Geologic Time Scale and Earth Her/History
Detailed notes
Precambrian Eon 4.5 billion – 544 million years ago
Its name means "before Cambrian." All geologic time before the beginning of the Paleozoic
era. This includes about 90% of all geologic time and spans the time from the beginning of the
earth.
Hadean Era 4500 to 3800 million years ago
The earliest subdivision of the Precambrian, spanning the time between the formation of the
Earth, about 4.5 billion years ago, and the start of the Archaean era, 3.8 billion years ago. This
interval predates the period of true geologic time since no rocks of this age are known on
Earth, with the exception of a few meteorites. Formation of the solar system and of earth.
Earth is in a molten state. Earth bombarded by planetoids. Formation of the crust. Primal
ocean starts to form with organic amino acids. No life forms in the fossil record.
Archaean Era 3800 to 2500 million years ago
Its name means "ancient." The middle era of Precambrian time, spanning the period between
3.8 and 2.5 billion years ago. There is a permanent crust similar to the structure we see today.
Canadian Shield forms. First signs of erosion as sediment begin to accumulate in the oceans.
Life appeared on Earth during the Archaean, as indicated by the appearance of fossil bacteria
(cyannobacteria or blue-green algae) in rocks thought to be about 3.5 billion years old.
Prokaryotes, single-celled micro-organisms with no distinct organs, are present.
Proterozoic Era 2.5 billion – 544 million
Its name means "early life." The final era of the Precambrian Eon, spanning the time between
2.5 billion and 544 million years ago. Fossils of both primitive single celled (prokaryotes) and
more advanced multi-cellular organisms (Eukaryotes) begin to appear in abundance in rocks
from this era.
Sturtian Period 800 million – 650 million
Very little is known about this time. AKA: Cryogenian Period (from Greek cryos "ice" and
genesis "birth") is the second geologic period of the Neoproterozoic Era, followed by the
Ediacaran Period. The Cryogenian includes the Sturtian and Marinoan (formerly considered
together as the Varanger) glaciations, and lasted from 800 Ma (million years ago, boundary
defined chronometrically) to approximately 650 Ma.
The name is derived from the glacial deposits characteristic of the period, indicating that at
this time, the Earth suffered the most severe ice ages in its history, with glaciers extending to
the equator, in a series of rhythmical pulses. These glaciations are represented by tillite
deposits in Congo, Sahara, and Oman, in Australia and in China, and in North America,
Ireland, Scotland, and Norway, and many other places around the world. It is generally
considered to be divisible into at least two major worldwide glaciations. The tillite deposits
occur also in places which were at low latitudes during the Cryogenian, a phenomenon
which led to the hypothesis of the deeply-frozen planetary oceans called "Snowball Earth".
The population of acritarchs (Most acritarchs are surely remains of single celled lifeforms)
crashed during this glaciation and it is claimed that oxygen levels in the atmosphere
increased after the glaciation. There are a number of enigmatic features about this glaciation,
including indications of glaciation at very low latitudes and the presence of limestones -sediments that are normally warm water above and below and intermixed with glacial
deposits.
Paleomagnetism seems to show very high continental drift rates, leading some geologists to
question whether some of the phenomena might be due to magnetic pole wandering rather
than plate motion and low latitude glaciation. Basically, a very lopsided distribution of
continental crust causes the Earth's daily rotation to produce angular momentum, which
would cause the Earth to rotate (while its daily rotation axis stays in the same direction) until
the aggregation of continents is on the equator; this causes apparent continental drift that is
much faster than average rates.
Vendian Period 650 million - 544 million years ago (AKA: Ediacaran)
The latest period of the Proterozoic era, spanning the time between 650 and 544 million years
ago. Sometimes referred to as the Ediacaran period, the Vendian is distinguished by fossils
representing a characteristic collection of complex soft-bodied organisms found at several
localities around the world. Mounds of blue-green algae form structures called stromatolites
are considered to be the first fossils. Photosynthesis creates oxygen in the atmosphere which
kills off many of the early living organisms. Examples of these early life forms are present in
water near volcanic vents. Some simple worm-like fossils. First cnidarians (Greek for
“stinging nettle”), which are animals armed with stinging cells called nematocysts. Precursors
to first arthropods (“jointed leg”). Some sponges also present.
Phanerozoic Eon 544 million years ago - present
Means “Revealed Life”. Though it only represents about 10% of earth her/history it is
arguably the most interesting with virtually all life found during this time.
Paleozoic Era 544 million – 248 million
The word Paleozoic is from Greek and means "ancient life." An era of geologic time, from the
end of the Precambrian to the beginning of the Mesozoic, spanning the time between 544 and
248 million years ago. Fossil record shows first shellfish, insects, plants, fish, spiders,
amphibians, and reptiles.
