of Life in
Terms of Evolution, Paleobiology, Paleotology & Fossil
Geological Time Eons, Eras, Periods & Epochs
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.
Significant Events in:
Evolution, the Fossil Record, Paleontology
ma to today)
(2.58 ma to present)
ka to today)
in throes of human induced mass extinction event
rivaling the one at the end of the Permian; ice sheets
melting & greenhouse conditions building.
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.
and the Internet become ubiquitous by 2000 AD.
in some poor countries are way under fed, while many
in more developed countries grow obese due to overuse
of maize in processed foods.
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
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.
ma to 11.7K)
ice age from 110 ka to 12 ka
sapien speech at ~ .075 ka.
domestic plants and animals at ~ 13 ka.
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.
sapiens (modern humans) appear at ~ 195 ka. Probable
earliest migration of humans out of Africa.
habilis at ~ 2.3 ma, hominin Homo erectus @ ~ 1.9
ma (extinct @ ~ .1 ma), Neanderthals at ~ 250 ka.
- Oldest chimpanzee fossils at 545 ka
to 2.58 ma)
Hominid human ancestors appear, including Australopithecines
with bipedal locomotion ~ 4.2 ma.
megafauna appear on different continents, such as
mastadons at ~ 5.3 ma, & mammoths at ~ 5 ma.
continues cooling with deciduous & coniferous
forests & grasslands replacing tropical flora.
forms now appear quite modern.
(Hominini tribe) – chimp
(Panini tribe) divergence - 4.9 to 7.0 ma; Sahelanthropus
possible oldest member of Family Hominidae, Subfamily
Homininae, Tribe Hominini ~ 7 ma.
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.
algae and kelp at base of food chains drives diversification
of marine vertebrates and their predators such as
megashark Carcharodon megalodon.
invertebrate bivalves, cephalopods, crustaceans
echinoderms, and gastropods of modern form and prolific,
while brachiopods and crinoids are rarities.
radiation toward more modern animals occurs: most
modern bird forms and mammals have appeared.
and carbonate reef systems grow more ecologically
complex with modern looking bivalve, cephalopod,
crustacean, echinoderm & gastropod invertebrates.
the plains, herbivore prey and their predators evolve
in the unending evolutionary battle for survival.
Eocene extinction event mainly affects archaic marine
and aquatic forms.
forested Earth with its vast rainforests giving way
to deciduous forests.
adapt to fresh water around 44 ma.
and proliferation of grasses drives herbivor radiation;
modern mammals appear, including advanced primates,
camels cats, dogs, horses & rodents.
- Insects & cartilaginous
and ray-finned fishes thrive worldwide.
and earliest primates evolve.
fishes (Actinopterygii) particularly thrive, with
number of families nearly tripling over next
60 million years.
plants and conifers radiate throughout Paleocene & Eocene,
filling ecosystems of recent plant extinctions.
mammals radiate & undergo exponential body size
increases to fill ecological niches left by dinosaurs
and other large reptiles.
(146 to 65 ma)
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
Hymenopterans (bees) appear - the super-pollinators.
dinosaurs appearing near end of Cretaceous include
Triceratops (at ~ 68 ma), Tyrannosaurs at ~ 67 ma
and Mosasaurs late, including the large Tylosaurus,
or duck-billed dinosaurs, appear beginning at ~ 83
ma, including Edmontosaurus at ~ 73 ma.
start a decline toward extinction.
Crocodilia (amniote tetrapods) appears at ~ 83 ma.
appears at ~ 90 ma.
radiate, attaining new shapes and massive sizes up
to ~ 2 meters.
sponges, bivalves all abundant and new echinoid groups
decline and die out at ~ 90 ma, possibly due to competition
from Plesiosaurs to catch the speedier teleost fishes.
teleost fishes proliferate and modern sharks appear.
snakes at 112 ma or before.
hymenopteran insects appear.
the largest known theropod, and a fish-eater, appears
at ~ 112 ma, surviving until ~ 97 ma.
putative oldest marsupial ancestor to kangaroos,
koalas, possums, and wombats is known from Liaoning
in China at 125 ma.
