4 ms·

Carbon dating is actually only effective up to about 50,000 years, so its really only ideal for tracking human history after we started migrating out of Africa.

Carbon dating is actually only effective up to about 50,000 years, so its really only ideal for tracking human history after we started migrating out of Africa. This is because the unstable carbon-14 isotope only has a half-life of about 5700 years. There are many other forms of radiometric dating, though. Uranium-lead dating has proven relatively accurate for periods of time between 1 million to 4.5 billion years ago. Note: I'm not a geologist. I remembered that carbon was only effective for a few thousand years from a geology course I had in college, but all of this information is actually taken from articles on wikipedia: http://en.wikipedia.org/wiki/Radiometric_dating http://en.wikipedia.org/wiki/Radiometric_dating

mcrittenden 13y ago
I'm curious how it could prove accurate for that time frame? How could something like that be verified or proven?
- jmcqk6 13y ago
  Due to the way radiometric dating works, you don't need to actually verify in the way that you are using the word. However, there are at least two ways to verify the date: 1) Verify the half-life value. Radiometric dating works on the same principle: look at the ratio of pre-substance to fissioned substance. If you have a good half-life value, you can determine the age of the specimen using those values. 2) Use two different methods for getting the same age. If you use multiple, independent methods of determining the age of something, and they all come out the same, you have greatly lessened the probability that you're wrong or missed something. Of course there are ways that these can be strengthened even more using practices like double blinding the measurements.
- evan_ 13y ago
  It's all theoretical, in the same way that our understanding of gravity or radiation itself is theoretical.
  - sillysaurus 13y ago
    By that metric, our understanding of anything is theoretical.
    - evan_ 13y ago
      Yep.
  - teeja 13y ago
    It's more like a , you might get killed by a car if you step into the street kind of theoretical. Or the drip of a water clock will fill the container in 8 hours kind of theoretical. Or a don't plant too early or your people will starve kind of theoretical. A theory in science is a model backed by the huge majority of observational evidence and the collective experience of the model's community. There are no other equivalent human institutions for reliability. None. So saying "it's just a theory" in the case of uranium-dating is a fairly unreasoned attitude.
    - evan_ 13y ago
      I'm not saying it dismissively. "It's a theory" is not a negative thing to say. It does not mean that I doubt it in any way.
- jurassic 13y ago
  The best way I know to "check" radiometric ages is to date a rock using more than one isotopic system (e.g. K-Ar and U-Pb) and compare the ages that you get. If you get the same age from isotope systems with different decay rates and systematics, that is strong evidence that your technique is working. People have done this many times, and most of the error comes from different levels of uncertainty in the decay constants from one system to another. Many of the decay constants have not been updated for decades (e.g. Steiger and Jager 1977) and are suspected to be a few percent off, but the people who are qualified to make such measurements (physicists + chemists) aren't the people who want to use them in applications (geochronologists and geochemists). So the incentives aren't aligned and I doubt anyone will ever fix them. Note: Was a geology/geophysics PhD student until recently.

mcrittenden 13y ago

I'm curious how it could prove accurate for that time frame? How could something like that be verified or proven?

jmcqk6 13y ago
Due to the way radiometric dating works, you don't need to actually verify in the way that you are using the word. However, there are at least two ways to verify the date: 1) Verify the half-life value. Radiometric dating works on the same principle: look at the ratio of pre-substance to fissioned substance. If you have a good half-life value, you can determine the age of the specimen using those values. 2) Use two different methods for getting the same age. If you use multiple, independent methods of determining the age of something, and they all come out the same, you have greatly lessened the probability that you're wrong or missed something. Of course there are ways that these can be strengthened even more using practices like double blinding the measurements.
evan_ 13y ago
It's all theoretical, in the same way that our understanding of gravity or radiation itself is theoretical.
- sillysaurus 13y ago
  By that metric, our understanding of anything is theoretical.
  - evan_ 13y ago
    Yep.
- teeja 13y ago
  It's more like a , you might get killed by a car if you step into the street kind of theoretical. Or the drip of a water clock will fill the container in 8 hours kind of theoretical. Or a don't plant too early or your people will starve kind of theoretical. A theory in science is a model backed by the huge majority of observational evidence and the collective experience of the model's community. There are no other equivalent human institutions for reliability. None. So saying "it's just a theory" in the case of uranium-dating is a fairly unreasoned attitude.
  - evan_ 13y ago
    I'm not saying it dismissively. "It's a theory" is not a negative thing to say. It does not mean that I doubt it in any way.
jurassic 13y ago
The best way I know to "check" radiometric ages is to date a rock using more than one isotopic system (e.g. K-Ar and U-Pb) and compare the ages that you get. If you get the same age from isotope systems with different decay rates and systematics, that is strong evidence that your technique is working. People have done this many times, and most of the error comes from different levels of uncertainty in the decay constants from one system to another. Many of the decay constants have not been updated for decades (e.g. Steiger and Jager 1977) and are suspected to be a few percent off, but the people who are qualified to make such measurements (physicists + chemists) aren't the people who want to use them in applications (geochronologists and geochemists). So the incentives aren't aligned and I doubt anyone will ever fix them. Note: Was a geology/geophysics PhD student until recently.