Cambrian Period 544 million – 505 million
It is named after Cambria, the Roman name for Wales, where rocks of this age were first
studied. The earliest period of the Paleozoic era, spanning the time between 544 and 505
million years ago. Major formation of sedimentary rock. Continents are flooded with shallow
seas. Mild climate. “North America” is tropical. Originally thought to be the first ‘explosion’
of life but has since been adjusted. Shelled (calcium carbonate) organisms in oceans. Every
phylum of invertebrate is represented in fossil record. Trilobites abundant. First active
predators/ hunters. Some brachiopods (“long foot”). Simple echinoderms (“spiny skin”),
which are ancestors of starfish. Possibly some early crinoids or sea lilies. A few simple jawless
vertebrates like lamprey. Early sponges called archaeocyathids present; their descendants
may have been the first reef-builders. Mass extinctions including oldest trilobites.
AKA: “Age of Marine Invertebrates” due to tremendous diversity of organisms.
Ordovician Period 505 million – 440 million
It is named after a Celtic tribe called the Ordovices. The second earliest period of the
Paleozoic era, spanning the time between 505 and 440 million years ago. North America,
Europe and Africa colliding forming first highlands. Seas over North America at their
greatest extent. Rocks are mostly sedimentary. Super-continent called Gondwana in southern
hemisphere shifts toward south pole and much of it was submerged under shallow seas. In
the Late Ordovician massive glaciers dropped sea levels. Mature marine ecosystems develop
with some deep-water life. Graptolites- whose fossils look like saw blades. Fish with
notocords (early backbones) present. Jawless fish and other sea life widespread. Some plant
spores have been found suggesting primitive land plants may be in existence. Mass extinction
of 60% of all marine invertebrate genera and 25% of all families become extinct. Possible
reasons for extinction event are the cooling of the ocean and/or oxygen depletion.
Silurian Period 440 million – 417 million
It is named after a Celtic tribe called the Silures. A period of the Paleozoic, spanning the time
between 440 and 410 million years ago. Earth continues its mild climate as global temps
stabilize. Sea levels rise to previous levels. Mountains forming in Europe. Most of the world’s
salt (halite) deposits occur at this time. Earliest land plants. Extensive coral reefs present.
Jawless fish spread rapidly throughout fossil record. First fish with jaws as well as the first
sharks. Crinoids (sea lilies) abundant. Brachiopods widespread. Graptolites, conodonts,
corals, stromatoporoids and mollusks common. Land being invaded by arthropods (‘jointed
leg”) like relatives of spiders (arachnids) and centipedes. Earliest vascular plants (plants with
xylem and phloem; ferns) found in southern hemisphere; Most common plants belong to
genus Cooksonia; Controversial Baragwanathia (type of advanced vascular plant called a
lycophyte) found in Australia. Modern algae and fungus (ascomycete fossils).
Devonian Period 417 million – 360 million
A period of the Paleozoic era, spanning the time between 410 and 360 million years ago. It is
named after Devonshire, England, where rocks of this age were first studied. Extensive
volcanism in the eastern United States and Canada. Continents are becoming drier. Europe
and North America colliding near equator- orogeny continues. South Pole located in Central
Africa as South America, Africa, Antarctica, India, and Australia dominate southern
hemisphere. Fish are dominant life form- armored fish (ostracoderms), placoderms of huge
size, lungfish, Dunklosteous. First lobe-finned fish (sarcoterygiians) First land animals
develop near the end of Devonian; first amphibians. Brachiopods, echinoderms, corals
flourish. Psilotophyta (giant plants) present in southern hemisphere; Archaeopteris is an
example. Also evidence of first seed plants (spermatophytes), which are very modern-type
plants. Oldest known vascular plants found now in northern hemisphere are only one meter
tall. Brachiopods (arm- foot) are at their most diverse. Two major groups of animals colonize
land at end of Devonian: tetrapods (four legged) which are the first vertebrates and closely
related to lungfish and amphibians; and wingless insects and earliest true arachnids. AKA:
“Age of Fishes”.
Carboniferous Period 360 million – 286 million
The term ‘Carboniferous’ comes from England and refers to the large coal deposits there. A
period of time in the Paleozoic era that includes the Mississippian (Lower Carboniferus) and
the Pennsylvanian (upper Carboniferous) periods and extended from 354 to 290 million years
ago. In the United States the separation distinguishes between the mostly limestone
Mississippian and coal-bearing Pennsylvanian. The earth’s climate is still warm. Great coal
swamps cover much of lowlands on earth. Orogeny in eastern US (Appalchians), Texas,
Colorado, Britain (Hercynian Mountains), Eastern Europe/ Siberia (Ural Mountains).
Laurussia (Europe & North America) collides with Godwanaland (Africa & South America).
Though two massive ice sheets cover the South Pole, there is a decrease in seasonal variation
of temperatures. The milder climates caused the decrease of lycopods (tree-like plants) and
giant insects and the increase of tree ferns. Amphibians reach greatest number and diversity.
