By Roberto Palma

1
Paleogeolosists Stratigraphy and Isotopes
(Carbon 14)

• By Roberto Palma
• October 8, 2001
• Period 4
• Biology

2
Stratigraphy

• Stratigraphy is an indirect method of determining
  the relative ages of fossils on earth
• Paleogeologists must study the strata, or layers,
  of the earth to create a rough outline of the
  earths history

3
Fossils On The Earths Stratas
4
Stratigraphy William Smith

• The relationship between layers of rock and the
  occurrence of certain fossils was noted nearly
  200 years ago by William Smith
• The English surveyor and civil engineer became
  interested in rock strata because of its
  relationship to the structural success of the
  canals he was building.
• He noticed that certain layers contained fossils,
  and that throughout England there was a match
  between the type of rock layer, its placement
  between other layers, and the fossil it contained

5
Stratigraphy Georges Cuvier and Alexander
Brongniart

• These two studied fossils in rock strata in
  France
• They compared fossils they found with modern life
  forms, and they discovered that the modern forms
  were more similar to the fossils from the higher
  rock layers than those from the lower layers
• This is because of the way fossils are formed

6
Stratigraphy How Fossils are Formed

• Sediment that settles on the top of a dead
  organism is more recent than the sediment under
  the dead organism
• We infer that any fossil that is found in a
  particular rock layer is older than the fossils
  above that layer and younger than the fossils
  below that layer

7
Stratigraphy Accurate?

• Stratigraphy helps develop estimates of the time
  period for each layer of rock, and therefore
  determine a rough idea of the age of a fossil
• Direct dating methods can determine the age of
  fossils with much greater accuracy

8
Carbon 14 How Are They Formed?
C 14 atom
Nitrogen Atom
Unstable Atom
Neutron
Proton
Nitrogen atom becomes carbon-14 atom in the
atmosphere
9
Carbon 14 How Are They Formed?
Oxygen molecule (O2)
C 14 atom
C 14 CO 2 molecule
An O2 molecule combines with a carbon-14 atom to
form carbon-14 dioxide
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Carbon 14 How Are They Formed?
Living organisms absorb C 14
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Carbon 14 How Are They Formed?
nitrogen
C 14
When an organism dies, the C 14 atoms begin to
disintegrate
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Carbon 14 Summary

• Carbon 14 becomes part of plants and animals.
  Small amounts of carbon 14 exist in the
  atmosphere as carbon dioxide, which plants
  incorporate into their tissue
• This carbon 14 enters animals when they eat
  plants
• Scientists can measure the amount of carbon 14 in
  fossils and, because they know that the half-life
  of carbon 14 is 5730 years, they can calculate
  the age of the organism

13
Isotopes

• Radioactive isotopes are elements that undergo
  decay
• Potassium is a radio active isotope which takes
  1.3 billion years for half of a sample of
  potassium-40 to convert into argon-40
• Because the rate of potassium decay is very slow,
  this method only can be used to date material
  that is more than 0.5 million years old
• If scientists know the constant rate of decay for
  an element, they can measure how much of the
  radioactive element and its decay product are
  present in a material such as rock

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The End