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.
new dinosaurs appear throughout the Cretaceous, and
birds diversify, sharing skies with pterosaurs.
massive diversification of plankton forms occurs
at base of food chain.
global greenhouse conditions prevail, with near tropical
conditions extending to poles.
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.
Archaeopteryx transitional bird fossil is known
from Solnhofen at 150 ma.
of eusocial behavior in isopteran insects (termites)
and Hymenopteran (ants) forms.
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.
crustaceans appear, including diverse shrimp, crabs
earliest feathers (genus Aurornis) at ~ 160 ma from
birds evolved from theropod dinosaurs appear at ~
160 ma, initially retaining teeth & bony tails.
claims of first angiosperms (flowering plants) at
~ 160 ma.
appear at ~ 164 ma.
Ankylosauria dinosaurs, armored bulky quadrupeds
with short, powerful limbs appear at ~ 167 ma.
small, fast bipedal herbivorous
dinosaurs appear at ~ 169 ma.
Stegosauria dinosaurs appaer at ~ 170 ma
massive Carnosauria theropod appears at 176 ma,
and disappears at 93 ma..
pinophyta (Conifers) come to dominate the land
in greenhouse conditions.
radiate in marine environments.
lepidopteran insects (moths and butterflies, major
pollinators) at ~ 190 ma.
Ginkophyta at ~ 200 ma.
pliosaur marine reptiles at ~ 200 ma.
cephalods of more highly evolved Orders Ammonitida & Lytoceratina
reptiles (a group including dinosaurs, extinct crocodilian
relatives, and pterosaurs) dominate terrestrial environments
at start, with dinosaurs radiating to become increasingly
dominant among them.
levels rise flooding continent interiors creating
warm ecosystems where marine life and plants thrived
as phytoplankton proliferated and diversified.
of supercontinent Pangaea into Gondwana and Laurasia
begins, eventually leading to Atlantic Ocean. Jurassic
world begins dry, then becomes increasingly tropical.
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
including dynosaurs (diapsid amniotes) replace synapsids
as the dominant tetrapod group by end of Triassic.
(reptiles that returned to the sea) appear at ~ 204
ma and persist to 66 ma.
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.
egg laying mammals, the monotremes, appear at ~ 210
lizards at ~ 220 ma based on mitochondrial phylogenetics.
flying reptiles appear at ~ 228 me & last to
late Cretaceous; they are the first vertebrates to
evolve powered flight.
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.
insects appear at ~ 208 ma.
mostly carnivorous theropods (a clade including modern
birds) appear at ~ 231 ma.
becomes green and lush with ferns, seed ferns,
cycads, ginkgos, and conifers, setting the perfect
stage for huge sauropod dinosaurs to come.
small dinosaurs appear.
reptiles including ichthyosaurs, placodonts, pachypleurosaurs,
and nothosaurs all flourish.
marine reptiles appear at ~ 245 ma & will persist
to 90 ma..
dipteran insects (true flies) appear at ~ 245 ma,
to become ubiquitous by late Triassic.
(controversial) fossil angiosperm-like pollen at
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.
modern groups of invertebrates re-appear during
recovery in evolved forms.
crinoids evolve flexible arms for motility, predominantly
as a response to predation pressure, resulting
in increased prevalence.
proto-frogs at ~ 250 ma.
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
cephalods of Order Ceratitida appear.
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.
to 252 ma)
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
therapsids first appear at ~ 260 ma, a group comprising
interiors become arid, leading to loss of tropical
flora, and stressing groups of tetropods.
Spermatophyte (seed plants including Cycadophyta,
Ginkgophyta, Pinophyta have become the predominant
and large trees.
known tapeworm fossils (Phylum Platyhelminthes)
dated to 270 ma.
insects with sucking mouthparts appear.
tetrapods that lay eggs diversify to become the
dominant land animals, setting the stage for archosaurs,
lizards, mammals, and turtles to evolve.
forests become increasingly dry.
insect diversity builds, together with that of
amphibians, diapsid and synapsid tetrapods, with
animals adapting to herbirvorous lifestyles.
plants become increasingly dominant.
of Carboniferous still abundant in early Permain.