First reptiles appear in the late Carboniferous. This is perhaps the greatest ‘innovation’ of this
period- an Amniote egg. This is the design allowed tetrapods to lay eggs away from water- a
first in the fossil record in response to more arid conditions. Earliest amniote fossil was lizardlike Hylonomus. Other tetrapods include Amphibiamus (type of Temnospondyl),
Anthracosaurs, followed by Diapsids (most reptiles except turtles; dinosaurs and even birds
belong to this group), Synapsids (precursors to mammals, including Dimetrodon) Increase in
the diversity of insects; insects are huge. First land snails. Sharks are abundant. Great forests
of ferns, gymnosperms, horsetails. Sphenopsids (like today’s so-called Horse Tails or
Equisetum) become more prevalent. Continents are uplifted providing more terrestrial
environments but flooded areas on the continents host bryozoans (“Moss Animals”). Sea floor
dominated by brachiopods, foraminifers (single-celled protests). The Kingdom “Protista” is
one of the four kingdoms including animals, plants, and fungi. Freshwater clams appear.
Heavily armored fish from Devonian extinct. AKA: “Age of Amphibians”
Mississippian Epoch 360 million – 325 million
A period of the Paleozoic era, spanning the time between 360 and 325 million years ago. It is
named after the Mississippi River valley, which contains good exposures of rocks of this age.
Coal- forming swamps.
Pennsylvanian Epoch 325 million – 286 million
A period of the Paleozoic era, spanning the time between 325 and 286 million years ago. It is
named after the state of Pennsylvania where rocks of this age are widespread. Coal- forming
swamps at their fullest extent. All so-called fossil fuels (coal, oil, natural gas) are formed at
this time. First reptiles.
Permian Period 286 million – 248 million
The final period of the Paleozoic era, spanning the time between 286 and 248 million years
ago. It is named after the province of Perm, Russia, where rocks of this age were first studied.
Extensive glaciation of southern hemisphere. Appalachians are fully formed- about height of
Himalayas. Most of the shallow seas drain from North America. Reptiles diversify. First
coniferous trees; begin to out-compete earlier forests. Many modern insects appear. First
Archosaurs (“ruling reptiles”). Finback reptiles (Dimetridon) are major carnivores. Mass
extinction near end of Permian when 80%+ of all life goes extinct. Last trilobites extinct by 248
million years BP. AKA: Age of Reptiles
Mesozoic Era 248 million – 65 million
The word Mesozoic is from Greek meaning "middle life." An era of geologic time between the
Paleozoic and the Cenozoic, spanning the time between 248 and 65 million years ago.
Sometimes called “Age of Reptiles” but “Age of Dinosaur” is more appropriate.
Triassic Period 248 million – 213 million
The earliest period of the Mesozoic era, spanning the time between 248 and 213 million years
ago. The name Triassic refers to the threefold division of rocks of this age in Germany.
Volcanism in eastern US. Overall climate cooler. Many areas are arid (dry) to semi-arid.
Pangaea (Supercontinent) is fully formed. Continents are mountainous. Appalachians broken
into basins due to uplift. Fossil record shows fewer species (decreased diversity) but
populations of each are great. Ammonites, clams, snails in oceans.
Dinosaurs are a specific subgroup of the archosaurs, a group that also includes crocodiles,
pterosaurs, and birds. Although pterosaurs are close relations, they are not true dinosaurs.
Even more distantly related to dinosaurs are the marine reptiles, which include the
plesiosaurs and ichthyosaurs. First dinosaurs and the first primitive mammals in fossil record
at same time.
The Late Triassic (Carnian) deposits of the Ischigualasto Formation contain some of the oldest
known dinosaur remains. Of those sites containing the earliest dinosaurs, Ischigualasto ranks
second in fame, after the Chinle Formation of North America, but ranks first in the quality,
number, and importance of its dinosaur finds. It is also the only place in the world where
nearly all of the Triassic is represented in an undisturbed sequence of rock deposits, and both
the overlying and underlying formations have also yielded important fossils of early
dinosaurs as well as of early synapsids and freshwater fish.
Only about 6% of all tetrapods found there are dinosaurs. Rhyncosaurs and cynodonts are far
more common, and in fact the rhyncosaur Scaphonix accounts for half of all tetrapod fossils.
This suggests that dinosaurs were not an immediate success when they first appeared,
especially considering that Ischigualasto is relatively rich in dinosaur remains for such an
early date. Despite the rarity of these early dinosaur fossils, their importance for
understanding early dinosaur evolution is tremendous. Fossils from this site include both
early ornithischians, such as Pisanosaurus, and putative early saurischians, the two major
lineages of dinosaurs. These fossils therefore establish not only that dinosaurs existed by this
time, but that they had begun to diversify.
The carnivorous archosaur Herrerasaurus is the most numerous of these dinosaur fossils,
though there is some controversy over its true nature. While it has many of the features found
in dinosaurs, it lacks certain features of the hip and leg bones, and so may be a close dinosaur
relative, and not a true dinosaur at all. Some paleontologists point to the hipbone
arrangement, arguing that this demonstrates it is an early theropod, but this hip structure is
believed to have been present in dinosaur ancestors as well. A similar dinosaur from the
Chinle Formation of North America, Chindesaurus, shows that these early dinosaurs existed
over a large area.
