Geologic Time Line
October 19, 2010
Eon
Era
Period
Epoch
Old Periods
Holocene
Quaternary
Pleistocene
Neogene
Cenozoic Era
1.8 mya to Present
Pliocene
65 mya to Present
Miocene
Oligocene
Paleogene
Eocene
Paleocene
Phanerozoic
Eon
543 mya to Present
Cretaceous
Mesozoic Era
248 mya to 65 mya
Jurassic
Triassic
144 mya to 65 mya
206 to 144 mya
248 to 206 mya
Permian
290 to 248 mya
Carboniferous
Paleozoic Era
543 to 248 mya
Devonian
Silurian
443 to 417 mya
Ordovician
Cambrian
Proterozoic Era 2,500 to 543 mya
Precambrian Time
4,500 to 543 mya
Archaean 3,800 to 2,500 mya
Hadean 4,500 to 3,800 mya
354 to 290 mya
417 to 354 mya
490 to 443 mya
543 to 490 mya
Tertiary
65 to 1.8 mya
Hadean Era
• Scientists have generally thought that
during the Hadean period the solar system
was forming out of a spinning cloud of dust
and gases called an accretion disk. At the
center of the cloud, heavier particles drew
together through gravitational force until
nuclear fusion set it ablaze in light and
heat….The birth of our sun.
Hadean continued
• Scientists also believe that the Earth and other
planets would have been molten at this stage of
development. As the Earth cooled, the heavier
molten iron sank into the core, while lighter rock
rose to the surface, cooled and became the
crust. The oldest known Earth rocks to date are
approximately 3.8 billion years old. Meteorites
and lunar rocks have been found to be
approximately 4.5 billion years old.
Archaean Era
• The Archaean period was a time of
continent-building and the first stages of
early life. In fact, 70% of our continental
land masses are formed around cores of
rock, or shields, that date from this period.
• The atmosphere was perfect for bacteria.
It was filled with ammonia, methane, and
hydrogen.
Proterozoic Era
• Plate Tectonics begins…the plates were thinner
and the magma was hotter so they moved
faster. Collisions and fractures were more
frequent.
• Early plants helped develop an oxygen-rich
atmosphere. Because of this, eukaryotic cells
developed.
• Toward the end of the Proterozoic, multi-cellular
algae and the first multi-celled animals were the
result.
Paleozoic Era
• Consists of the following periods
– Cambrian
– Ordovician
– Silurian
– Devonian
– Carboniferous
– Permian
Cambrian Period
• The climate at the beginning of this period was
cold, but over time the climate in all parts of the
Earth grew warmer. This made the seas a good
place for many species to live. The continents
were still forming. They were mostly barren
rocks. The land had no plant or animal life on it
yet.
• During the Cambrian Period there was an
explosion of life forms. Most of these were in the
water. Many animals with no backbones lived in
the shallow seas. These animals were
invertebrates.
Cambrian Period
• The Cambrian Period began with an
explosion of life forms. It ended in a mass
extinction. Advancing glaciers would have
lowered the temperature of the shallow
seas where so many species lived.
Changes in the temperature and the
amount of oxygen in the water would have
meant the end for any species that could
not adapt.
Ordovician Period
• Gondwana was a huge supercontinent during
the Ordovician Period.
• During the first parts of the Ordovician the
climate was fairly warm. The land uplifted and
the continents moved around. When Gondwana
stopped its movement over the South Pole,
glaciers formed. This caused the sea level to
drop and the climate to change. These changes
led to a mass extinction at the end of the
Ordovician Period.
Silurian Period
• The climate was much warmer during the
Silurian Period. This caused the glaciers to melt
and the seas to rise. Even though the sea level
was rising, there were places where the land
was slowly rising as well. This was due to
mountain building as the continental plates
collided. In these places the seas moved away
from the coasts or evaporated from the shallow
areas. This left salt deposits. Plants that had
lived in the coastal water had to adapt to life on
land or die.
• New Life= coral and jaw-less fish
Devonian Period
• Two continents would collide to form the
supercontinent Pangaea in the Permian Period.
• Plants cover the land
• Insects and other animals find homes on the
land
• Fish with jaws developed, so did sharks
• Devonian Period ended with another mass
extinction that hurt water species more than
those on land.
