How can rocks be correlated?

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Interpreting Earths History

• How can rocks be correlated?
• And
• Geologic Time Scale

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Index Fossils

• Index fossils are
• commonly found
• widely distributed
• limited in time span.
• They help in dating other fossils found in the
  same sedimentary layer.
• Humans will one day make excellent index fossils

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Correlation- DO NOT WRITE

• Correlation- or CO-RELATION (two or more things
  related) is a critical tool in the reconstruction
  of Earths history.
• Geologists try to match similar rock strata in
  different locations to see if they formed at the
  same time or under similar conditions

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Whos got the TIME?- DO NOT WRITE! In notes from
yesterday

• RELATIVE order/sequence known, but not the
  actual date of occurrence.
• ABSOLUTE actual date known. If 2 dates are
  known, then the RATE OF CHANGE can be known- such
  as Mountain Building.

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First Things FirstorHowd that get there? (DO
NOT WRITE)

• In the 17th C., Nicolas Steno made an important
  observation
• "Sediments are usually deposited in horizontal
  layers." This was called ORIGINAL
  HORIZONTALITY

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REVIEW DO NOT WRITE

• SUPERPOSITION sedimentary sequence will be
  OLDEST on BOTTOM (if undisturbed).
• CROSS-CUTTING igneous rock is younger than rocks
  it has intruded (cut across).
• INCLUDED FRAGMENTS pieces of rock found IN
  another rock must be OLDER (formed first).

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Geologic Time(WRITE THIS)

• Using our best data, the Earth is about 4.6
  billion years old
• Thats 4,600,000,000 years!

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How do we know the Earths age, and which rocks
are older?

• No one was around to tell us the age.
• Many experiments using radiation found in rocks
  tell us.
• The Law of Superposition can also help tell
  which rocks are older than other rocks.

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DIVIDING UP THE EARTHS AGE

• ESRT page 8 (ESRT is behind page 264 in RRB)
• Just as we have hours and minutes, the Earths
  time has also been broken up into units called
  ERAS.
• The ERAS do not have a set amount of time like
  the hour. Some ERAS, then, are longer than
  others.
• ERAS are broken down farther into PERIODS.

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THE CENOZOIC ERA

• We are currently living in the Cenozoic Era.
• The Cenozoic Era has lasted for about 63 million
  years.
• There are only two periods in the Cenozoic Era
• The Tertiary Period
• The Quaternary Period - the current period

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THE MESOZOIC ERA

• Known as the Age of the
• Dinosaur
• Started about 265 million years ago.
• Contained three periods
• The Triassic
• The Jurassic
• The Cretaceous

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THE PALEOZOIC ERA

• Known as the Age of Fish
• Started about 570 million years ago.
• Lasted about 340 million years
• Toward the end of this era coal began to form.

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The PRECAMBRIAN

• Known as Age of Bacteria
• During much of this time there was no life on
  earth.
• The earth was still hot
• The atmosphere was not like it is now.
• The Precambrian Era lasted for the first 4
  billion years of Earths history.

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EARTHS GEOLOGIC ERAS- DO NOT WRITE

• PRECAMBRIAN -rocks form, atmosphere
• PALEOZOIC -fish, amphibian,coal forms,
  Appalachian Mt. peak
• MESOZOIC -dinosaur, birds, flowers
• CENOZOIC -horses, humans, last ice age