lycopods to wetter areas.
  • Sharks diversify to fill ecological space left by extinction of placoderm armored fish predators.
  • Only trilobites of Order Proetida remain.
  • Cephalopoda Subclass Coleoidea appears at ~ 330 ma, with squid-like Belemnoidea, Neocoleoidea (e.g., squids and cuttlefish) and Octopodiformes (Octopuses and vampire squids) soon represented.
  • The first pre- or proto-amniotes appear on land by ~ 345 ma; tetrapods continue diversifying.
(419 to 359 ma)
  • A protracted (20 my long) extinction event starting at 375 ma eliminated 19% of all families, 50% of all genera and 70% of all species in marine environments; brachiopods, trilobites, and reef-building organisms decimated. Five trilobite orders go extinct, Harpitida, Phacopida, Lichida, Odontopleurida, & Corynexochida, with Proetida the lone survivor. Placoderms decline dramatically to extinction. Anoxia from algal blooms precipitated by nutrient erosion of now forested land was contributing cause together with Archaeopteris forest removing too much carbon dioxide from the atmosphere, reducing greenhouse effects, and triggering an ice age.
  • Earliest tetrapods appear at ~ 360 ma, having evolved from transitional Tetrapodomorpha that evolved from the Sarcopterygii (lobe-finned fish) - that "walked ashore".
  • Ammonoid cephalopods from Order Clymeniida appear.
  • Placoderms declining dramatically toward extinction at 360 ma.
  • The first seeds appear at ~ 370 ma (the gymnosperm seed-producing plants that includes conifers, cycads, ginkgos, and gnetales).
  • Archaeopteris, considered the first tree, appears ~ 383 ma, and proliferates so prodigiously as to transform the terrestrial ecosystems. The 20 meter tall trees form a dense canopy and shed so much organic matter as to provide a rich habitat for ditrivores.
  • Ammonoid cephalods of Orders Clymeniida & Prolecanitida appear.
  • The period where insects first emerge and colonize the land is often called the arthropod gap, between 385 and 325 ma, where the fossil record is meager; nontheless, a diversity of arthropods, including spiders, mites, myriapods and collembolids likely shared a plant-based food bounty.
  • Despite trilobite families being being reduced by about 70% from the Cambrian, they again undergo adaptive change, the last period they will do so; this is no where better recorded than in the enormous diversity seen in Moroccan trilobites.
  • The vascular plants (trachaeophytes) move inland to form extensive marshes, and then upstream to form vast flood plain forests of huge trees. Lycophytes, horsetails, ferns, and progymnosperms formed forests of primitive plants with real roots and leaves, many rather tall.
  • Spiny acanthodians and armored placoderms reach peak diversity in the Devonian, with placoderms even colonizing fresh water environments.
  • Ammonoid cephalopods from Order Goniatiida appear at ~ 390 ma.
  • First undisputed insect at ~ 400 ma, Rhyniognatha hirsti, ostensibly a larval form, from the Rhynie Chert of Scotland. Similarly, the oldest hexapod is a springtail from the same locality.
  • Brachiopods reach their all-time peak diversity along with rugose corals, contributing to building of the largest reef systems to ever exist.
  • Arachnids and flightless insect are known, though fossils are scarce.
  • Class Rhyniopsida plants appear at ~ 419 ma, contributing significantly to Devonian forests.
  • Lichens are composite organisms of algae or cyanobacteria living symbiotically with fungi; the oldest fossil from the Rhynie chert dates to 410 ma, evidence that they were among the first organisms to make land fall.
  • Fossils of Aglaophyton, a nonvascular land plant from the Rhynie chert, date to 410 ma. It appears intermediate between nonvascular bryophytes and vascular plants, making it a candidate for early lan invasion.