Another controversial early dinosaur was found in Ischigualasto in the early 1990s. Eoraptor
lunensis, the "dawn raptor", is a smaller carnivore than Herrerosaurus, and also bears a
frustrating mix of primitive and specialized characters. Though not known from as many
specimens, nearly complete remains have been found. The small size of the fossil, and its
proportionately large eye-sockets have led some paleontologists to suggest it was actually a
much larger dinosaur, and that the fossils discovered so far are from juveniles.
Jurassic Period 213 million – 145 million
The middle period of the Mesozoic era, spanning the time between 213 and 145 million years
ago. It is named after the Jura Mountains between France and Switzerland, where rocks of
this age were first studied. North America and Africa separate. Ocean basins open.
Appalachians eroding. Pacific and North American plates collide with subduction occurring
on the western coast. Orogeny from Alaska to Mexico. Climate warmer than today.
Today, the name "Jurassic" conjures up images of the phenomenally successful book and
movie, "Jurassic Park". It is quite true that the dinosaurs dominated the land fauna -- although
many of the dinosaurs featured in "Jurassic Park", such as Triceratops and Tyrannosaurus rex,
did not appear until after the Jurassic was over. The largest dinosaurs of the time -- in fact, the
largest land animals of all time -- were the gigantic sauropods, such as the famous Diplodocus,
Brachiosaurus and Apatosaurus. Other herbivorous dinosaurs of the Jurassic included the
plated stegosaurs. Predatory dinosaurs of the Jurassic included fearsome carnosaurs such as
Allosaurus, small, fast coelurosaurs, and ceratosaurs such as Dilophosaurus. The Jurassic also
saw the origination of the first birds, including the well-known Archaeopteryx, probably from
coelurosaurian ancestors.
But there was more to life than dinosaurs! In the seas, the fishlike ichthyosaurs were at their
height, sharing the oceans with the plesiosaurs, with giant marine crocodiles, and with
modern-looking sharks and rays. Also prominent in the seas were cephalopods -- relatives of
the squids, nautilus, and octopi of today. Jurassic cephalopods included the ammonites, with
their coiled external shells and the belemnites, close relatives of modern squid but with
heavy, calcified, bullet-shaped, partially internal shells. Among the plankton in the oceans,
the dinoflagellates became numerous and diverse, as did the coccolithophorids (microscopic
single-celled algae with an outer covering of calcareous plates).
Land plants abounded in the Jurassic, but floras were different from what we see today.
Although Jurassic dinosaurs are sometimes drawn with palm trees, there were no palms, or
any other flowering plants, at least as we know them today, in the Jurassic. Instead, ferns,
ginkgoes, bennettitaleans or "cycadeoids", and true cycads flourished in the Jurassic. Conifers
were also present, including close relatives of living redwoods, cypresses, pines, and yews.
Creeping about in this foliage, no bigger than rats, were a number of early mammals.
Cretaceous Period 145 million – 65 million
The final period of the Mesozoic era, spanning the time between 145 and 65 million years ago.
The name is derived from the Latin word for chalk ("creta") and was first applied to extensive
deposits of this age that form white cliffs along the English Channel between Great Britain
and France. Lands are low and extensive. Rocky Mountains form near end of period. Africa
and South America Separate.
No great extinction or burst of diversity separated the Cretaceous from the Jurassic Period
that had preceded it. In some ways, things went on as they had. Dinosaurs both great and
small moved through forests of ferns, cycads, and conifers. Ammonites, belemnites, other
molluscs, and fish were hunted by great "marine reptiles," and pterosaurs and birds flapped
and soared in the air above. Yet the Cretaceous saw the first appearance of many lifeforms
that would go on to play key roles in the coming Cenozoic world. Marsupials, insectivores
abundant and first true flowering plants appear.
Perhaps the most important of these events, at least for terrestrial life, was the first
appearance of the flowering plants, also called the angiosperms or Anthophyta. First
appearing in the Lower Cretaceous around 125 million years ago, the flowering plants first
radiated in the middle Cretaceous, about 100 million years ago. By the close of the
Cretaceous, a number of forms had appeared that any modern botanist would recognize.
At about the same time, many modern groups of insects were beginning to diversify, and we
find the oldest known ants and butterflies. Aphids, grasshoppers, and gall wasps appear in
the Cretaceous, as well as termites in the later part of this period. Another important insect to
appear was the eusocial bee, which was integral to the ecology and evolution of flowering
plants.
The Cretaceous also saw the first radiation of the diatoms in the oceans (freshwater diatoms
did not appear until the Miocene).
The Cretaceous-Tertiary Extinction (Often referred to as the K-T boundary)
The most famous of all mass extinctions marks the end of the Cretaceous Period, 65 million
years ago. As everyone knows, this was the great extinction in which the dinosaurs died out.