Pangaea formed at ~ 300 ma, and a global warming
phase commenses melting southern ice cap.
to 299 ma)
(conifers) appear at ~ 300 ma likely descending from
Cordaites, as well as Cycadophyta, and Ginkgophyta,
all bearing adaptations of reduced water dependency.
order Coleoptera (beetles) appears at ~ 318 ma.
priapulid worms appear (may not be monophyletic with
order Odonata (dragonflies) appear, with wingspans
up to 72 cm.
Major radiation of winged insects occurs.
finally diversify by ~ 328 ma, adapting to dryer
(insects and Entognathans (Collembola, Diplura and
Protura) are the predominant herbivores and have
grown diverse and large in size.
crustaceans appear at ~ 300 ma.
- 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
reptiles evolve at ~ 315 ma from reptile-like amphibians,
but are tiny and unimportant.
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.
dramatic radiation of insects commenses, occupying
niches as herbivores, detritivores or insectivores.
and insect flight evolves.
diversity of marine life across brachiopods, bryozoans,
echinoderms fishes, mollusks.
plants migrate with seed plants moving to drier
areas and lycopods to wetter areas.
diversify to fill ecological space left by extinction
of placoderm armored fish predators.
trilobites of Order Proetida remain.
Subclass Coleoidea appears at ~ 330 ma, with squid-like
Belemnoidea, Neocoleoidea (e.g., squids and cuttlefish)
and Octopodiformes (Octopuses and vampire squids)
first pre- or proto-amniotes appear on land by
~ 345 ma; tetrapods continue diversifying.
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
from algal blooms precipitated by nutrient erosion
of now forested land was contributing cause together
forest removing too much carbon dioxide from the
atmosphere, reducing greenhouse effects, and triggering
an ice age.
tetrapods appear at ~ 360 ma, having evolved from
transitional Tetrapodomorpha that evolved from the
Sarcopterygii (lobe-finned fish) - that "walked
cephalopods from Order Clymeniida appear.
- Placoderms declining dramatically toward extinction at
first seeds appear at ~ 370 ma (the gymnosperm
seed-producing plants that includes conifers, cycads,
ginkgos, and gnetales).
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.
cephalods of Orders Clymeniida & Prolecanitida
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
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
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.
acanthodians and armored placoderms reach peak diversity
in the Devonian, with placoderms even colonizing
fresh water environments.
cephalopods from Order Goniatiida appear at ~ 390
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.
reach their all-time peak diversity along with rugose
corals, contributing to building of the largest reef
systems to ever exist.
and flightless insect are known, though fossils are
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.
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
first ammonites of Order Agoniatitida (primitive
ammonoid ancestral to Subclass Ammonoidea) appears
at ~ 410 ma.
appear early to become prominent in fresh water.
is particularly noted for colonization of land by
both plants and animals.
first significant adaptive radiation of terrestrial
life also occurred among both plants
as Age of Fishes, due to massive radiation of vertebrates
with jaws, the gnathostomes, or jawed fishes.
land comprises neighboring supercontinents Gondwana
to the south, Siberia to the north, and the small
continent of Euramerica in between. Climate is warm & glaciation
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
lungfish, and the tetrapods that will give rise to
the first land vertebrates at ~ 360 ma.
arachnid (Trigonotarbida) at ~ 420 ma.
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.
gills adapt for filter feeding.
scorpions (Eurypterids) attain peak diverse in the
Silurian and Lower Devonian, after which their diversity
warms to camparability with Ordovician and Devonian.
