Life Science

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Life Science

• Indicator S.HS.4.2.1
• Part A

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Life Science

• Indicator S.HS.4.2.1
• Part A

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The student understands geological time is used
to understand the Earths past.
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The Geologic Time Scale
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notice these points.

1. the timeline is approximately 4.5 billion
   years.the current accepted age of the Earth
2. there are 4 eras
3. the oldest and the longest era is the
   Precambrian.approximately 4 billion yrs
4. the last 3 eras are approximately ½ billion years
   combined, or 500 million years (much shorter)

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Did you notice the proportional size differences
of each era!
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88 of the time is Precambrian

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and these points..

1. the rocks formed during the Precambrian have very
   few fossils .. not much life existed back then
2. stromatolites and blue-green algae

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Stromatolites are mounds of prokaryotic algae and
cyanobacteria.
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Look at the next slide and notice..When (how
long ago) does abundant life begin to show up in
the rock record?
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? 600 million years ago or the beginning of the
Phanerozoic

• the Phanerozoic means visible life it is an
  eon made up of 3 eras
• paleozoic ancient life
• mesozoic middle life
• cenozoic recent life

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Key points.

• the geologic time periods are based on major
  geologic events that took place
• mass extinctions
• glaciation periods
• climate changes

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Glacial event
Extinction events
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The Earth has changed over time!

• Short term changes (occur during a humans
  lifetime)
• earthquakes change the surface of the land
• volcanic eruptions
• Long term changes (long time for them to occur)
• erosion the Grand Canyon
• mountain building the Rockies

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Earths atmosphere has changed over time!

• original atmosphere look like the gas that comes
  out of volcanoes
• water vapor
• carbon dioxide
• nitrogen
• NO OXYGEN
• oxygen begins to accumulate in the atmosphere
  about 2.5 billion years ago
• primitive organisms used photosynthesis - algae

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Radioactive Dating

• a method for age dating rocks/fossils
• radiometric dating rocks
• radiocarbon dating fossils
• parent to daughter ratio tells us how old the
  rock/fossil is
• radioactive dating allows us to assign dates to
  specific rock layers

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Kansas has sedimentary rock like limestone or
halite (rock salt)both are formed in shallow
seasKansas was under water at least 4 times in
historythe last was during the Cretaceous period
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