  • The first ammonites of Order Agoniatitida (primitive ammonoid ancestral to Subclass Ammonoidea) appears at ~ 410 ma.
  • Lungfishes appear early to become prominent in fresh water.
  • Devonian is particularly noted for colonization of land by both plants and animals.
  • The first significant adaptive radiation of terrestrial life also occurred among both plants and animals.
  • Known as Age of Fishes, due to massive radiation of vertebrates with jaws, the gnathostomes, or jawed fishes.
  • Earth’s land comprises neighboring supercontinents Gondwana to the south, Siberia to the north, and the small continent of Euramerica in between. Climate is warm & glaciation absent.
(443 to 419 ma)
  • First true bony fish (Osteichthyes) appear in two class, the Sarcopterygii (lobe-finned fish) at ~ 418 ma, and the Actinopterygii (ray-finned fishes) at ~ 420 ma, setting the stage for Devonian Age of Fishes; importantly, the Sarcopterygii comprise a clade containing coelacanths, lungfish, and the tetrapods that will give rise to the first land vertebrates at ~ 360 ma.
  • First arachnid (Trigonotarbida) at ~ 420 ma.
  • Vertebrate Class Chondrichthyes, the jawed cartilaginous fish, appear at ~ 422 ma, in Subclass Elasmobranchii containing sharks, rays and skates. Subclass Holocephali appears later at ~ 416 ma in the lower Devonian.
  • Bivalve gills adapt for filter feeding.
  • Sea scorpions (Eurypterids) attain peak diverse in the Silurian and Lower Devonian, after which their diversity rapidly declines.
  • Climate warms to camparability with Ordovician and Devonian.
  • Vertebrate Class Osteostraci were the first bony, armored and jawless fish (Agnathans), that appear ~ 428 ma, and die out at the end of the Devonian. They diversify through the Silurian.
  • Lycopod vascular plants (Lycopodiophyta, containing clubmosses & scale trees) appear at ~ 428 ma.
  • Arthropleuridea subclass of herbivorous myriapod arthropods appear at ~ 428 ma, with genus Arthropleura reaching more than 2 meters, the largest land invertebrate to ever live.
  • The oldest undisputed millipede myriapod in fossil record, Pneumodesmus, at ~ 428 ma from Scotland is the first known terrestrial animal.
  • The oldest Tracheophyta (vascular plant or higher evolved plant) genus, Cooksonia, genus appears at ~ 433 ma.
  • The Acanthodii jawed fish appear shortly after the Placoderms at ~ 430 ma, making them the oldest jawed vertebrate (Chordata infraphylum Gnathostomata).
  • Minor extinction event at ~ 433 ma due to deep water anoxia resulted in loss of 1/2 of trilobite species, 80% of the conodont species, and loss of many graptolites.
  • The Class Placodermi armored fish (the earliest branch of jawed fishes, or Gnathostomata) appear at ~ 430 ma; no fossil evidence exists that they had the first vertebrate jaws. Placoderms are paraphyletic within 10 orders comprising several distinct outgroups or sister taxa to all living jawed vertebrates. Placoderms are the oldest vertebrates known to have evolved live birth. The oldest fossil from Order Antiarchi dates to the end of the Llandovery epoch at ~ 433 ma; other Placodermi group continue appearing into the later Devonian.
  • Plants and air breathing animals begin colonizing the land, though major radiations would await the Devonian.
  • Horseshoe crabs and eurypterids invade aquatic environs.
  • High sea levels and warm shallow continental margin foster a rapid recovery from end-Ordovician extinction of all manner of marine life across trilobites, cephalopods, brachiopods, corals, gastropods, bryozoa, corals, echinoderms, and more.
  • Siberia, Laurentia and Baltica all near the equator, while Gondwana drifts across the South Pole. Silurian starts with global icehouse & high latitude ice sheets. The vast Panthalassa Ocean covers most of the northern hemisphere.
(485 to 443 ma)