Carboniferous Period
• New plants developed in the warm, humid climate and
swampy conditions of the Carboniferous Period. Large
trees covered with bark and huge ferns grew in the
middle Carboniferous swamps. The plants gave off so
much oxygen that the air had much more oxygen in it.
This allowed plants and animals to reach sizes that are
not known in today’s atmosphere. When the huge trees
and ferns died, they fell into waters that did not have
bacteria to help them decompose. These plants formed
peat beds. Eventually, with the weight of layers and
layers, these peat beds turned to coal.
Permian Period
• For most of the Permian, life on Earth was much
like it had been in the Carboniferous.
Temperatures were cooler because the
continent of Pangaea was moving northward.
Mountains were forming as the supercontinent
Pangaea moved.
• Conditions become dry and plants adapt to it.
• The Permian Extinction was largest mass
extinction that had ever occurred. No extinction
since has killed so much of the life on the planet.
In the seas, 90 to 95 percent of the species went
extinct or were severely harmed.
Mesozoic Era
• Consist of the following periods:
– Triassic
– Jurassic
– Cretaceous
Triassic Period
• It had a special climate because of the way the
land was placed on the Earth. At the beginning
of the Triassic, the land was all together in one
supercontinent, Pangaea. It straddled the
equator, so the climate was warm.
• Pangaea started to break up.
• The most important development was
happening to the reptiles. These animals would
dominate the land, sea and air throughout the
Mesozoic Era.
Triassic continued
• The first dinosaurs were evolving. The
dinosaurs were different from the
reptiles.
1)First, they were warm-blooded. This
means the temperature of their blood was
kept constant inside their body instead of
changing with the outside temperature.
2) Their bone structure was different in the
hips, legs and hands.
Triassic continued
• Another land animal developing around the
same time as the dinosaurs were the mammals.
These mammals were very small. They weren’t
very important until millions of years later in the
Cenozoic Era.
• Tree-ferns and lycopods could not live in the dry
climate of the Triassic Period.
• Instead, the conifers and ginkgos survived the
Permian extinction and developed during the
Triassic. The evergreen plants were much more
able to cope with the dry climates.
Triassic continued
• The extinction that marked the end of the
Triassic Period seemed small compared to
the one that ended the Permian Period.
Only about 20% of life in the oceans and
on land died out completely. The species
that were affected came back with
strength and would soon dominate the
world of the Jurassic and Cretaceous
Periods.
Jurassic Period
• Pangaea continued to split apart during the
Jurassic.
• The climate was warm and stable. Many types of
animals and plants developed. The numbers of
different species increased greatly during the
Jurassic Period.
• As the land pulled apart, the seas rose. Warm
shallow seas again covered parts of Laurasia
(North America and Eurasia). With the warm
seas touching the land, the climate became
more humid and tropical. Plants grew thick and
tall.
Jurassic Park FYI
• There are many misunderstandings about
dinosaurs. Movies and TV have led us to
believe many things that aren’t really true
about how and when dinosaurs lived. For
example, the movie Jurassic Park included
Tyrannosaurus Rex and Velociraptors as
some of the “star” dinosaurs. In fact,
neither T-Rex nor Velociraptors existed
until long after the Jurassic Period was
over.
Jurassic continued
• Mammals continued through the Jurassic
Period. They remained small. Many
different species developed, but the
mammals were still not playing a large part
in the day-to-day life of the Jurassic.
• There is a minor mass extinction at the
end of the Jurassic Period.
Cretaceous Period
• The changes to the continents continued
in the Cretaceous Period. Laurasia and
Gondwana continued to move apart.
• In Gondwana, South America and Africa
broke apart.
• The most famous dinosaur of all, the
Tyrannosaurus rex, finally came along
during the Cretaceous Period. They ruled
the land at the end of the Cretaceous
Period.
Cretaceous continued
• The most important development of the
Cretaceous Period was the growth of
flowering plants. Before this, most of the
trees had been gymnosperms or plants
with cones. Now trees began to produce
flowers.
• With flowers came many insects including
butterflies, ants, termites and bees.
