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					The Geologic Time

  Video: Land Formation
Geologic Time Scale
 Geologic Time Scale: the record of the
 life forms and geologic events in the
 Earth’s history.
 Since the span of time is so great from
 the formation of the Earth to now,
 scientists can’t use a normal calendar
 to describe times.
Geologic Time Scale
                             Cenozoic Era 65mya
 The geologic time           Mammals
 scale is broken into        Mesozoic Era 248mya
 4 eras. These are           Reptiles
 characterized by
 the type of animal          Paleozoic Era 540mya
 that dominated that         Amphibians
 period of time.
                             Precambrian 4.6bya
Video: Geologic Time Scale
                             Single celled to none
 Extinct: When an animal or plant
 species dies out completely.
 Mass Extinction: When a large number
 of species dies out at the same time.

             Video: Extinction
Reasons for Extinctions
 Movements of continents.
 Meteorites hitting the Earth.
 Ice ages.
 Major changes in the climate.
The Four Eras
Scientists have divided the geologic
history into four eras.
 – Precambrian Time.
 – Paleozoic Era.
 – Mesozoic Era.
 – Cenozoic Era.
Precambrian Time
Precambrian Time: 540 mya to the
beginning of the Earth.
Only very prehistoric organisms lived.

        Baicalia= bacteria
The Early Earth
 Scientists hypothesize that Earth was a
 place of great chaos.
 Meteorites crashed into Earth.
 Constant violent thunder storms.
 Volcanic eruptions.
 Intense radiation from the sun.
The Early Earth

     Video: Precambrian
How Life Began
Scientists hypothesize that life
developed 3.5 billion years ago from
nonliving matter that already existed.
This matter included water, clay,
minerals in the ocean and gases in the
atmosphere. The energy present in the
early Earth caused these chemicals to
react and form DNA like material.
Early Life

Life Evolves
 For millions of years these DNA like
 molecules floated in the oceans
 reacting with each other to make more
 complex molecules.
 The reactions of these molecules may
 have led to the first cells, prokaryotic.
Prokaryotic Cells
 Prokaryotic Cells: cells without a
Early life did not need oxygen to
survive. They made their own food
from carbon dioxide through
photosynthesis and gave off oxygen as
Evolution Again?
 As the atmosphere took on more
 oxygen, it formed a shield to protect
 Earth from the sun’s rays called the
 ozone layer. This helped keep oxygen
 in the air and allowed early life to
 evolve to breathe the oxygen in the air.
 These new organisms are now called
 eukaryotes, or cells with a nucleus.
The first eukaryotes evolved over 2
billion years ago.

    Prokaryote     Eukaryote
Paleozoic Era
 Paleozoic Era: 248mya-540mya,
 means “ancient life”.
 Rocks from this era are rich in fossils
 of animals such as sponges, corals,
 snails, clams, squids, trilobites, and
 early fish and sharks.
Paleozoic Era
 The Paleozoic era begins with the
 Cambrian Explosion, in which many
 different kinds of organisms evolved.
 The Cambrian Explosion was a time of
 a great number of new species
Paleozoic Life

 Snails             Corals       Sponges

 Clams               Squids      Trilobites

          Video: Paleozoic Era
During the Paleozoic Era, plants, fungi,
and air-breathing animals colonized
dry land.
Plants provided the first land animals
with food and shelter.

Giant Ferns   Conifers   Horsetails
Fossils indicate that crawling insects
were some of the first land animals.
Near the end of the era, reptiles,
winged insects, cockroaches, and
dragonflies appeared.

 Reptiles                 Dragonflies

Permian Extinction
 The largest mass extinction known
 occurred at the end of the Paleozoic
 era, about 90% of all marine species
 died out.

  Video: Ice Age
Mesozoic Era
Mesozoic Era: 65mya-248mya, means
“middle life”, also called the age of
After the Paleozoic mass extinction
scientists think there was a burst of
evolution resulting in many new and
different species.
      Video: Mesozoic Era
Mesozoic Life

Birds               Flowers

K-T Extinction
 K-T Extinction: At the end of the Mesozoic
 era, an asteroid is believed to have hit the
 earth causing a mass extinction.
 It is believed a large asteroid hit the Earth,
 caused dust to block the sun killing all of
 the plants, the animals had nothing to eat so
 they died. Temperatures also dropped very
                                Song: Do The Dinosaur
Video: Extinction
Cenozoic Era
Cenozoic Era: 65mya-now, means
“recent life”, also called the age of
We have the most fossil information
from this era because the fossils from
this era are closest to the surface.

      Video: Cenozoic Era
    Cenozoic Life

Saber-toothed Cat                          Camels

             Mastodon and Cro-Magnon man
Cenozoic Life
 Modern humans or Homo sapiens may
 have evolved as early as 100,000 years