Age of meteorites and the earth – Claire Patterson (1956)

Radiometric dating was started in 1905 and was invented as a method of determining the age of the earth by Ernest Rutherford. In the time since then there has been much interest in definitive dating of the earth using uranium-lead ratio dating, lead-lead ratio dating, potassium-strontium dating, etc. along with a defendable computation. While our discussion will conclude with focus specifically on the 1956 Patterson paper, the radiometric methods used and the error associated with each method, more background discussion on the formation of the solar system, how radiometric dating works, and the characters involved in Patterson’s work will be explored. While reading the paper think about the association between these meteors and the earth, the reasons for using the isotopes used for radiometric dating, and a review of isochrons would be helpful.

http://www.mantleplumes.org/WebDocuments/Patterson1956.pdf

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11 Responses to “Age of meteorites and the earth – Claire Patterson (1956)”

  1. Porter Marsh Says:

    Ok after reading the paper I have a few questions:
    First, why is Argon abbreviated as A instead of Ar? Table 2 looks at the A40/K40 ratios. Don’t they mean Ar instead of A? or is there a difference between A and Ar that I’m not aware of?
    Second, if Thomson and Mayne didn’t use a standard to compare the emission of their sample against, how accurate can their A40/K40 be? The results were included so I’m inclined to think the results as still reliable without a standard.

    • Adam Settimo Says:

      The A is just a different notation. The paper is discussing potassium/argon decay. As for your second question, the data from these other papers is not being used to make conclusions about his own work. Patterson is using his work to evaluate the ages proposed by the other people and trying to show how errors can account for discrepancy.

  2. Hunter Burgin Says:

    My question deals with figure two from the 1956 Patterson paper. I understand that the graph shows the relationship between common earth leads and the meteoritic lead isochron. In the paragraph preceding graph two Patterson mentions that the circle along the meteoric lead isochron represents the oceanic sediment concentration for lead. What is the significance of oceanic lead sediment and how does it play into dating the earth’s age in regards to figure two specifically?

    • Adam Settimo Says:

      The problem with finding a lead sample on earth for Patterson, that represents the age of the earth, offered some problems. Because people had been contaminating the earth with lead through their gasoline and other industrial products he could just walk outside to take a core sample without getting inconsistent data. Going to the deep ocean sediment not only took care of this, but also gave him a sample that was representative of when the earth cooled and trapped isotope. By using this he could show that the lead isotope composition on earth fell on the line of the isochron, indicating that the earth is the same age as the meteorites.

  3. Antony Says:

    Does the fact that meteorites are estimated from the paper to be about 4.5E9 year old and that this number matches up with the age of the earth give some credit to the math in itself? There are multiple factors about meteorites that could and obviously do skew the math. The meteorite is assumed to be the same mass all this time even though it could have fissured, evaporated, or collided with outside matter/energy. Can’t solar flares or wild gamma rays change the decay of isotopes? Are the odds and influence of outside factors so dismal they can be discredited as lying within the margin of error or irrelevant?

    • Daniel Begay Says:

      When is comes to your question about a change in the mass of the meteorite, It seems to be discussed on the third page. That one of the common criticisms about this method is whether or not they take into account “the process of division or agglomeration of the meteoritic material”. They discuss (toward the end of the paper) the relationship of the Earth lead and the meteorite lead, and postulate that if they U/Pb ratio in the sample satisfies the expression for premordial lead and the age of the meteorite, it can be used to find the age of the earth.

  4. Kevin Greenwood Says:

    It is unclear how many oceanic sediment samples were used in this research, but it seems like he is using only one. Is this right? It is likely the sediment sample was taken near Pasadena, but because it is not specified, could it have come from anywhere? It seems like this would make a difference. If the sample were to come from somewhere near the coast of Gabon (where the world’s only natural self-sustaining fission reactor was located ~150 miles from the ocean), Patterson would have had different data. Although I can see how ocean sediment gives a better average representation of lead isotope ratios than say a single galena sample, shouldn’t samples from a number of locations be run?

    • Adam Settimo Says:

      I’m not sure where this specific sample was taken, but he did take several samples throughout his career in the Pacific, Atlantic, and in the Mediterranean. If the sample was not representative then it wouldn’t have fallen on the isochron line.

  5. Josh Ellsworth Says:

    It seems that Patterson’s paper hinges on the assumption that earth is a closed system, which makes sense to the degree that one would be concerned with. Does the fact that the lead ratios for meteorites and terrestrial samples both fit the predicted line imply that there is a uniform age of accretion for iron and silicate bodies within the solar system?
    Couldn’t Patterson could be even bolder in the paper and assert the age of the solar system proper, since after the initial agglomeration of material one can’t tell the difference in terms of isotopic distribution, and similar species would form at the same time.
    Are there other isotopic ratios used for determination of age of materials, or are the methods described in this paper still the main ones used today?

    • Adam Settimo Says:

      Patterson is operating under the assumption that all of the solar system is the same age and that the meteorites were formed at the same time as earth. Since they were smaller objects that cooled very soon after formation the isotopes within them were trapped by the mineral crystals within them. In this case zircon. because the earth took a little longer to cool the isotopes of interest were not trapped until a little later, making their age just a little shorter by this measurement method. This is why the meteor age is of more interest.

      And as far as I could see these are still the same methods used today. The type and expected age of the sample is what decides what isotopic materials are used as each has different age ranges of effectiveness.

  6. Daniel Begay Says:

    As I commented earlier in response to Tony’s questions, I have a couple more questions dealing with the determination of the samples to use to determine the age of the earth. I’c curious to see where he got these samples (just as Kevin has questioned). How do they determine that a sample is not a closed system? What is the criteria to determine this? What type of instrumentation was used to determine these U/Pb ratios? And it makes sense to use a sample that represents a whole uniformly. That’s just proper sample collection etiquette.

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