3 ms·

I've always been curious about how we date things so far back. It's one of those things which I wish I could understand better. Does anyone have a good resource

by vyrotek 14y ago

I've always been curious about how we date things so far back. It's one of those things which I wish I could understand better. Does anyone have a good resource on carbon dating or other modern techniques that are used today? Also, has anyone ever scientifically argued that perhaps our dating techniques are incorrect? Could there be natural ways for the system to be thrown off?

toufka 14y ago
There are of course ways to argue about the accuracy of these techniques. What's fun is that it doesn't matter which technique you use - the numbers turn up the same no matter what. That's why this 'science' thing is so cool. Measure the error rate of polymerase in lab (the protein which makes your DNA). Calculate the percent difference ("error") between humans and chimpanzees and you can get a ballpark number for the length of time it took for the species to diverge. It's astounding that these numbers end up quite similar to the numbers you get when you find bones, compare the isotope of carbon in it with the known decay rate of Carbon-14, and the ratios of it in our ecosystem. And these numbers correspond quite well between any elemental analysis we know. Have you ever told a lie? (we'll pretend you have for argument's sake) You know how quickly and difficultly it is to create a story that accords with the lie? And yet somehow telling even the most outlandish of true stories causes not even a momentary fluster? Everything just fits together. Were evolution or such things based on a single finding - then sure, be skeptical. But when evidence from a geologist, a physicist, a geneticist, a radiologist, a biophysicist, and many more all arrive at the same conclusion using wildly different techniques - then be much much less skeptical. Each user of each technique knows its error and precision. Some techniques can get you +/- a million years out to 100 million years, some +/- a decade out 1,000 years - some +/- a second out 3 days. Or for polymerase - +/- an event every .0001 seconds. But while each idea may be tenuous on its own - they all work in tandem to draw something really powerful. The most robust of these concepts span from the picosecond to 13 billion years - from the picometer to 13 billion light-years. It's fantastic. 200 years ago it was more like the millimeter to the kilometer, from the millisecond to the century.
jff 14y ago
In the case of carbon dating, plants take in carbon-14 from the atmosphere. Carbon-14 is radioactive and decays at a known rate. Once a plant dies, the carbon-14 begins to decay. By finding the ratio of carbon-14 to carbon-12 and carbon-13 in a sample, we can estimate how long it has been since the sample died. Since animals consume plants directly or indirectly, they also take in carbon-14 and can thus have their ages estimated in a similar fashion.
- ars 14y ago
  Just so you know, in practice it's considerably more complicated than that. The main limitation is that carbon dating only works to about 60,000 years (so older figures are never from carbon dating). This is well known. Less well known is that it only works if the sample has never been soaked in water. This is because the CO2 in water will dissolve into the sample completely overwhelming the original carbon ratios. This probably causes a huge number of errors in the field, unfortunately. Because how many samples have been completely shielded from water for that long? There are other datings though, but they are less accurate. Usually they are only able to date the rocks near the sample, but not the sample itself. http://en.wikipedia.org/wiki/Radiometric_dating http://en.wikipedia.org/wiki/Radiometric_dating Most commonly things are actually dated based on fossil and geological evidence, not any type of direct dating. But there is a bit of circular logic in those types of datings. First the rock is dated, and the sample is assumed to be of the same age. Next when other samples of the same type are found they are assumed to be of the same age as the first. The rock formations are then recorded and the appropriate layer is given an estimated age. Which is then used to date other things. Basically, things older than 60,000 years are dated based on what fits the theory best.
  - ericd 14y ago
    Thanks for one of those rare concentrated knowledge nuggets that are one of the best parts of HN.
  - Alex3917 14y ago
    Kind of like how we know the universe is 13 billion years old because of the speed of light. And we know the speed of light is constant because it hasn't changed in 100 years. Hmmm.
joeljonathan 14y ago
The problem with every dating method is: A) You have to assume a constant decay rate. B) You have to assume an initial quantity of whatever the "stuff" is you are measuring. C) You have to assume there wasn't anything that occurred to alter the decay rate. You can also think of it like "using an hourglass. You can use the hourglass to tell time if you know several things: the amount of sand in the top of the hourglass when it started flowing, the rate that the sand flows through the hole in the middle, and that the quantity of sand in each chamber has not been tampered with. If any of these three conditions is not accurately known, the hourglass will give an inaccurate measure of time." (That last part in quotes taken from Ken Ham's website here: http://www.answersingenesis.org/articles/ee2/dating-methods http://www.answersingenesis.org/articles/ee2/dating-methods )