(Except for the birds, of course.) The other lineages of "marine reptiles", such as the
ichthyosaurs, plesiosaurs, and mosasaurs, also were extinct by the end of the Cretaceous, as
did the flying pterosaurs -- although some, like the ichthyosaurs, were probably extinct a little
before the end of the Cretaceous. Many species of foraminiferans went extinct at the end of
the Cretaceous, as did the ammonites. But many groups of organisms, such as flowering
plants, gastropods and pelecypods (snails and clams), amphibians, lizards and snakes,
crocodilians, and mammals "sailed through" the Cretaceous-Tertiary boundary, with few or
no apparent extinctions at all. Dinosaurs extinct by end of Cretaceous.
Cenozoic Era 65 million - present
Its name is from Greek and means "new life” or “recent life”. An era of geologic time from the
beginning of the Tertiary period (65 million years ago) to the present.
Tertiary Period 65 million – 1.8 million
Name for the major portion of the Cenozoic era, the most recent of the geologic eras from
around 65 – 1.8 million years ago. The name Tertiary was first used about the middle of the
18th century to describe a layer of unconsolidated sediments geologically younger than other
deposits then known as Primary and Secondary.
Around 1830 a fourth division, the Quaternary, was added. Although these divisions of the
earth's crust seemed adequate for the region to which the designations were originally
applied (parts of the Alps and plains of Italy), when the same system was later extended to
other parts of Europe and to America it proved to be inapplicable. It was realized that one
scheme of classification could not be applied universally: The names Primary and Secondary
were generally abandoned; Tertiary and Quaternary were, and still are, used, but other
geologic literature substitutes other names, including the Palaeogene and Neogene. The main
divisions of the Tertiary are the Paleocene, Eocene, Oligocene, Miocene, and Pliocene epochs.
Sometimes the Paleocene is included in the Eocene. At the beginning of the Tertiary, the
outlines of the North American continent were very similar to those of today; by the close of
the period, Europe also had emerged substantially in its present form. Marine submergences
in Europe were moderately extensive, but in North America they never went beyond the
Atlantic, Gulf, and Pacific coasts and the lower Mississippi valley. These inundations took
place chiefly in the Eocene, Oligocene, and Miocene epochs, the continents being generally
emergent in the Pliocene epoch. The Tertiary formations of either unconsolidated sediments
or quite soft rocks are widespread. In the Tertiary, Gondwanaland finally split completely
apart, and India collided with the Eurasian plate (see plate tectonics). The previously existing
mountain ranges of North America were again elevated, the Alps, Pyrenees, Carpathians, and
other ranges were formed in Europe, and in Asia the Himalayas arose. Widespread volcanic
activity was prevalent.
At the beginning of the period the mammals replaced reptiles as the dominant animals.
Striking developments in mammalian life marked each epoch. Modern types of birds,
reptiles, amphibians, fishes, and invertebrates either were already numerous at the beginning
of the period or appeared early in its history. Some examples are marsupials, insectivores,
bears, hyenas, dogs, cats, seals, walruses, whales, dolphins, early mastodons, hoofed
mammals, horses, rhinoceroses, hippopotamuses, oreodonts, rodents, rabbits, monkeys,
lemurs, apes, and humans (Australopithecus).
Paleocene Epoch 65 million – 55.5 million
It is named after the Greek words "palaois" (old) and "ceno" (new). Earliest epoch of the
Tertiary period, spanning the time between 65 and 55.5 million years ago. Climate is mild to
cool. Wide, shallow continental seas mostly gone. In Western North America, the uplift of the
Rocky Mts. that marked the end of the Mesozoic era continued throughout the Paleocene, and
the Cretaceous inland seas gradually withdrew from the Great Plains area and central and
SW California. In Montana and Wyoming the Fort Union shales and sandstones, laid down
during this epoch, are noteworthy because they overlie undeformed upper Cretaceous
sediments, thus recording the demise of the dinosaurs and the rise of mammals. During this
epoch, the opening of the Norwegian Greenland Sea eventually resulted in a much more
significant mixing of waters, creating the cold North Atlantic Deep waters. Greenland began
separating from Europe as the northern mid-Atlantic Ridge formed. Except for part of N
France, Europe was largely emergent (i.e., above water). On the other side of the world,
Antarctica and Australia had separated; India had completed its separation with Africa,
resulting in an outpouring of basalts; and India, Africa, and Australia were about to collide
with Eurasia. By the end of Paleocene time, N America's last large sea retreated to the Gulf of
Mexico.
The Paleocene mammals were mostly small herbivores and insectivores similar to their
Mesozoic ancestors. By mid-Paleocene the ungulates, or hoofed mammals of mostly five-toed
forms, became abundant. Prosimian primates (tree shrews and tarsiers) also increased in
number. Some of the fossil evidence from Paleocene sediments is difficult to explain; Alaska,
for example, clearly had broad-leafed evergreen floras that typically grow in tropical forests.
As the land has not changed significantly in latitude since the Paleocene, the evidence of
these floras is a puzzle. First known primitive primates and mammalian carnivores. Some
modern plants are present.