  • Mass extinction event in two pulses starting ~ 450 mya lasting 10 my, killing 27% of families, 57% of genera & 70% of species, only second to (P-T) extinction at end of Paleozoic in severity. Putative cause was Gondwana drift to south pole region, causing global cooling, glaciation and sea level fall, disrupting continental shelves. Broad impact to invertebrates.
  • Trilobite Order Ptychopariida disappears near end of Ordovician.
  • Class Anaspida (jawless fish) first appears at about 444 ma and has four genera, all disappearing by the end of the Silurian.
  • The first members of Echinoderm Class Echinoidea (the Echinoids) appear at ~ 450 ma, after which they lead successful lives to present day, and become widespread index fossils.
  • Class Thelodonti jawless armored fish appear at ~ 453 ma and live to the end at the Devonian extinction.
  • Stromatolites become relatively rare, as microbial mats are grazed by reef dwellers, and are increasingly relegated to environments to hostile reef dwellers.


  • Eurypterids diversify, eventually to 11 superfamilies across two suborders.
  • Putative first non-vascular land plant spores at ~ 460 ma or earlier.
  • Complex shallow water reef systems proliferate.
  • Bivavia undergoes great diversification of species.
  • The earliest enchinoderm of Class Blastoidea (Blastoids) appear in the Middle Ordovician.


  • Lower Ordovician trilobite domination of reefs gives way to a more diverse set of fauna; by then, they have evolved various morphologies for stealth and defence.
  • Oldest fossil of Phylum Bryozoa at ~ 485 ma, though it is likely they appeared much earlier in soft-bodied form.From fossil spores inference can be made that the first land plants resembled liverworts that were inextricablt linked to a wet environment due to lack of a vascular system.
  • Neglecting Echmatocrinus of the Burgess Shale, and eocrinoids that evolved from cystoids, the earliest crinoids appear in the Ordovician, afterwhich they radiated significantly.
  • The oldest Eurypterid fossils are known from the Lower Ordovician of New York. They were formidable predators for more than 200 my, until the Permian extinction. The largest known, Jaekelopterus of Devonian Germany reached 2.5 M, making it the largest known arthropod.
  • A profound bounce back from prior extinction event ensues, with more than three time the biodiversity added than during the preceding Cambrian Explosion -- this period is often called the Great Ordovician Radiation, or even, Ordovician Explosion, after its Cambrian namesake. Shallow waters promoted formation of increasingly complex reef systems.
  • The period begins hot with sea levels rising to the highest in the Paleozoic, creating new shallow environs.
  • The last trilobite order to appear, Phacopida, occurs in the fossil record at the base of the Ordovician, but its progenitor remains uncertain. Among three phacopid suborders, Phacopina appears with highly sophisticated schizochroal compound eyes with up to 700 individual lenses.
(541 to 485 ma)
  • The Cambrian – Ordovician extinction event commences at 488  and eliminates many brachiopods and conodonts, and severely reduces trilobite species.
  • Trilobites also begin specializations both for predation and defence, with many exotic morphological adaptations to come over the suceeding 300 million years before their extinction.
  • Trilobites reach their maximum diversity in terms of number of families at the end of the Cambrian.
  • Ignoring the Chengjiang Chordates, and the Conodonts, the earliest Agnathan (jawless fish) are within subclass Heterostraci of Chordata Class Pteraspidomorphi from ~ 488 ma, members of which live on to the end of the Devonian at ~ 359 ma. Importantly, they have long been candidates as ancesters to jawed vertebrates.
  • Echinoderm Subclass Asterozoa, Classes Asteroidea (starfish), and Ophiuroidea (brittle stars) first appear at ~ 488 ma.
  • The Paleoloricata appear in the upper Cambrian, and are considered as a stem group of more moderm chiton in Mollusc Subclass Polyplacophora.
  • First Nautiloids cephalopods appear at ~ 495 mya, proceeding to quickly achieve great diverty as primary predators, and remain highly diverse through the Devonian.
  • First eel-like, soft-bodied, Conodont vertebrates (Superclass Agnatha jawless fish, excluding Chengjiang Biota) appear at ~ 495 ma.
  • The most diverse Mullusc Class, Gastropoda, evolves by the late Cambrian.
Series 3
