Ch 10 Geologic Time Sec 1

1
Ch 10 Geologic Time Sec 1

• Fossils preserved remains or traces of living
  things. Found mainly found in sedimentary rock,
  from the sediments hardening.
  
• Molds and casts are the most common fossils
• Mold hollow area in sediment in the shape of an
  organism or its parts. (ice cube tray)
  
• Cast solid copy of an organism. (ice cubes)
• Petrified minerals replace the organism to form
  a stone replica. (wood or bone)
  
• Carbon film thin coating of carbon from
  delicate parts of plants or insects.
  
• Trace Fossils evidence of the activity of an
  organism. (footprint, burrows, or scratchings)
  
• Preserved remains ice, tar, amber (pg 313)

2

• Fossils provide evidence about the history of
  life and the past environments on the Earth. They
  show that organisms and land has changed over
  time. (Antarctica used to be warmer)
• Evolution gradual change in a living thing over
  long periods of time. Millions of organisms have
  evolved. The oldest fossilized remains found on
  Earth are single celled bacteria.
• Humanlike fossils date back 5 million years.
• Extinct an organism that no longer exists.
• Paleontologists scientists who study fossils

3
Relative age of Rock Sec 10 - 2

• Relative age of rocks is a generalization or an
  estimation close to the real age.
  
• Absolute age of a rock is its real age, since it
  was formed.
  
• Law of superposition older layers of rock are
  under the younger layers. Young is on top.
  
• Scientists study extrusions and intrusions along
  with faults and gaps in geologic records, like
  unconformities, to help determine rock ages.
  
• Index fossils are useful also because they tell
  the relative ages of rock layers they are in.
  
• - Ammonites are good example along with
  trilobites.

4
Radioactive Dating Sec 10 - 3

• The oldest fossils found are in Australia, of
  reefs made from bacteria called Stromatolites.
  Their absolute age is over 3 billion years old.
  
• Radioactive decay atoms of one element break
  down to form atoms of another element.
  
• - half-life time it takes half of a
  radioactive element to decay.
  
• Dating rocks Scientists use Potassium 40
• - works well for igneous rocks, not
  sedimentary.
  
• Dating fossils Scientists use Carbon 14
• - C14 half-life is 5730 years. This makes it
  very useful for current fossils.

5
Geologic Time Scale Sec 10 - 4

• The geologic time scale is used to show Earths
  long history over the last 4.6 billion years.
  
• Divisions of Geologic Time include eras, the
  longest divisions and periods, the shorter ones
  
• The 4 Eras of Geologic Time include
• Precambrian 4600 mya to 554 mya
• Paleozoic 554 mya to 245 mya
• Mesozoic 245 mya to 66 mya
• Cenozoic 66 mya ago to present day
• mya million years ago

6
Early Earth Sec 10-5

• Earth formed about 4.6 billion years ago when the
  sun and other planets formed. The oldest rocks
  on the Earth are about 4 billion years old but
  moon rocks are 4.6 billion. We think the moon
  formed at the same time as the Earth.
• Earth started as just dust, rock, ice and gas.
  (Precambrian)
  
• During the first several hundred million years an
  atmosphere, oceans, and continents all formed.
  
• Early atmosphere was 92 CO2 with a little N2
• Todays atmosphere is 78 N2 and 21 O2
• Oceans formed after the planet cooled down.
• Continents formed less than 500 million years
  after Earth formed. They move very slowly over
  the Earths surface in a process called
  continental drift.
• The first life to show up in the fossil records
  are single-celled organisms in rock, 3.5 billion
  years ago.

7
Eras of Earths History Sec 10-6

• Paleozoic Era,
• Cambrian - Mainly invertebrate animals, in the
  oceans. Brachiopods and Trilobites
  
• Ordovician 1st vertebrates jawless Fish
• Silurian plants on land were numerous
• Devonian Age of Fish, first amphibians
• Carboniferous Mississippian, Pennsylvanian,
  coal forests, 1st reptiles and winged insects
  
• Permian weather gets hot and dry , reptiles
  begin to take over
  

8

• Mesozoic Era (Age of Reptiles)
• Triassic Period first dinosaurs, hot dry
  weather, first mammals evolve.
  
• Mammals are warm blooded vertebrates with fur and
  feed young milk.
  
• Jurassic Period Largest dinosaurs, first flying
  insects, first bird Archaeopteryx
  
• Cretaceous Period first flowering plants
  seeds in fruits, many volcanoes, first snakes,
  
• - Mass extinction at the end of this period, 65
  million years ago. Many theories possible, some
  include asteroids, climate change, and evolution.

9

• Cenozioc Era (Age of Mammals)
• Tertiary Period Earths climate was warm and
  mild. Dolphins and whales show up, grass eating
  mammals show up, and birds
  
• Quaternary Period Earths climate cooled down
  causing a series of ice ages.
  
• Ocean life Algae, coral, fish, and mammals
• Land life Flowering plants, cattle, bats, dogs,
  cats, and humans became common.
  
• Giant mammals become extinct about 10,000 years
  ago when the Ice Age ends
  
• Modern humans or Homo sapiens, showed up about
  100,000 years ago in Africa. By 15,000 years
  ago, they inhabited every continent except
  Antarctica.