Geologic%20Time%20Scale

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Geologic Time Scale
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Imagine putting everything that has happened on
Earth into a one hour time frame!
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• Geologic Time in 24 Hours
• 1200am Earth forms
• 700am - Earliest one-celled organisms appear.
• 700am-900 pm- Simple, soft-bodied organisms
  like worms
• Little past 900pm - Complex organisms evolve in
  oceans
• Little past 1000pm - Reptiles and insects first
  appear
• Just before 1100pm - Dinosaurs arrive
• 1130pm - Dinosaurs go extinct
• 115959 - Humans appear one second before
  midnight

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Geologic Time Scale

• A record of the life forms and geologic events in
• Earths history.
• Scientists placed Earths rocks in order by
  relative age
• to create the geologic column.
• We developed the scale by studying these rock
  layers
• and index fossils.
• Radioactive dating helped us determine the
  absolute
• date of the divisions in the scale.

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Geologic Time Scale
NEW
OLD
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Divisions of Geologic Time

• As they studied the fossil record, they found
  major changes in life forms at certain times.
• They used these changes to mark where one unit of
  geologic time ends and the next begins.
• Divisions of the geologic time scale depend on
  events in the history of life on Earth.

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Divisions of Time

• EON largest division of geologic time
• ERA 2nd largest, includes two or more periods
• PERIOD 3rd largest, unit into which eras are
  divided
• EPOCH 4th largest, the subdivision of a period
• EON gt ERA gt PERIOD gt EPOCH

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• Why is a time scale used to represent Earths
• history instead of a calendar?
• Earths history is so long
• When did Geologic time begin?
• 4.6 billion years ago
• When does Geologic time end?
• It doesnt. We are now in the Quaternary Period
  of
• the Cenozoic Era.
• How long is a geologic period?
• A period doesnt have an exact length.

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EONS

• Hadean rocks from meteorites and moon
• Archean earliest rocks on earth form
• Proterozoic organisms with well developed cells
• Phanerozoic means visible life
• well represented in the fossil record

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ERAS

• Paleozoic early life 544 ? 244 mya
• Mesozoic middle life 245 ? 66 mya
• Cenozoic recent life 66mya ? present
• Which one do you live in today?

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PERIODS
PAST PRESENT

• Cambrian Explosion of life
• Ordovician 1st Vertebrates
• Silurian 1st Land Plants
• Devonian Age of Fish
• Mississippian Winged insects
• Pennsylvanian First reptiles
• Permian Age of Amphibians
• Triassic First Dinosaurs/Small mammals
• Jurassic First Birds/Flowering Plants
• Cretaceous Heyday of Dinosaurs
• Tertiary Mammals Thrive
• Quaternary Age of Man/Technology

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RememberEarly Earth

• Earth formed 4.6 billion years ago.
• Scientists think that Earth began as a ball of
  dust, rock and ice.
• Gravity pulled this mass together.
• As Earth grew larger, gravity increased. Pulled
  in nearby dust, ice and rock.
• As objects hit Earth at high speeds, their energy
  changed into thermal energy.
• Energy from collisions caused Earths temp to
  rise until planet was very hot.
• Scientist believe Earth may have become so hot it
  melted.
• Denser materials sank toward the centerformed
  Earths dense iron core.
• At same time, Earth continuously lost heat to
  cold of space.
• Less dense molten material hardened to form
  Earths outer layers. Oceans form.

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Life Develops

• We have fossils of single-celled organisms in
  rocks that formed 3.5 billion years ago...
  probably in early ocean
• Primordial Ooze water contained
• the building blocks of life
• Similar to present day bacteria.
• About 2.5 billion years ago, simple organisms
  began using energy from sun to make their own
  food.
• Photosynthesis slowly released oxygen into air.