  • Land plants potentially evolve from green algae at ~ 510 ma, with some estimates earlier in Ediacaran at 630 ma.
  • Trilobite Orders Proetida and Harpetida appear, both decending from Suborder Ptychopariina of Order Ptychopariida.
  • Calcareous sponges appear.
  • Redlichiid trilobites of Suborder Redlichiina disappear.
  • Origin of Phylum Annelida is debated, though many fossils lower to middle Cambrian lagerstatten are assigned as annelids.
Series 2
  • Primitive plant forms evolved from green algae at ~ 510 ma.
  • Trilobite Orders Asaphida, descending from Ptychopariida. Trilobite Orders Lichida, and Odontopleurida appear descending from Order Redlichiida.
  • End-Botomian mass extinction at 517 ma impacted life broadly.
  • Redlichiid trilobites of Suborder Olenellina disappear before 514 ma.
  • The first animals of Phylum Mollusca in earliest Cambrian or before in the Ediacaran not yet settled; comparison often made to Ediacaran Kimberella.
  • The Chancelloriids (Order Chancelloriida) are enigmatic fossil of unknown animals fairly common in early and later Cambrian strata; an ostensibly soft body is armored with star-shaped calcareous sclerites from which radiate sharp spines.
  • Plant fossils are equivocal and limited calcareous green algae.
  • Echinoderm Subclass Homalozoa (including carpoids) appear in early Cambrian at ~ 515 ma.
  • The earliest mollusc bivavles are represented by five genera beginning at ~ 525 ma.
  • Arthropod Subphylum Crustacea, the first member of which to appear were the Malacostracan Phyllocarids, well represented in early Cambrian Lagerstatten from ~ 525 ma. Many other crustacean groups of appear during the Cambrian.
  • Other notable early Cambrian phyla appearances include Brachiopoda, Chaetognatha (525), Chordata (525), Ctenophora (520), Echinodermata, except Edrioasteroidea, Hemichordata (525), Nematoda (525), Onychophora/Lobopodia (525), and Archaeopriapulida (525).
  • Among early arthropods, trilobites especially appear in the Cambrian with highly developed visual system; this along is substantiation of development in precambrian time.
  • Hexactinellid sponges siliceous spicules appear.
  • Trilobite Orders Redlichiida (Superfamily Fallotaspidoidea) and Ptychopariida (Superfamily Ellipsocephaloidea) are the earliest trilobites to appear in the fossil record, quickly followed by Orders Agnostida and Corynexochida, all the lower Cambrian.
  • Importantly, putative early chordates Pikaia, Haikouichthys and Myllokunmingia from Chengjiang Biota at ~ 530 ma have body plans consistent with superclass Agnatha jawless fish; if so, they may be the primitive ancestors of all fishes to come, of tetrapods, and ultimately reptiles, birds and mammals.
  • The oldest cephalopod fossil, Tannuella, dates to early Cambrian (Atdababian and Botomian) at ~ 530 ma.
  • Phylum Arthropoda appears at ~ 540 ma in great diversity, as are members of Class Trilobita; many have soft bodies and many already possess mineralized exoskeletons.
  • Hard parts are found in many taxa as well as sophisticated vision systems, especially among the trilobites.
  • Cambrian Explosion begins at base of Cambrian, the putative 1st major radiation of animals spanning about 20 million years, after which most animal phyla have appeared.
  • Essentially, when macroscopic fossils appear after the base of the Cambrian, they are already abundant and dispersed, after which a rapid 20 my long radiation ensues.
  • While many animals have soft bodies, many other have shells or exoskeletons.
  • The Cambrian begins with a warming trend with tropical to temporate climates, with warm, shallow & limy continental shelf waters.
  • The sudden appearance of macroscopic fossils at the base of the Cambrian is commonly known as Darwin's Dilemma having two parts: 1) It is confounding when viewed as the fossil record beginning there, as if a creation event had occured then; and, 2) that life would evolve so abnormally fast for 20 million years. The dilemma is no more, because: 1) Clearly, the animals that appear in the early cambrian do so because of hard parts that their soft progenitors in the pre-cambrian did not possess; and, 2) The explosion was not really such fast evolution as the metaphore implies, as the burst is easily understandable in light of the known factors that would have propelled speedy adaptation by natural selection -- consider it broad scale burst in a background of puntuated equilibrium.