Eocene Epoch 55.5 million – 33.7 million
Its name is from the Greek words "eos" (dawn) and "ceno" (new). An epoch of the lower
Tertiary period, spanning the time between 55.5 and 33.7 million years ago. Climate is now
mild to tropical. Many lakes in western North America. Australia separates from Antarctica.
India collides with Asia.
The second epoch of the Tertiary period. The Eocene in North America was marked by the
submergence of the Great Valley of California and a portion of the Atlantic and Gulf coastal
plain extending from New Jersey to Texas and into the present Mississippi River valley as far
north as S Illinois. There was also extensive sediment deposition in the Rocky Mt. region.
Eocene sedimentary formations along the Atlantic-Gulf coast are chiefly sands, clays, and
marls, with some limestone and lignite; in California, Oregon, and Washington they consist of
shale and sandstone, with oil and coal. The Badlands of the West are partly cut into Eocene
rock formations, e.g., the Wasatch, Green River, Bridger, and Uinta formations, which contain
great quantities of volcanic ash and, in some districts, oil-producing shale. The Green River
formation of SW Wyoming is noted for its freshwater fossil fish. The brightly colored
Wasatch formation makes up the spectacular pillars of Bryce Canyon National Park.
Interpretation of Eocene rock strata is based on the succession of beds in Belgian, French, and
English basins, which became type areas. The Norwegian-Greenland Sea began to open
during the Eocene, and a great inundation from the Mediterranean covered most of S Europe,
N Africa, and SW Asia, depositing nummulitic limestone, which is prominent in the Alps and
Carpathians and from which the stones of the Pyramids were quarried.
Primitive horses, tiny camels, modern birds and gigantic birds present. Hardwoods and
redwoods in western US. Grasslands expand. Mammals became the dominant animals, and
the ancestors of the common animals of Europe and North America made their appearance,
possibly as immigrants from other regions. Eocene mammals included ancestral rhinoceroses,
tapirs, camels, pigs, rodents, monkeys, whales, and the ancestral horse, eohippus, as well as
animals such as the titanothere, which have since become extinct. The vegetation of the
Eocene was fairly modern; the climate was warm.
Oligocene Epoch 33.7 million – 23.8 million
It is named after the Greek words "oligos" (little, few) and "ceno" (new). An epoch of the early
Tertiary period, spanning the time between 33.7 and 23.8 million years ago. Himalayas and
Alps rise from the subduction of India and Asia. Red Sea forming due to separation of Africa
and Arabia. Rockies are volcanic. California collides with mid-Pacific Ridge.
The third epoch of the Tertiary period. More of North America was dry land during the
Oligocene than in the preceding Eocene epoch. The Gulf Coast was flooded, but the Atlantic
coast N of South Carolina became emergent; the principal formation of the Gulf district was
the Vicksburg limestone. The Pacific coast, like the more northern Atlantic coast, was largely
elevated; erosion led to the deposition of the Oligocene portion of three sediments (the Sespe
conglomerate, sandstone, and shale), which contains red beds like those of the Permian
period. The great erosion of the Rockies was responsible for the deposition of the fossil-rich
White River clays and sands over large areas of W Nebraska and NE Colorado and parts of
Wyoming and the Dakotas. Late in the Oligocene, the John Day deposits of volcanic ash,
notable for their included fossils, were formed in Oregon. In S Europe, the formations are
somewhat similar to those of the Eocene; a sandstone and shale formation, the Flysch, was
laid down in regions adjacent to mountain systems. The Alpine mountain building episode
reached peak intensity as Africa further impinged against the Eurasian plate. In the middle
Oligocene a sea extended over N Europe as far east as the Urals and was connected with the
greater Mediterranean through the present Rhine valley. There are extensive deposits of
Oligocene lignite in Germany, indicating swamp conditions either before or during the flood,
and the Alsatian potash, salt, and gypsum are Oligocene. During the Oligocene there was
considerable volcanic activity in central Europe, Scotland, Ireland, and Iceland, as well as in
the San Juan Mts. of Colorado and the Absaroka Mts. of Wyoming where remnants of this
volcanism persist in Yellowstone National Park.
The life of the Oligocene was marked in Europe and North America by the virtual
disappearance of the archaic mammals of the Paleocene. Carnivorous mammals—ancestral
canines (wolves) and Felines (cats)—made their appearance, along with beavers, mice,
rabbits, and squirrels. A more highly developed type of horse, giant hogs, and camels were
other new arrivals. The titanotheres—mammals remotely related to the horse and the
rhinoceros evolved to types of great size, then died out. The brontotherium, which appeared
in North America, was the largest mammal to ever live on that continent. Running and
aquatic rhinoceroses developed. The earliest elephant and a primitive anthropoid ape
appeared in Africa. The climate of the Oligocene was mild and temperate in North America.
Large browsing mammals. True apes appear. Origin of many modern families of flowering
plants. Early rhinoceros (baluchitherium (largest land animal that ever lived)) and elephant
(mastodon) present in fossil record.
