Transcript Geologic Time

Geologic Time
Geologic Time Scale
• Earth’s history is divided into time units
based on the life-forms that lived during
certain periods.
• When life-forms are not present then
divisions of the geologic time scale are
based on other criteria.
Major Subdivisions of Geologic
Time
• Eons-The longest subdivisions of geologic time.
Based upon the abundance of certain fossils.
• Eras- The subdivision marked by major striking,
and worldwide changes in the types of fossils
present.
• Periods-Units of geologic time characterized by
the types of life existing worldwide at the time.
• Epochs-Units of geologic time characterized by
differences in life-forms, but some of these
differences can vary from continent to continent.
Epochs
• Cenozoic epochs have special names
• Epochs of other periods usually are
referred to simply as early, middle and
late.
Organic Evolution
• Fossils show that species of organisms
have changed over time. This change is
known as organic evolution.
• Organisms that are not adapted to
changes in the environment will die out.
The organisms that have changed and
survived will cause the species to change.
Species
• A group of organisms that reproduce with other
organisms within their same group.
• Occasionally organisms of different species will
mate and reproduce, however the offspring are
usually sterile. Mules are an example of mating
between a horse and a donkey. Mules are
sterile and cannot reproduce.
• Organisms of different species sometimes look
alike but do not mate and reproduce fertile
offspring.
Natural Selection
• Charles Darwin is often referred to as the
father of natural selection.
• Natural selection is the process by which
organisms with characteristics that are
suited to a certain environment have a
better chance of surviving and reproducing
than organisms that do not have these
characteristics.
Natural Selection
• During the industrial revolution two varieties of
moth were present a light colored moth and a
dark colored moth. Because of the coal burned
in factories there was a dark coating over the
exterior of buildings, trees etc. The light colored
moths were eaten more than the dark because
they were easier for birds to see. Therefore
more of the dark moths lived and reproduced
changing the color of the species.
Artificial Selection
• Humans crossing animals and plants in
order to produce offspring with the most
desired characteristics.
Trilobite
• An invertebrate that has an exoskeleton and a
three lobed body, also a head (cephalon), a
segmented middle section (thorax), and a tail
(pygidium).
• Different kinds of trilobites lived during different
periods of time.
• Their eyes show the result of natural selection.
Eyes located toward the front of the organism
indicates a swimmer, eyes on top of the
organism indicate a bottom dweller.
Trilobites cont.
• The bodies and tails also changed over
time to adapt to changing environments.
• Olenellus is thought to be a very primitve
trilobite because it has many body
segments.
• Organisms that could not adapt to the
changing environment became extinct.
Plate Tectonics and Earth History
• One explanation for the extinction of the
trilobite is the colliding and separating of
continents many times. In the collision of
continents mountains were formed and
seas were closed. The formation of
Pangea a giant landmass, the
supercontinent, changed the environment
in which trilobites lived. This is one theory
that explains the extinction at the end of
the Paleozoic Era.