DO NOW

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DO NOW

• What is stratigraphy? Write a statement about the
  age of the various layers (and fossils that may
  be found in those layers) you observe in the
  strata model below.

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Paleontology
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What similarities are exhibited by these horses?
What differences?
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Fossils, defined

• The remains or impression of a prehistoric
  organism preserved in petrified form or as a mold
  or cast in rock.

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Paleontology Essays Debrief

• Fossils can be formed in many ways
• Mineral replacement
• Cooled ash/lava encasing an organism
• Arctic Ice (mammoth)
• Tree Sap (insects)
• Footprints (trace fossils)
• Bones are a typically fossilized tissue.

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• The theory of Pangea/plate tectonics suggests
  that changes in land connections allowed some
  living organisms to move to new areas.
• This changed the environment in which certain
  things lived.

How do you think the movement of plates affected
GROUPS of organisms living in Earths past?
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Dating Fossils

• There are a few ways to determine age of fossils
• Indirectly, based on where it was found
  (relative dating) younger vs. older
• Directly, based on the fossil itself (absolute
  dating) using elements that make up the fossil
• Go chemistry!
• Radiometric Dating types
• Radiocarbon Dating (fairly young organic
  material uses Carbon-14)
• Potassium-Argon Dating (rocks)
• Uranium-Lead Dating (realllly old rocks)

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• Radioactive Isotope Elements that undergo steady
  decay and can be useful for determining the age
  of objects.
• Examples C-14
• Half-Life is a measurement of time involving
  radioactive isotope decay
• One half-life is the amount of time it takes for
  half of the atoms in an object to change into
  something else (which varies for each
  element/substance). This change is considered to
  be the decay.
• Scientists can apply the concept of half life and
  calculate approximate age by looking at how much
  stuff is left in the object (usually a fossil,
  rock, or something they are interested in dating
  haha. Get it?).

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Lets model decay!

• Fossil a rock of MMs

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What do you understand from this diagram? How
does half life apply?
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So, if you have a fossil (or rock surrounding
it), how can you know how old it is?

• Title a new page Carbon 14 Dating

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No problemo!

• The half life of iron-59 is 45.1 days. If you
  start with a 36g sample, how long will it take
  until you only have 1.13g left? How many
  half-lives did that process take?

No. of Half Lives Time Amount of Sample Left

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Try this

• The half life of Iodine-131 is 8.1 days. How much
  of a 20g sample will be left after 32.4 days?
  What does 131 refer to?

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Isotopes Commonly Usedfor Radiometric Dating
Isotopes Isotopes Half-life(years) Effective Dating Range(years)
Dating Sample Key Fission Product Half-life(years) Effective Dating Range(years)
Lutetium-176 Hafnium-176 37.8 billion early Earth
Uranium-238 Lead-206 4.468 billion 10 million to origin of Earth
Uranium-235 Lead-207 704 million 10 million to origin of Earth
Rubidium-87 Strontium-87 48.8 billion 10 million to origin of Earth
Potassium-40 Argon-40 1.277 billion 100,000 to origin of Earth
Carbon-14 Nitrogen-14 5730 40 0-100,000

Note the half-life durations listed in the text sections of this tutorial are rounded off foruranium-238 and potassium-40.
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Your Tasks

• Continue The Half Life of MMs Lab
• Begin practice set Radioactive Isotopes, Atoms,
  Radioactive Dating and Half Life
• Complete at least 5 of the practice problems
• Due Monday (yes, both!)