Miocene Epoch 23.8 million – 5.3 million
It is named after the Greek words "meion" (less) and "ceno" (new). A epoch of the upper
Tertiary period, spanning the time between 23.8 and 5.3 million years ago. Climate is
moderate. Southern hemisphere experiences another round of extensive glaciation. Rockies
continue to uplift. Volcanic activity produces the Cascade Mountains. South America and
Antarctica separate. Andes Mountains forming.
The fourth epoch of the Tertiary period. North America was more extensively submerged in
the Miocene than in the preceding Oligocene epoch and underwent considerable crustal
disturbances. The Atlantic and Gulf coasts were flooded about as extensively as in the Eocene
epoch. Miocene rocks are found along the Atlantic as far north as Martha's Vineyard, but the
series, everywhere thin, is thickest and least interrupted from New Jersey to Maryland. On
the Gulf coast it extends from Florida westward to Texas. The Atlantic series is chiefly marls,
clays, and sands, with diatomaceous earth; the Florida series, chiefly limestone (Florida
having risen as an island in the late Oligocene); the Gulf series, limestone and clastic
sediments.
On the Pacific coast, the Great Valley of California was submerged at the beginning of the
Miocene. The deposition of the Vaqueros sandstone, clay, and conglomerate was followed by
the formation of the oil-rich Monterey series, partly sandstone and shale but largely
diatomaceous tufa. In mid-Miocene time there was extensive mountain building in this
region; the Cascades and Coast Ranges were elevating, although the Rocky Mts. had by then
eroded to low relief. This disturbance was accompanied by volcanic activity—the Columbia
and Snake River plateaus consist of over 200,000 sq mi (520,000 sq km) of basaltic lava flows
up to 10,000 ft (3,000 m) thick—and by the first known movement along the San Andreas
fault zone, engendered by the collision of the North American continental plate with the
Pacific Ocean plate.
Late in the Miocene a new, extensive submergence resulted in the deposition of the San Pablo
shale and sandstone. The sediments of the California Miocene came chiefly from the Sierra
Nevada and the Klamaths, which, through erosion, were peneplained by the close of the
epoch. In the western interior of North America the Columbia River basalt plateau of Idaho,
Washington, Oregon, N California, and N Nevada was formed by a great outpouring of lava,
which continued in the succeeding Pliocene epoch.
During the Miocene most of N Europe was elevated, but marine waters covered E Spain, S
France, Italy, and a depressed area extending through Hungary to a basin around Vienna. In
addition to considerable orogeny, lagoons were formed at the base of the Carpathians and
north of the Caucasus in the regions now occupied by the Romanian and Baku oil fields.
The mammalian life of the Miocene was marked by further stages in the development of the
horse, by the multiplication and final extinction of the giant hogs, and by the appearance of
the mastodons, raccoons, and weasels. Cats, camels, doglike carnivores, and rhinoceroses
were common, and species of a great ape (Dryopithecus) inhabited S Europe, Asia, and Africa.
In the Miocene a distinct cooling of the climate resulted in the reduction of forests and an
increase in grassy plains.
Whales, apes, and grazing animals widespread. Forests diminish while grasslands continue
to expand. Hyena, bear, seal present.
Pliocene Epoch 5.3 million – 1.8 million
It is named after the Greek words "pleion" (more) and "ceno" (new). Final epoch of the
Tertiary period, spanning the time between 5.3 and 1.8 million years ago. Climate cooler.
Uplift and mountain-building continue and many species of animals become extinct. North
and South America connect as Panama uplifts.
This is the fifth epoch of the Cenozoic. By the beginning of the Pliocene, the outlines of North
America were virtually the same as now. Encroachments by the sea were limited to a narrow
strip along the coasts of the Carolinas, Georgia, Florida, and the Gulf Coast states, and an
embayment, smaller than that of the preceding Miocene epoch, in California. The Pliocene
formations on the Atlantic coast are chiefly marine marls; on the Gulf they are nonmarine
sediments resulting from erosion. In California they contain much volcanic ash and some are
oil-bearing. The Pliocene formations of the western interior are small and scattered. In
western interior North America and on the west coast, volcanic activity continued into the
Pliocene from the Miocene. The close of the Pliocene was marked in North America by the
Cascadian revolution, in the course of which the Sierra Nevada was elevated and tilted to the
west. The Cascades, Rockies, Appalachians, and the Colorado plateau were uplifted, and
there was activity in the mountains of Alaska and in the Great Basin ranges of Nevada and
Utah. In Europe the Pliocene sea covered small parts of the northwest of the continent and a
large area around the present Mediterranean; a number of volcanoes were active, among
them Vesuvius and Etna. There was considerable mountain building, including the folding
and thrusting of the Alps.
The climate of the Pliocene was markedly cooler and drier than that of the Miocene and
foreshadowed the glacial climates of the Pleistocene epoch. The life of the Pliocene was
notable for its modern appearance; the Pliocene marked the climax, and perhaps the initial
decline, of the supremacy of the mammals.