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Cyanobacteria are some of the oldest organisms on
Earth, at least 3.5 billion years old
Filamentous  procaryotic microfossils from 3.5
Billion year old black cherts of the Archean
Warrawoona Group
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Mass Extinction

• Occurs when many living things go extinct at the
  same time (Impacts plants and animals on land and
  in sea)
• Only happened twice in Earths history.
• 1st Between Paleozoic and Mesozoic Eras
• Trilobites suddenly went extinct. Think climate
  change from continental drift may have caused
  extinction. Formation of Pangaea caused deserts
  to expand in tropics. Sheets of ice covered land
  closer to South Pole. Organisms could not
  survive.
• 2nd Between Mesozoic and Cenozoic Eras
• Wiped out over half of all plant and animal
  groups on Earth. No dinosaurs survived
• Two Theories
• Asteroid hit earth. Impact threw huge amounts
  of dust and water into atmosphere blocking
  sunlight. No sun plants died and plant eating
  animals starved. Clouds also caused temperatures
  to drop.
• Climate changes were caused by increased
  volcanic activity. Volcanic output would
• block sun as well and same process would
  follow.

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Most Accepted Theory
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Cambrian Period

• Cambrian Explosion-so many new life forms
  appeared within a short time.
• 1st time organisms had hard parts-shells and
  outer skeletons.
• All animals lived in the sea.
• Many were invertebrates-jellyfish, sponges, worms
  drifted through the water.
• Brachipods (clams) and trilobites were common in
  the Cambrian seas.

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Ordovician Period

• Seas still cover the earth
• Ice cap covers what is now North Africa.
• Ancestors of squid and octopus appear.
• Jawless fish evolvefirst vertebrates.

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Silurian Period

• Coral reefs develop.
• Prior to this period, only one-celled organisms
  lived on land. Land plants appear.
• Fish with jaws appear.
• Insects and spiders appear.

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Devonian Period

• Often called Age of Fishes.
• Every main group of fishes were present in the
  ocean.
• Most fish had jaws, skeletons and scales on their
  bodies.
• Sharks appeared late in the period.
• Animals begin to invade land.
• 1st vertebrates on land were lungfish. 1st
  amphibians evolved from the lungfish.

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Carboniferous Period

• Broken into Mississippian and Pennsylvanian.
• Life expanded over continents. Appalachian
  Mountains began to form.
• Small reptiles developed
• Winged insects evolved-huge dragonflies and
  cockroaches.
• Giant ferns cone bearing plants and trees
  formed. Coal forest

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Triassic Period

• Fish, insects, reptiles and cone bearing trees
  survived Permian extinction.
• 1st dinosaurs appear.
• 1st mammals appear-size of mouse.
• 1st turtles and crocs appear.
• Conifers, palm-like trees (cycads), ginko trees
  dominate forest.
• Pangaea holds together. Hot, dry conditions
  dominate center of Pangaea.

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Jurassic Period

• Dinosaurs become dominant land animal.
• Some were plant eaters, some were meat eaters.
• Different types lived at different times.
• 1st birds appear. Archaeopteryx means ancient
  wing thing.
• 1st flying reptiles-pterosaurs appear.
• Pangaea breaks apart-N. America and S. America
  separate.

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Cretaceous Period

• Continents moved toward present location.
• Widespread volcanic activity.
• Flying reptiles and birds competed.
• Birds hollow bones and feathers made them better
  adapted.
• 1st flowering plants. Flowering plants produce
  seeds that are inside fruit. Fruit helps seed
  survive.
• Dinosaurs dominate-T-rex.
• 1st snakes appear.

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Tertiary Period

• Climate was warm and mild.
• Rockies and Himalayas form.
• Continental glacier covers Antarctica.
• 1st grasses appear-provide food source for
  grazing animals. (ancestors of cattle, deer,
  sheep.)
• Flowering plants thrive.
• Ancestors of humans evolve.

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Quarternary Period

• Climate cooled-causing a series of ice ages.
• 20,000 years ago climate began to warm.
• Modern humans-Homo sapiens evolved as early as
  100,000 years ago. 12,000-15,000 humans had
  migrated around the world.
• Mammals, flowering plants and insects dominate
  land.

• Giant mammals of N. America and Eurasia
  become extinct.