Earth History
What is the Earth’s time scale?
• The Geological time scale is a record of
the life forms and geological events in
Earth’s history.
• Scientists developed the time scale by
fossils world wide.
• Radioactive dating (like Carbon Dating)
helped determine the absolute divisions in
the time scale.
Geological time Scale
(largest to smallest)
• Super-eon
• Eon
• Era* - 4
• Period* -11
• Epoch - Current
• Age - Current
Current
Middle
Past
Q
T
C
J
T
P
C
D
S
O
C
Question?
Tough
Contest
Judge
To
Pizza
Cook
Deliciously
So
Oscar
Could
Other Mnemonic Devices
• Chris Ordered Some Delicious Pizza That
Just Cost Twenty Quarters
• Cold Oysters Seldom Develop Many
Precious Pearls, Their Juices Congeal To
Quickly
• (Parents) Can Only Sit Down Carefully;
Perhaps Their Joints Can't Tolerate
Quickness
FOUR Eras…
• PRE-CAMBRIAN – 88% of earth’s history
• Paleozoic (ancient life)
– 544 million years ago…lasted 300 million yrs
• Mesozoic (middle life)
– 245 million years ago…lasted 180 million yrs
• Cenozoic (recent life)
– 65 million years ago…continues through present day
Pre-Cambrian
• Began with
the formation
of the Earth
4.6 billion
years ago.
• Accounts for
88% of whole
Earth History.
Paleozoic Era “Ancient Life”
• Explosion of life in the oceans began
during this era.
• Most of the continents were covered in
warm, shallow seas.
– Invertebrates were dominate
– Fish emerged which led to the arrival of
amphibians
– The early coal forming forests were also
formed during this time. Carboniferous Period
Paleozoic Era
• Divided into 6 periods:
• Cambrian period “Age of the Trilobites”
• Ordovician period First fishes evolved
and other species
become extinct
• Silurian period - Land
plants, insects and
spiders appear
• Devonian period Amphibians
• Carboniferous period
- Reptiles evolve.
Where we get most of
our coal/fossil fuel now.
• Permian period insects and reptiles
become widespread.
Trilobites
• Lived in Earth’s ancient seas
• Extinct before the dinosaurs
came into existence
• Cambrian Period is known as
the “Age of the Trilobites”
END of the Paleozoic Era
• the largest mass extinction in history wiped out
approximately 90% of all marine animal species
and 70% of land animals.
– Possible causes of this Mass Extinction Event
• Lowering of sea levels when the continents
were rejoined as Pangaea (convergent
boundary)
• Increased volcanic activity (ash and dust)
• Climate changes – cooler climate
Mesozoic Era – “Middle Life”
• At the beginning of this era the continents
were joined as Pangaea.
• Pangaea broke up around the middle of
this era.
• Reptiles became the most abundant
animals because of their ability to adapt to
the drier climate of the Mesozoic Era.
Mesozoic Era
• Dinosaurs were also very active in this era.
– First small dinosaurs appeared in the Triassic
Period.
– Larger and more abundant dinosaurs appeared in
the Jurassic Period.
• Small mammals and birds also appeared
during this era.
Mesozoic Era
• Divided into 3 periods:
• Triassic period - Turtles
and crocodiles evolve and
dinosaurs appear.
• Jurassic period - Large
dinosaurs roam the world.
First mammals and birds
appear.
• Cretaceous period Flowering plants appear,
mammals become more
common, dinosaurs
become extinct.
Mesozoic Mammals
Mesozoic Reptiles
End of the Mesozoic Era
• This era ended with a mass extinction event
about 65 million years ago.
– Many groups of animals, including the dinosaurs
disappeared suddenly at this time.
• Many scientists believe that this event was
caused by a comet or asteroid colliding with the
Earth.
Cenozoic Era – “Recent Life”
• Began about 65 million years ago and continues
today!!!!!
– Climate was warm and mild.
– Marine animals evolved.
• Mammals began to increase and evolve adaptations
that allowed them to live in many different
environments – land, air and the sea.
• This era is sometimes called the “Age of
Mammals”
Cenozoic Era
• Divided into 2 periods:
• Tertiary period - First
primates appear and
become the most
common.
• Quaternary period Humans evolve and
large mammals like
woolly mammoths
become extinct.
Today…
•
•
•
•
Today we are in the
Holocene Epoch of the
Quaternary Period of the
Cenozoic Era.
Which unit is the largest?
Which unit is the smallest?