1. How do we know the age of the Earth?
Two methods are used by Scientists to determine the age of earth.
relative dating of fossils and rock layers
radioactive dating of fossils and rock layers

2. Fossils and Ancient Life
All information about past life is called the fossil record.
The fossil record includes information about the
structure of organisms,
what they ate,
what ate them,
in what environment they lived,
and the order in which they lived.

3. How Fossils Form Most fossils form in sedimentary rock.
Sedimentary rock forms when exposure to the elements breaks down existing rock into small particles of sand, silt, and clay.

4. Fossil Formation Water carries small rock particles to lakes and seas.
How Fossils Form
Fossil Formation
Water carries small rock particles to lakes and seas.
The fossil record provides evidence about the history of life on Earth. Most fossils are formed in sedimentary rock.

5. Dead organisms are buried by layers of sediment, which forms new rock.
How Fossils Form
Dead organisms are buried by layers of sediment, which forms new rock.
The fossil record provides evidence about the history of life on Earth. Most fossils are formed in sedimentary rock.

6. The preserved remains may be later discovered and studied.
How Fossils Form
The preserved remains may be later discovered and studied.
The fossil record provides evidence about the history of life on Earth. Most fossil formed in sedimentary rock.

7. Interpreting Fossil Evidence
Relative Dating
In relative dating, the age of a fossil is determined by comparing its placement with that of fossils in other layers of rock.
Rock layers form in order by age— the oldest on the bottom, with more recent layers on top.

8. Interpreting Fossil Evidence
Relative Dating
In relative dating, a paleontologist estimates a fossil’s age in comparison with that of other fossils. Each of these fossils is an index fossil. It enables scientists to date the rock layer in which it is found. Scientists can also use index fossils to date rocks from different locations.
Photo credit: l. ©David Hanson/Stone; r. ©CORBIS

9. Interpreting Fossil Evidence
Index fossils are used to compare the relative ages of fossils.
An index fossil is a species that is recognizable and that existed for a short period but had a wide geographic range.

12. Interpreting Fossil Evidence
Relative dating allows scientists to estimate a fossil's age compared with that of other fossils.

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IB Assessment Statement: D.3.7 Discuss the incompleteness of the fossil record and the resulting uncertainties about human evolution
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Why is the human fossil record incomplete?
Fossils are rare, because fossilization requires certain conditions
Some body parts do not fossilize/ soft parts do not fossilize
Dead organisms are destroyed by predators, climate, water damage before they fossilize
Not all the fossils have been found
Fossils degenerate over time. Thus, the oldest fossils might be reduced to dust
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Discuss the incompleteness of the fossil record and the resulting uncertainties about human evolution (6 points)
Only part of organisms found :
Some parts of living organisms do not fossilize
Fossilization is rare and fossilization requires certain conditions;
dating only approximate;
Fossils may not be representative of the species;
Rarity of fossil formation lead to missing links in the fossil record;
Naming/ give an example of one or more hominid species found in the fossil record (accept Genus only or anglicized name, but not "Lucy");
Many aspects of human evolution (eg language) are not represented in fossil record;
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16. A sample comes from:

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IB Assessment Statements: D.3.1 Outline the method for dating rocks and fossils using radioisotopes, with reference to 14C and 40K. D.3.2 Define half-life. D.3.3 Deduce the approximate age of materials based on a simple decay curve for a radioisotope.
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18. Radioactive Dating
Radioactive dating – using the radioactive decay of isotopes to date rocks and fossils.

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Isotopes:
An isotope is a version of an element with a different number of neutrons from the usual version of the same element.
EXAMPLE: Carbon has three isotopes
Isotope
Mass Number
Protons
Electron
Neutrons
14 C
Carbon-14 14 6 8
13 C
Carbon-13 13 7
12 C
Carbon 12 12
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Radioisotopes:
Certain isotopes are unstable an in order to reach a stable state they release some of their subatomic particles.
Carbon 14 is unstable. Right now carbon 14 in your body is shooting off radioactive subatomic particles and it is becoming more stable a more stable isotope(nitrogen -14)
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22. When we die we do not take in anymore carbon atoms.
Carbon-12 is not radioactive and does not decay.
Carbon-14 decays into nitrogen-14 (Nitrogen-14 is called the daughter isotope of carbon-14) at a known rate.
Thus, by comparing the amounts of carbon-14 and carbon-12 in a fossil, researchers can determine when the organism lived.

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Determining known rates of decay of isotopes:
Unstable isotopes will decay into its more stable form at a stable rate called Half lives.
A half-life is the length of time required for half of the radioactive atoms in a sample to decay to it more stable form.
The more stable form that the radioactive atom decays into is called the daughter isotope
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25. Table 1: The below table shows radio active parent atoms and their stable daughter isotopes. It also show how long it takes for half the parent radioactive atom to decay into the daughter isotope, called the half life.
Radioactive Parent
Stable Daughter
Half life
Potassium 40
Argon 40
1.3 billion yrs
Uranium 238
Lead 206
4.47 billion years
Carbon 14
Nitrogen 14
5730 years

27. Interpreting Fossil Evidence
Radioactive dating involves measuring the amounts of radioactive isotopes in a sample to determine its actual age. Such measurements enable scientists to determine the absolute age of rocks and the fossils they contain.

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30. IBO Wants you to know the difference between Carbon-14 & Potassium-40
Geologic Time Scale
IBO Wants you to know the difference between Carbon-14 & Potassium-40

31. Carbon-14 (14C)
Carbon-14 (14C) decays to Nitrogen-14 (14N)
Scientist compare the ratio of carbon -12 to carbon-14 (14C: 12C) to determine the age of fossils.
This techniques is good for dates for fossils of the last 60,000 years

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33. Potassium-40 (40K)
Potassium-40 (40K) decays to Argon-40 (40Ar)
Scientist compare the ratio of Potassium-40 Argon-40 (40K : 40Ar) to determine the age of fossils.
This techniques is good for dates for fossils of the gives good results for the 580 million years
But it is too slow to give reliable results for the recent half million years

34. Potassium-40 (40K) decays to Argon-40 (40Ar)
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Radiocarbon dating tutorial:
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