by vyrotek 14y ago

toufka 14y ago

There are of course ways to argue about the accuracy of these techniques. What's fun is that it doesn't matter which technique you use - the numbers turn up the same no matter what. That's why this 'science' thing is so cool. Measure the error rate of polymerase in lab (the protein which makes your DNA). Calculate the percent difference ("error") between humans and chimpanzees and you can get a ballpark number for the length of time it took for the species to diverge. It's astounding that these numbers end up quite similar to the numbers you get when you find bones, compare the isotope of carbon in it with the known decay rate of Carbon-14, and the ratios of it in our ecosystem. And these numbers correspond quite well between any elemental analysis we know. Have you ever told a lie? (we'll pretend you have for argument's sake) You know how quickly and difficultly it is to create a story that accords with the lie? And yet somehow telling even the most outlandish of true stories causes not even a momentary fluster? Everything just fits together. Were evolution or such things based on a single finding - then sure, be skeptical. But when evidence from a geologist, a physicist, a geneticist, a radiologist, a biophysicist, and many more all arrive at the same conclusion using wildly different techniques - then be much much less skeptical. Each user of each technique knows its error and precision. Some techniques can get you +/- a million years out to 100 million years, some +/- a decade out 1,000 years - some +/- a second out 3 days. Or for polymerase - +/- an event every .0001 seconds. But while each idea may be tenuous on its own - they all work in tandem to draw something really powerful. The most robust of these concepts span from the picosecond to 13 billion years - from the picometer to 13 billion light-years. It's fantastic. 200 years ago it was more like the millimeter to the kilometer, from the millisecond to the century.

jff 14y ago

In the case of carbon dating, plants take in carbon-14 from the atmosphere. Carbon-14 is radioactive and decays at a known rate. Once a plant dies, the carbon-14 begins to decay. By finding the ratio of carbon-14 to carbon-12 and carbon-13 in a sample, we can estimate how long it has been since the sample died. Since animals consume plants directly or indirectly, they also take in carbon-14 and can thus have their ages estimated in a similar fashion.

ars 14y ago
Just so you know, in practice it's considerably more complicated than that. The main limitation is that carbon dating only works to about 60,000 years (so older figures are never from carbon dating). This is well known. Less well known is that it only works if the sample has never been soaked in water. This is because the CO2 in water will dissolve into the sample completely overwhelming the original carbon ratios. This probably causes a huge number of errors in the field, unfortunately. Because how many samples have been completely shielded from water for that long? There are other datings though, but they are less accurate. Usually they are only able to date the rocks near the sample, but not the sample itself. http://en.wikipedia.org/wiki/Radiometric_dating http://en.wikipedia.org/wiki/Radiometric_dating Most commonly things are actually dated based on fossil and geological evidence, not any type of direct dating. But there is a bit of circular logic in those types of datings. First the rock is dated, and the sample is assumed to be of the same age. Next when other samples of the same type are found they are assumed to be of the same age as the first. The rock formations are then recorded and the appropriate layer is given an estimated age. Which is then used to date other things. Basically, things older than 60,000 years are dated based on what fits the theory best.
- ericd 14y ago
  Thanks for one of those rare concentrated knowledge nuggets that are one of the best parts of HN.
- Alex3917 14y ago
  Kind of like how we know the universe is 13 billion years old because of the speed of light. And we know the speed of light is constant because it hasn't changed in 100 years. Hmmm.

joeljonathan 14y ago

The problem with every dating method is: A) You have to assume a constant decay rate. B) You have to assume an initial quantity of whatever the "stuff" is you are measuring. C) You have to assume there wasn't anything that occurred to alter the decay rate. You can also think of it like "using an hourglass. You can use the hourglass to tell time if you know several things: the amount of sand in the top of the hourglass when it started flowing, the rate that the sand flows through the hole in the middle, and that the quantity of sand in each chamber has not been tampered with. If any of these three conditions is not accurately known, the hourglass will give an inaccurate measure of time." (That last part in quotes taken from Ken Ham's website here: http://www.answersingenesis.org/articles/ee2/dating-methods http://www.answersingenesis.org/articles/ee2/dating-methods )