(1000 to 541 mya)

Ediacaran or Vendian
(635 to 541 ma)
Life and Fossils in the Precambrian: Unraveling the mysteries about the emergence and evolution of life in deep of the Precambrian poses such a challenge that there will likely always remain much uncertainty about both the biology and the timelines. Not only is the fossil record sparse, in many cases whether a body fossil, ichnofossil, microfossil or molecular fossil is even a real fossil is in dispute. Some arguments center on whether forms were created in biogenic or abiotic processes. Given that a fossil is real, there can also be numerous alternatives in its interpretation. There are many fundamental question. How did genetic encoding and the enzymes to control transcription and translation of genes to proteins arise? What came first, the Archaean or Bacterial prokaryotes, and when? How did prokaryotes merge in order for eukaryotes to arise, and when? How and when did photosynthetic metabolism emerge, and aerobic metabolism? Sections below present some potential milestones and date ranges for these key evolutionary events. Together they constitute a set of suppositions, hypotheses, and theories, for which there are alternatives to each.
  • The abrupt disappearance of Ediacaran biota prior to the appearance of early Cambrian biota leads to a postulated End-Ediacaran extinction event. A geochemical marker is consistent with anoxia as the cause. An ice age is ending, with greenhouse warming about to start.
  • Despite the paucity of fossils and their disputed status, soft-bodied progenitors of early Cambrian animals were already radiating in the pre-Cambrian, including the oldest metazoans (multicellular animals) such as diverse arthropods, trilobitamorphs, worms with notochords, poriferans, echinoderm, cnidarians, ctenophorans and others spanning the dozens of phyla that would be recognised in forthcoming Cambrian fauna.
  • The Tommotian mineralized fauna (small shelly animals) appear at ~ 550 ma, after which they globally radiate. Cloudinid (Cloudina) early metazoans possibly lived in microbial mats and where not part of the formal Ediacaran biota.
  • The Doushantuo Formation (635 to 551 ma) has a high diversity of described fossils, but no adult animals, just putative larval stages of bilateral animals that are very contencious. Other fossils are purported to be phosphatized microfossils of algae, multicellular thallophytes (seaweeds), acritarchs, ciliates, and cyanophytes, adult sponges and cnidarians (coelenterates, or tabulate corals (tetracorallians).
  • The most widely accepted theory is that the earliest fish lineage begins with primitive chordates resembling sea squirts whose larvae have fish-like qualities.
  • Some Ediacaran fossils have been assigned to Class Edrioasteroidea of Phylum Echinodermata.
  • There are numerous putative taxa represented in the Ediacaran Biota, all disputed to a greater or lessor degree that they are even fossils - but it is the best we have to work with. Different morphologies are suggestive of lichens (fungus & alga symbionts), algae, foraminiferan protists, fungi, microbial colonies, intermediates between plants and animals, sponges and molluscs. Some possess bilateral symmetry & others do not. None of the putative vendian organisms have hard or mineralized parts.
  • Sponges (Phylum Porifera) have a well respected pre-Cambrian fossil record from the Ediacaran, and before to the Crypgenian of the Proterozoic; however, phylogeny is in dispute, and sponges may not be monophyletic.
  • The oldest Phylum Cnidaria fossils are often sited as ~ 580 ma, and belonging to Class Anthozoa, the coral builders.
(850 to 635 ma)
  • Stromatolites remain in decline, as proliferating, oxygen-powered eukaryotes find microbial mats a means to a luxurious herbivorous lifestyle.
  • Sponges fossils from Australia dated at 665 ma from.
  • Multicellular sponges appear, animals with cooperating cells having different functions, rather than differentiated tissues. Molecular fossils support the appearance of Demosponge not earlier than 713 nor later than 635 ma.

(1000 to 850 ma)

  • Acritarch abundance in strata shows increase, perhaps due to radiation of eukaryotic organisms such as photosynthetic dinoflagellates or eukaryotic protists.
(1600 to 1000 mya)

(1200 to 1000 ma)

  • Supercontinent Rodinia forms at ~ 1000 ma; its breakup starting 700 ma may have contributed to environmental conditions favorable to the Cambrian Explosion.

(1400 to 1200 ma)

  • Eukaryotic radiates, displacing prokaryotes or consuming prokaryotes, and consuming ever increasing amounts of the oxygen being generated by photosynthetic organisms..
  • Colonial eukaryotic green algae flagellates fill the oceans, and are destined to evolve into vascular land plants in about a billion years.

