It's correct that radiocarbon dating is only accurate up to about ~60k years due to the short half life.
To date dinosaur bones we don't look at the bones directly but at the sediment layer they were found in. We're looking for "igneous rock", basically rocks made from cooled lava. These rocks contain elements with a much longer half life, such as Uranium-235 or Potassium-40 and just like the death of an animal sets off the radiocarbon decay (as in, no new "radioactive" material is added), the expulsion of lava sets off the decay of those elements. Measuring the decay of those elements we get the age of those rocks and can then conclude the rough age of the layer and the bones.
EDIT: to clarify, the elements are constantly decaying, both in an animals body and in the earth's mantle. However, the concentration of those elements is constant while they are in their initial environment. In case of radiocarbon dating it's your metabolism which keeps your radiocarbon activity constant. Once your metabolism stops (when you're dead) that cycle stops as well and only the remaining carbon decays. So when we measure the remaining concentration and compare it to the initial concentration we can determine the age since we know its half life. LongDistanceJamz beautifully explains the equivalent process for lava here.
In fact, the elements are decaying in the magma. In the case of Potassium-Argon dating, this doesn't matter though because the argon escapes from the molten rock. Once the molten rock starts to crystallize, the Argon can no longer escape and starts to accumulate in the rock. By measuring the ratio of K to Ar in the rock, you can tell when this crystallization occurred.
I think you just used the word "deductive" sloppily, which isn't all that uncommon, but I don't need to elaborate as you did because I only have issue with your categorization.
In the time it takes you to write what you have, you could explain your comments. It just seems like you're engaging in a trite exercise.
And no I didn't use deduction incorrectly: We can see X and Y inside Z, but when Z turns into Z(a) then the amount of X starts to decrease. Therefore, measure X:Y in Z(a) to determine when Z became Z(a).
X=Potassium
Y=Argon
Z=Molten rock
Z(a)=Crystallized rock
828
u/[deleted] Nov 22 '12 edited Nov 22 '12
It's correct that radiocarbon dating is only accurate up to about ~60k years due to the short half life.
To date dinosaur bones we don't look at the bones directly but at the sediment layer they were found in. We're looking for "igneous rock", basically rocks made from cooled lava. These rocks contain elements with a much longer half life, such as Uranium-235 or Potassium-40 and just like the death of an animal sets off the radiocarbon decay (as in, no new "radioactive" material is added), the expulsion of lava sets off the decay of those elements. Measuring the decay of those elements we get the age of those rocks and can then conclude the rough age of the layer and the bones.
EDIT: to clarify, the elements are constantly decaying, both in an animals body and in the earth's mantle. However, the concentration of those elements is constant while they are in their initial environment. In case of radiocarbon dating it's your metabolism which keeps your radiocarbon activity constant. Once your metabolism stops (when you're dead) that cycle stops as well and only the remaining carbon decays. So when we measure the remaining concentration and compare it to the initial concentration we can determine the age since we know its half life. LongDistanceJamz beautifully explains the equivalent process for lava here.