Class Osteostraci were
the first bony, armored and jawless fish
that appear ~ 428 ma, and die out at the
end of the Devonian. They diversify through
vascular plants (Lycopodiophyta, containing
clubmosses & scale
trees) appear at ~ 428 ma.
subclass of herbivorous myriapod arthropods
appear at ~ 428 ma, with genus Arthropleura
more than 2 meters, the largest
land invertebrate to ever
oldest undisputed millipede myriapod
in fossil record, Pneumodesmus, at
~ 428 ma from Scotland is the
first known terrestrial animal.
oldest Tracheophyta (vascular plant or higher evolved plant) genus, Cooksonia,
at ~ 433 ma.
Acanthodii jawed fish
appear shortly after the Placoderms at ~ 430 ma, making
them the oldest
jawed vertebrate (Chordata infraphylum
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.
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.
and air breathing animals begin colonizing
though major radiations would await the Devonian.
crabs and eurypterids invade aquatic environs.
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.
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
(485 to 443 ma)
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
Anaspida (jawless fish) first
appears at about 444 ma and has four genera, all
disappearing by the end of the Silurian.
first members of Echinoderm Class Echinoidea (the
Echinoids) appear at ~ 450 ma, after which they lead
successful lives to present day, and become widespread
Thelodonti jawless armored fish appear at ~ 453 ma
and live to the end at the Devonian extinction.
become relatively rare, as microbial mats are
grazed by reef dwellers, and are increasingly relegated
to environments to hostile reef dwellers.
diversify, eventually to 11 superfamilies across
first non-vascular land plant spores at ~ 460 ma
shallow water reef systems proliferate.
undergoes great diversification of species.
earliest enchinoderm of Class Blastoidea (Blastoids)
appear in the Middle Ordovician.
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.
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
Echmatocrinus of the Burgess Shale, and eocrinoids
that evolved from cystoids, the earliest
crinoids appear in the Ordovician, afterwhich they
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.
profound bounce back from prior extinction
event ensues, with more than three time the biodiversity
added than during the preceding Cambrian
-- this period is often called the Great
Ordovician Radiation, or even, Ordovician Explosion,
after its Cambrian namesake. Shallow waters
formation of increasingly complex reef systems.
period begins hot with sea levels rising to the highest
in the Paleozoic, creating new shallow environs.
last trilobite order to appear, Phacopida,
occurs in the fossil record at the base of the Ordovician,
but its progenitor remains uncertain. Among
phacopid suborders, Phacopina appears with
highly sophisticated schizochroal compound eyes with
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
- Trilobites reach their maximum diversity in terms
of number of families at the end of the Cambrian.
the Chengjiang Chordates,
and the Conodonts, the earliest
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
Subclass Asterozoa, Classes Asteroidea (starfish),
and Ophiuroidea (brittle stars) first appear at ~
Paleoloricata appear in the upper Cambrian, and are
considered as a stem group of more moderm chiton
in Mollusc Subclass Polyplacophora.
Nautiloids cephalopods appear at ~ 495 mya, proceeding
to quickly achieve great diverty as primary predators,
and remain highly diverse through the Devonian.
eel-like, soft-bodied, Conodont vertebrates (Superclass
Agnatha jawless fish, excluding Chengjiang
appear at ~ 495 ma.
most diverse Mullusc Class, Gastropoda, evolves by
the late Cambrian.
plants potentially evolve from green algae at ~ 510
ma, with some estimates earlier in Ediacaran at 630
Orders Proetida and Harpetida appear, both decending
from Suborder Ptychopariina of Order Ptychopariida.
- Calcareous sponges appear.
trilobites of Suborder Redlichiina disappear.
of Phylum Annelida is debated, though many fossils
lower to middle Cambrian lagerstatten are assigned
plant forms evolved from green algae at ~ 510 ma.
Orders Asaphida, descending from Ptychopariida.
Trilobite Orders Lichida, and Odontopleurida appear
descending from Order Redlichiida.
mass extinction at 517 ma impacted life broadly.
trilobites of Suborder Olenellina disappear before
first animals of Phylum Mollusca in earliest Cambrian
or before in the Ediacaran not yet settled;
often made to Ediacaran Kimberella.