(1600 to 1400 ma)

  • Horodyskia williamsi from the Backdoor Formation of Australia (1400 ma) as well as Glacier National Park in the US are possiblt the oldest multicellular fossils, either protists or metazoans.
  • The earliest known fungi eukarayote fossil at ~ 1430 ma.
  • Microfossils with well-preserved cell wall structure are reported in strata dated between 1500 & 1400 ma.
  • The unabating build up of atmospheric oxygen is increasingly toxic to prokaryotic bacteria, enabling their replacement by newly evolved eukaryotic forms, including photosynthetic multicellular algae.
  • Regardless of when the eukaryotic cell evolved, evidence in tilted in favor of their having evolved from Archaea rather than bacteria.
  • Chloroplasts in green algae and plants, rhodoplasts in red algae and cyanelles in the glaucophytes are considered to have arisen in separate endosymbiotic event, leading to photosynthetic eukaryotes that could join photosynthetic prokaryotes in oxygenating planet Earth.
  • A second endosymbiosis event where the symbiont was a cyanobacterium resulted in appearance of chloroplasts, the plastid organelles in plants and algae cells that are used to conduct photosynthesis. Since all eukaryotic cells have mitochondria, but not all have chloroplasts, mitochondria are thought to have evolved first.
  • Mitochondria organelles appear in eukaryotic cells as a result of endosymbiosis, where an oxygen using protobacterium is engulfed by a primitive eukaryote. It then allowed the host to use oxygen to make energy (aerobic metabolism), and thrive and outcompete non-aerobic eukaryotes in an increasingly oxygen rich world. Since all eukaryotes now have mitochondria, those without apparently went extinct.
  • The appearance of eukaryotes is second to no other evolutionary milestone since life first appeared. The oldest, undisputedly eukaryotic microfossils in the fossil record are dated at 1450 ma, which corresponds to when mitochondria and plastids evolved, can be taken as a minimum age of the eukaryotic cell. Older estimates are 1650, 1800 [Link], 2100 ma, 2200, and as far back as 2700 ma based on different evidence.
(2500 to 1600 mya)

(1800 to 1600 ma)

  • Controversial fossils from the 1650 ma Vindhyan basin in India appear as filamentous and coccoidal cyanobacteria and filamentous eukaryotic algae.
  • An abundance of putative protist eukaryotic microfossils (acritarch spherical fossils of likely algal protists) are known from several late Palaeoproterozoic to early Mesoproterozoic formations in Australia and many other worldwide localities beginning around 1800 ma.
  • Stromatolite formations reach a maximum, suggesting a peaking out of atmospheric oxygenation rate due to cyanobacteria microbial mats.

(2050 to 1800 ma)

  • Atmospheric and oceanic oxygen levels were volatile throughout the Phanerzoic, with repeating transient increases and decreases that are not well understood. Oxygen depletion occurred around 1900 ma.
(2300 to 2050 ma)

  • The oldest known potential multicellular eukaryote is Grypania spiralis, a coiled algae in 2100 ma banded iron formations in Michigan.
  • Francevillian biota fossils dated at 2100 ma are potentially those of large colonies of multicellular eukaryotic organisms.
  • Earliest known single-celled eukaryote fossils are acritarchs, which become widespread at ~ 2200 mya.
  • The Great Oxygenation Event (GOE) commenses at ~ 2300 ma, when oxygen produced photosynthetically by cyanobacteria reaches a level of triggering mass extinction of intolerant anaerobic prokaryotes.
(2500 to 2300 ma)
  • Stromatolite diversity increases throughout most of Proterozoic, at times preserving microbes.
  • As the oceans become increasingly oxygenated, atmospheric oxygen builds at a higher rate.
  • Banded iron formation accelerates at ~ 2400 mya, continues at high rate until diminishing at ~ 1800 mya as the rusting of the seas proceeds.
  • Production of oxygen by photosynthetic prokaryotes exceeds absorption in oceans leading to beginning of atmospheric oxygenation at ~ 2450 mya.


(2800 to 2500 ma)