• Mammals continued to exist during the
Cretaceous Period, but they were not very
important. These were tiny creatures
compared with the giant dinosaurs.
KT Event
• There seems to have been a major event that
caused the mass extinction at the end of the
Cretaceous Period. It is called the KT event.
• A popular theory is that a meteor hit the earth in
the Gulf of Mexico off the Yucatan Peninsula.
This caused many geologic activities. Volcanoes
erupted. Clouds, smoke and dust covered the
skies keeping the sun’s light away from the
planet for years. This would have caused huge
changes in the climate and vegetation.
Major Extinction
• The KT event caused the extinction of
more than 70 % of the species that lived in
the oceans and 15% of the species on
land. In fact, all land animal species over
50 pounds seem to have become extinct.
Nearly all dinosaurs became extinct at this
time.
Cenozoic Era
• Cenozoic Era consists of 2 Periods, but
each is broken down into smaller epochs.
– Paleogene
– Neogene
Paleogene Period
• The beginning of the Paleogene Period
was very warm and moist compared to
today’s climate. Much of the earth was
tropical or sub-tropical. Palm trees grew as
far north as Greenland!
• By the end of the Paleogene, during the
Oligocene Epoch, the climate began to
cool.
Geographic Events in the
Paleogene
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Oligocene Epoch
Australia separates from Antarctica
India crashes into Asia creating the Himalayan Mountains
Antarctica is covered by glaciers
Sea levels are low
Eocene Epoch
North America and Europe separate
Paleocene Epoch
Europe and North America are joined together
Australia is joined with Antarctica
India is not yet connected with Asia
The Atlantic Ocean is small because South America and Africa have
just separated
Mammals appearing during
Paleogene
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Oligocene
Dogs
cats
pigs
toothed whales
Eocene
bats
elephant ancestors
whales
eohippus-the first horse
Paleocene
The condylarths-ancestors of mordern hoofed herbivores
rodents
the first primates
Neogene Period
• The Neogene Period was a time of big
changes for the earth. The climate
became cooler and drier. Grasslands
replaced forests. The animals had to adapt
to these changing conditions or face
extinction.
• Drop in sea levels opened up land bridges
between continents. This allowed animals
to migrate between continents.
Neogene continued
• South America moved to the north. By the
Pliocene Epoch it merged with North
America forming the Isthmus of Panama.
Armadillos, porcupines, ground sloths and
opossums migrated from South America to
North America. Dogs, cats, bears, and
horses from North America crossed into
South America.
Neogene continued
• Many of the areas that had been covered
by forests were changing to grasslands.
Grasses were better suited to the cool dry
weather.
• Changes in the plants meant that the
animals had to adapt or die.
• New predators evolved for the grassland
environments of the Neogene Period. The
grazing animals could run fast. Predators
had to adapt or go hungry.
Neogene continued
• Sharks developed new species. One of
these new sharks was Megalodon. It
appeared first in the Miocene Epoch about
16 million years ago. Megalodon was the
largest of all the sharks.
Neogene continued
• By the end of the Pliocene Epoch the
earth was locked in an Ice Age. There
were many reasons that this happened.
The lower sea levels, new mountains and
shifting ocean currents all contributed. Ice
caps grew over the polar regions. They
stretched far beyond their present
locations. Glaciers, growing from the ice
caps, reached down as far as Ohio in the
United States.
Quaternary Period
• The Quaternary Period began with an ice
age about 1.8 million years ago. It is often
called the Age of Humans.
• It continues up to the present time and is
the period that we live in.
• During the quaternary period the positions
of the continents were much the same as
they are today. What has changed during
this time is the climate.
Quaternary continued
• There is a reason the polar ice advances
and retreats. It isn’t random. The
variations are because of changes in the
Earth's orbit. These are called
Milankovitch cycles. The last major glacial
advance was about 18,000 years ago.
Some scientists say that we are still in an
ice age and the current warming trend is
just an interglacial period or temporary
retreat of the polar ice.
Quaternary continued
• For us, the most important development of
the Quaternary Period is the development
of the hominids: Humans. From the first
primates in the Tertiary Period to modern
man, the hominid species has evolved
amazing abilities.
• Their larger brains allowed a level of
thought and feeling that was, and is,
unique among the animals