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.
fossils are equivocal and limited calcareous green
Subclass Homalozoa (including carpoids) appear
in early Cambrian at ~ 515 ma.
earliest mollusc bivavles are represented by five
genera beginning at ~ 525 ma.
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.
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).
early arthropods, trilobites especially appear in the Cambrian with highly
developed visual system;
is substantiation of development in precambrian
- Hexactinellid sponges siliceous spicules appear.
- Trilobite Orders Redlichiida (Superfamily
Fallotaspidoidea) and Ptychopariida (Superfamily
earliest trilobites to appear in the fossil record,
quickly followed by Orders Agnostida and Corynexochida,
all the lower Cambrian.
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
oldest cephalopod fossil, Tannuella, dates to early
Cambrian (Atdababian and Botomian) at ~ 530 ma.
Arthropoda appears at ~ 540 ma in great diversity,
as are members of Class Trilobita; many have soft
bodies and many already possess mineralized exoskeletons.
parts are found in many taxa as well as sophisticated
vision systems, especially among the trilobites.
Explosion begins at base of Cambrian, the putative
1st major radiation of animals spanning about 20
million years, after which most animal phyla have
when macroscopic fossils appear after the base
of the Cambrian, they are already abundant and
dispersed, after which a rapid 20 my long radiation
many animals have soft bodies, many other have
shells or exoskeletons.
Cambrian begins with a warming trend with
tropical to temporate climates, with warm, shallow & limy
continental shelf waters.
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.
to 541 mya)
to 541 ma)
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?
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,
and theories, for which there are alternatives to each.
abrupt disappearance of Ediacaran biota prior to
the appearance of early Cambrian biota leads to a
extinction event. A geochemical marker is consistent
with anoxia as the cause. An ice age is ending, with
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.
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
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).
most widely accepted theory is that the earliest
fish lineage begins with primitive chordates resembling
sea squirts whose larvae have fish-like qualities.
Ediacaran fossils have been assigned to Class Edrioasteroidea
of Phylum Echinodermata.
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.
oldest Phylum Cnidaria fossils are often sited as
~ 580 ma, and belonging to Class Anthozoa, the coral
to 635 ma)
remain in decline, as proliferating, oxygen-powered
eukaryotes find microbial mats
a means to a luxurious herbivorous
fossils from Australia dated at 665 ma from.
sponges appear, animals with cooperating
cells having different functions, rather than differentiated
fossils support the appearance of Demosponge
not earlier than 713 nor later than 635 ma.
abundance in strata shows increase, perhaps due to
radiation of eukaryotic organisms such as photosynthetic
dinoflagellates or eukaryotic
to 1000 mya)
to 1000 ma)
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)
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
plants in about a billion
to 1400 ma)
williamsi from the Backdoor Formation of
Australia (1400 ma) as well as Glacier National Park
in the US are possiblt the oldest multicellular fossils,
protists or metazoans.
earliest known fungi eukarayote fossil at ~ 1430 ma.
with well-preserved cell wall structure
are reported in strata dated between 1500 & 1400
unabating build up of atmospheric oxygen is increasingly
toxic to prokaryotic bacteria, enabling their
replacement by newly evolved
eukaryotic forms, including photosynthetic multicellular
of when the eukaryotic cell evolved, evidence in tilted
in favor of their having evolved
from Archaea rather than bacteria.
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
prokaryotes in oxygenating planet Earth.
second endosymbiosis event where the symbiont was a
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
organelles appear in eukaryotic cells as a result of
an oxygen using protobacterium
is engulfed by a primitive eukaryote. It
then allowed the host to use oxygen to
and thrive and outcompete non-aerobic eukaryotes
in an increasingly oxygen rich world. Since
now have mitochondria, those without apparently
appearance of eukaryotes is second to no other evolutionary
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],
2200, and as far back as 2700 ma based
on different evidence.
to 1600 mya)
(1800 to 1600 ma)
from the 1650 ma Vindhyan basin in India appear as
filamentous and coccoidal cyanobacteria
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
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)
oldest known potential multicellular eukaryote is Grypania
spiralis, a coiled algae in 2100 ma banded iron
biota fossils dated at 2100 ma are potentially those of large colonies
multicellular eukaryotic organisms.