  • The supercontinent Columbia forms around 2500 mya.
  • Stromatolites formations ubuiquitous by end of Archaean, with microbial mats of cyanobacteria producing prodigious amounts of oxygen metabolic by product.
  • Molecular fossils of steranes in Australia shales suggest eukaryotic cells appeared at 2700 ma, but this remains controversial.
  • An alternate view of stromatolites and their microfossils and molecular fossils dates oxygenation by cyanobacteria no earlier than 2700 ma; other estimates are extend to 3500 ma.
  • The rusting of the Earth/oceans still not complete, and atmospheric oxygen is basically nill.
(3200 to 2800 ma)
  • Prokaryotes dominate (Eubacteria and Archaea); their simple cell forms generating extensive stromatolite reef systems that are spreading globally to all shallow coastal shelves and shoreline
  • Acritarch fossil record begins at 3200 ma. These microfossils of diverse form are generally accepted to be fossils of eukarayotic organisms such as primitive metazoan egg cases or chlorophyta cysts, with many likely related to algae. Acritarchs density in sediments shows a pattern of crashing during glacial periods; other evidence suggests the animals were subjected to predation by protists.
  • Rusting of the Earth initially prevents atmospheric oxygen buildup until the Great Oxygenation Event at 2300 ma. Most banded iron is generated between 2400 & 1900 ma.
  • Free oxygen generation from photosynthetic prokaryotes is substantial by 3000 ma, but is rapidly absorbed from atmosphere with the rusting of the Earth and oceans. Vast banded iron formation are produced.
(3600 to 3200 ma)
  • An alternate view of stromatolites and microfossils and molecular fossils places oxygenation by cyanobacteria at 2700 ma.
  • There are dozens of formations of Archaean stromatolites starting at ~ 3500 ma (in Western Australia; these include the 3550 ma Apex Chert, 3550 ma Strelly Pool, and 3430 ma Pilbara, as well as dozens of morphotypes of putative microfossils; the biogenic origins of the microfossils and the formations have all been controversial. The majority view is that of biogenic origin by oxygen-producing prokaryotes, possibly cyanobacteria was extant around 3500 ma..
(4000 to 3600 ma)

  • The rusting of the Earth begins at around 3700 ma, as evidenced by the oldest banded iron formation.
  • Oldest evidence of life is biogenic graphite from metasedimentary rocks in Western Greenland at 3700 ma.
  • Hypothesized first appearance of life at ~ 3800 ma, comprising primitive, oxygen-producing prokaryotic cells or proto-cells in Domains Archaea or Bacteria; cell metabolism chemotrophic, anerobic or photosynthetic.
  • Start of sedimentary rock record at ~ 3800 ma.
  • At base of Eoarchaean, crust of earth has cooled, oceans formed, but atmosphere highly toxoc with miniscule oxygen.
  • Earth bombardment mostly ends, though no geochemical data to estimate when this prerequisite for life occured.
Lower Imbrian
(4100 to 4000 ma)

  • When photosynthesis evolved has been controversial, if not contentious, for some 20 years. Organic molecular fossils suggest photosynthesis by perhaps a photosynthetic proteobacterium using hydrogen sulfide as the reducing agent; purple sulfur bacteria is such an organism found in anoxic hot springs.
  • A theoretical LUCA (Last Universal Common Ancestor) appears in an RNA world, where genetic information is encoded solely by RNA that can replicate itself. This views life as protocellular, prior to emergence of DNA-based cells in the Domains of Life, the Archaea, the Bacteria and the Eucarya.
  • Heavy bombardment from space ceases at ~ 4000 ma ends, allowing cooling of mantel and condensation to form oceans.
  • Oldest known rock forms on early Earth ~ 4030 ma.
(4300 to 4100 ma)
  • Late Heavy Bombardment of Earth from space likely destroyed any ocean or atmosphere or life, except potentially deeply buried microbes.
  • Crust formation continuing through Hadean, along with orogenic processes in Earth's lithosphere (crust and uppermost mantle).
Basin Groups
(4500 to 4300 ma)
  • Ice coming from space impacts to form oceans.
  • A thin outer crust layer forms with cooling, but is contantly broken by impacts.
(4567 to 4500 ma)
  • Earth's environment extreme and unsuitable for any known life forms.
  • Moon is formed by planet-sized impact ~ 4533 ma.
  • Earth forms at ~ 4567 mya.
  • Solar system forming ~ 4600 ma, with earth imitially a molten sphere under constant vulcanism, with heavy bombardment by space objects massive to small.

l Paleontology & Fossils l Paleobiology and Geologic Timeline l
l Fossil Amber l Ammonite Fossils l Dinosaur and Reptile Fossils l Fossil Kits l
l Crinoids and Echinoderms l Fish Fossils l Fossil Dealers l Insect Fossils l Invertebrate Fossils l
l Plant Fossils l Stromatolites l Trace & Ichnofossils l Trilobite Fossils l Vertebrate Fossils l