Large carnivores prowl grasslands. First appearance of upright hominids (Australipithicenes)
Quaternary Period 1.8 million - present
It is named after the Latin word "quatern" (four at a time). The second period of the Cenozoic
era, spanning the time between 1.8 million years ago and the present. It contains two epochs:
the Pleistocene and the Holocene. It was named (1759) by Giovanni Arduino, an Italian
scientist who thought that the biblical great flood was responsible for its deposits. During the
early Quaternary, Europe and North America were covered by the glaciers of the Pleistocene
epoch. Retreat of the glaciers led to isostatic rebound of the crust in the Holocene. In the
Quaternary the climate and present physical features of the earth continued to develop.
Significant changes in sea level within historic times are demonstrated by the submergence of
the temple of Jupiter Serapis near Naples and by the rising of the shores of the Baltic. The life
of the Quaternary has been marked by the rise and dominance of humans.
Pleistocene Epoch 1.8 million – 8,000
It is named after the Greek words "pleistos" (most) and "ceno" (new). An epoch of the
Quaternary period, spanning the time between 1.8 million years ago and the beginning of the
Holocene at 8,000 years ago. Climate fluctuates between mild and cool. Four major glacial
advances and retreats (AKA: Ice Age). Sierra Nevada Mountains uplift.
Analyses of the magnetic polarity in deep-sea sediment cores indicated that the Pleistocene
began around 1.8 million years ago—much earlier than had previously been suspected. Since
the interglacial periods of the Pleistocene were of longer duration than the time elapsed since
the end of the Pleistocene 11,000 years ago, it is sometimes suggested that the Holocene, or
Recent, epoch, which is occurring now, may be merely another such interglacial stage and
that the glaciers may return at some future time.
Among the characteristic Pleistocene mammals of North America were at least four species of
elephants, including the mastodon and the mammoth, true horses, of the same genus as the
domestic horse though not of the same species, saber-tooth carnivores, large wolves, giant
armadillos and ground sloth, bison, camels, and wild pigs. Among the arctic mammals that
ranged far south in the glacial stages were the musk ox in North America and the woolly
mammoth in Europe. The Pleistocene saw the beginning of the trend toward the extinction of
many mammal species, which continued into historic times. The Pleistocene is noted also for
the first appearance of modern humans approximately 500,000 years ago and the migration of
humans to the American continents. Large numbers of mammal species (giant mammoth,
mastodon, saber tooth cats) begin to disappear by the end of Pleistocene.
Holocene Epoch 8,000 - present
It is named after the Greek words "holos" (entire) and "ceno" (new). An epoch of the
Quaternary period, spanning the time from the end of the Pleistocene (8,000 years ago) to the
present. Glaciers retreat; warming; another interglacial period. Deserts spread on a large scale
Recent epoch, most recent of all subdivisions of geologic time, ranging from the present back
to the time (c.11,000 – 8,000 years ago) of almost complete withdrawal of the glaciers of the
preceding Pleistocene epoch. During the Holocene epoch, the sculpturing of the earth's
surface to its present form was completed. Withdrawal of the glacial ice resulted in the
development of the present-day drainage basins of the Missouri and Ohio rivers, the
development of the Great Lakes, and a global rise in sea level of up to 100 ft (30 m) as the
glacial meltwater was returned to the seas. Warming climates resulted in the poleward
migration of plants and animals.
The most significant development during the Holocene was the rise of modern humans, who
are thought to have first appeared in the late Pleistocene. All of the races of modern humans
were fully developed, with eventual worldwide distribution. Human culture developed
during this epoch from a primitive one to the complex industrial society of today, in which
humans themselves have become a significant factor in altering the earth's surface
environment. Planetary spread of modern humans Homo sapiens (AKA: “Wise Man”).
Extinction of many of the large mammals.
Precambrian
4.5 Bil - 544 Mil
Hadean
4.5 Bil – 3.8 Bil
Archean
3.8 Bil – 2.5 Bil
Proterozoic
2.5 Bil – 544 Mil
Sturtian
800 – 650 Mil
Vendian
650 Mil – 544 Mil
Phanerozoic
544 Mil - Pres
Paleozoic 544 - 248 Mil
Cambrian
544 - 505 Mil
Ordovician
505 - 440 Mil
Silurian
440 - 417 Mil
Devonian
417 - 360 Mil
Carboniferous
360 - 286 Mil
Permian
286 - 248 Mil
Mesozoic 248 - 65 Mil
Triassic
248 - 213 Mil
Jurassic
213 - 145 Mil
Cretaceous
145 - 65 Mil
Cenozoic 65 Mil - Pres
Tertiary
65 - 1.8 Mil
Paleocene
65 – 55.5 Mil
Eocene
55.5 – 33.7 Mil
Oligocene
33.7 – 23.8 Mil
Miocene
23.8 – 5.3 Mil
Pliocene
5.3 - 1.8 Mil
Quaternary
1.8 Mil - Pres
Pleistocene
1.8 Mil - 8,000
Holocene
8,000 – Pres