known single-celled eukaryote fossils are acritarchs,
which become widespread at ~ 2200
Great Oxygenation Event (GOE) commenses at ~ 2300 ma, when
oxygen produced photosynthetically by cyanobacteria
reaches a level of triggering mass extinction of
(2500 to 2300 ma)
diversity increases throughout most of Proterozoic,
at times preserving microbes.
the oceans become increasingly oxygenated, atmospheric
oxygen builds at a higher rate.
iron formation accelerates at ~ 2400 mya, continues
at high rate until diminishing at ~ 1800
mya as the rusting of the seas proceeds.
of oxygen by photosynthetic prokaryotes exceeds absorption
in oceans leading to beginning of atmospheric oxygenation at
~ 2450 mya.
(2800 to 2500 ma)
forms around 2500 mya.
formations ubuiquitous by end of Archaean, with
microbial mats of cyanobacteria producing
prodigious amounts of oxygen metabolic by
- Molecular fossils of steranes in Australia shales
suggest eukaryotic cells appeared at 2700 ma, but
this remains controversial.
alternate view of stromatolites and their microfossils
and molecular fossils dates oxygenation
by cyanobacteria no earlier than 2700 ma; other
extend to 3500 ma.
rusting of the Earth/oceans still not complete, and
atmospheric oxygen is basically nill.
(3200 to 2800 ma)
dominate (Eubacteria and Archaea); their simple
cell forms generating extensive stromatolite
reef systems that are spreading
globally to all shallow coastal shelves and shoreline
fossil record begins at 3200 ma. These microfossils
of diverse form are
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.
of the Earth initially prevents atmospheric oxygen
buildup until the Great Oxygenation
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)
alternate view of stromatolites and microfossils
and molecular fossils places oxygenation by cyanobacteria
at 2700 ma.
are dozens of formations of Archaean stromatolites starting
at ~ 3500 ma (in
Western Australia; these
include the 3550
3550 ma Strelly Pool, and 3430 ma
Pilbara, as well as dozens of morphotypes
microfossils; the biogenic origins of
the microfossils and the formations have
been controversial. The majority
view is that of biogenic origin by oxygen-producing
prokaryotes, possibly cyanobacteria was
extant around 3500 ma..
to 3600 ma)
rusting of the Earth begins at around 3700 ma, as
evidenced by the oldest banded iron formation.
evidence of life is biogenic graphite from
metasedimentary rocks in Western Greenland at 3700
first appearance of life at ~ 3800 ma, comprising
oxygen-producing prokaryotic cells or proto-cells in Domains Archaea
or Bacteria; cell metabolism chemotrophic, anerobic
of sedimentary rock record at ~ 3800 ma.
base of Eoarchaean, crust of earth has cooled, oceans
highly toxoc with miniscule oxygen.
bombardment mostly ends, though no geochemical
data to estimate when
prerequisite for life occured.
(4100 to 4000 ma)
photosynthesis evolved has been controversial,
if not contentious, for some 20 years. Organic
molecular fossils suggest photosynthesis by perhaps
a photosynthetic proteobacterium using hydrogen
as the reducing agent; purple sulfur bacteria is such
an organism found in anoxic hot springs.
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.
bombardment from space ceases at ~ 4000 ma ends,
allowing cooling of mantel and condensation to form
known rock forms on early Earth ~ 4030 ma.
(4300 to 4100 ma)
Heavy Bombardment of Earth from space likely destroyed
ocean or atmosphere or life, except potentially deeply
- Crust formation continuing through
Hadean, along with orogenic processes in Earth's
lithosphere (crust and uppermost mantle).
(4500 to 4300 ma)
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.
is formed by planet-sized impact ~ 4533 ma.
forms at ~ 4567 mya.
- Solar system forming ~ 4600
ma, with earth imitially a molten sphere under constant
heavy bombardment by space objects massive