5 -- The Age of Our World Made Easy

With C14 dating we have to determine that the remains are not yet fossilized (no assumption) and that it was from a suitable environment for measuring (again most times there is no assumption needed). Once those are determined then we have to assume that the machine that measures the ratios of Carbon isotopes doesn't mess up, and that nobody messes up on the math. But if someone does mess up then somebody else will figure it out and fix it. That's how science works.

Very few assumptions have to be made. Pretty much the only assumptions that are made is that our measurements are correct. And they aren't always, people are human. But with science there are always multiple people doing the same measurements so if one person messes up they will get corrected. And in cases where our knowledge base isn't sufficient we eventually learn like we did with the carbon cycle with faulty results for marine ecosystems.

Very interesting. Thank you both for the answers. That will help me get started in researching and thinking about the issue.

I'm trying to figure out how much is based on reasonable data and mathematical logic, and how much is based on assumption.

Misunderstood your earlier question.

Not all life has equal ratios of carbon. Plants get it from the atmosphere and since C14 is produced from radiation from the sun hitting our atmosphere they all have very similar ratios of C14 to C12 and are datable. So are the animals that eat those plants and the animals that eat those animals. However much of the carbon in aquatic environments or very polar environments is old, so organisms from those environments can't be accurately dated using C14.

that's just a guess though.

because the regular C doesn't decay. most living things (there are some exceptions as described in the video) have roughly the same amount of C and C14, as long as they are alive. as soon as they die, the amount of C14 starts to diminish. how much it has diminished *relative* to the constant amount of C indicates how long ago it died.

I have no idea how half-lives are measured. I think it has to do with measuring the amount of energy lost over time, using E=MC^2 to translate that into matter.

@ Sahuagin

Ah, thanks. I still have some questions, if you don't mind:

* "...the amount of regular C is roughly equal to the amount of C14"

In a dead thing, how do you know how much regular C it had before it died? Do all living things have an equal amount of C-12 in them? Blindly guessing, I wouldn't think so.

Also,

C-14's half-life is projected from a few decades of observing it's decay? (I suppose that would have to be the case. Just wondering if there are any other reasons).

we can tell when something died, because the amount of regular C (that doesn't change) is roughly equal to the amount of C14 as long as an organism is alive (with some exceptions). once the organism dies, the C14 begins to decay without being replaced. using the half-life, the difference between the C and C14 present indicates how long ago it died. (IE: if C - C14 = 0, it just died; if C - C14 = C / 2, then it died ~5500 years ago; if C - C14 = 3C / 4, then it died ~11000 years ago, etc...)

it depends on the half-life or decay rate. C14 changes over time into something else, at a constant speed called a half-life. the half-life is how long it takes a certain amount of stuff to decay away half of itself. with C14 that half-life is 5500 years, so if you start with X amount of C14, after 5500 years, you have X / 2 left, and after another 5500 years, it's now X / 4, another 5500 and it's X / 8, etc..etc..

OK, but that didn't answer my question.