How long is radioactive carbon dating approx. useful for?
443590
Check this site: http://www.et.byu.edu/~adw45/Carbon%20Dating.htm\nIt's an undergrad paper that won "undergrad paper of the year" according to the website.  Second paragraph states, "...carbon dating can only be use to date geologically young, 35k - 50k years, carbon containing substances..."\n\nWikipedia's article on carbon dating says "The current maximum radiocarbon age limit lies in the range between 58,000 and 62,000 years. This limit is encountered when the radioactivity of the residual 14C in a sample is too low to be distinguished from the background radiation."
525263
Most of what people examine when they look at earth history is the different life forms that occurred in the past.\n\nHowever, there is more to earth history than just fossils. We just need to look at things that are inorganic rather than organic in nature.\n\nStratigraphy is one way to examine earth's history. We can look at the way sedimentary rock has been deposited to tell alot about former environments. We can find out about transgressions & regressions of the oceans & other changes in sedimentary environments.\n\nOxygen isotopes can be used to determine past climates. Speleothems are analyzed for the oxygen isotopes. They are usually looking for heavy isotopes of oxygen. Heavier isotopes of oxygen tend to get locked up in ice sooner than "normal" oxygen. So if a speleothem has less heavy oxygen then we know the sea level was probably lower due to it being "locked up" in the icecaps. This would tell us a lot about how much the sea has risen & how much of the polar ice caps had melted, etc. By the way, speleothems are cave deposits usually referred to as stalactites & stalagmites.\n\nWe can also look at ice cores from Antarctica & the Arctic. They are also examined for isotopes of oxygen.\n\nWe can look at tree rings for not too distant reaches into the past.\n\nVarves are subtle layers that have been laid down at the bottom of lakes or ponds that show changes in environment. This works much like tree rings.\n\nCores from the ocean floor are also used & works in much the same way as varves except on a larger scale.\n\nAs far as radiocarbon dating goes, it is only useful on things that were once living b/c all living things build up carbon as they live. When they die, these radioactive carbon isotopes begin to break down steadily over time.\n\nHowever, there are other radioactive isotopes that can be used to find out the ages of rocks. It works on the same principle as radiocarbon dating; radioactive isotopes break down at a constant & steady rate which soley depends on their half-life of that particular isotope.\n\nSome of the other radiometric isotopes used to date rocks are: Potassium/Argon & Uranium/Lead
776734
It's called radio-carbon dating.\nhttp://en.wikipedia.org/wiki/Radio-carbon_dating
582505
haha, you're looking into the intelligent design debate hey?\n\nRadioactive elements are materials which decay over time into other elements. Carbon 14+ is such an element. Overtime it decays into other forms of Carbon, like Carbon 12+ I think. Scientists know exactly how long it takes for half of a Carbon 14+ to decay through doing experiments. This is known as its "half life". \n\nPlants and animal produce small quanitities of Carbon 14+. Once they die, the Carbon 14+ in their bodies is no longer replenished and begins to decay. By analysing the amount of Carbon 14+ left in a body, you can tell how long ago it died to within a few thousand years. \n\nFor example if the half life of carbon 14+ was 10,000 years (I don't know the exact value), and a fossil had one quarter of the Carbon 14+ of a living body, you know it died roughly 20,000 years ago.\n\nThe bible's great mate, but it's no substitute for science.
88025
Carbon 14 has a half life between 5700 and 5730 years.\n\nSo if you have 100 unit, in 5730 years you would then have 50 units, in another 5700 years you would have 25 units.\n\nIn yourcase, your tree is 11,000 years old. So the original proportion would be 100% and in 11,000 years it would halve once and nearly a second time, so you would be left with about 28% or roughly 1/4 like the first answer said.\n\nhttp://hypertextbook.com/facts/1997/MargaretKong.shtml
66333
Earth is way older than radiocarbon dating can determine, i.e. way older than 60,000 years.\n\nSedimental rocks show evidence of the magnetic cycles of earth which reach back into the pre-cambrium.\n\nThorium decay is used for dating ancient rocks, and Thorium decay has been put into relation with these cycles. While not perfect, this method has so far given good evidence.
168747
In radioactivity, it is the time taken for half of the nuclei in a given sample to decay (either by alpha or beta decay).  These vary form radioisotope to another.  For example Carbon-14 has a half life of 5700 years.  This means that if I have 1 gram of carbon-14, 5,700 years from now I will end up with 0.5grams (the rest would have become Nitrogen with beta decay).  If another 5,700 years pass I end up with 0.25g (!) and not 0g as common sense would indicate.  Each time a half life passes HALF the nuclei decay!In fact 'activity' decreases as time passes.\nAs said this time interval varies a lot.  The half life of Uranium-238 is 4,470,000,000 years, while that of thorium-230 is only 75,380 years.  Other half lives are quite short.  E.g. Iodine-131 has a half life of just 8 days and Sodium-24 has a half life of just 15 hours!
874077
You have asked this question in different forms elsewhere -- I am not sure what you mean by "period and sign dating" here so I will assume you mean dating of fossil remains in general.\n\nMy most detailed answer is located in response to this question:\n\nhttp://answers.yahoo.com/question/index;_ylt=AlreU4PXgsD7aQCLe3GmF4Psy6IX?qid=20061115131041AAnjMF1\n\nTo sum up:\n\nThe world's carbon consists mainly of the Carbon-12 and Carbon-13 isotopes, which are not radioactive and are therefore stable, and a small amount of Carbon-14 which is a radioactive isotope of Carbon and is not stable (it decays over time, turning into stable Nitrogen at a very regular and slow rate).\n\nThe rate at which Carbon-14 decays into Nitrogen and the rate at which new Carbon-14 is created by the action of solar radiation on the upper atmosphere are essentially identical.  This, the ratio of Carbon-14 to Carbon-12 on the earth is fairly stable as a whole.\n\nLiving things take in carbon as part of their life cycle.  As long as they are alive, carbon is coming into and going out of their systems continuously, so it is being maintained at essentially the same ratio of Carbon-14 to Carbon-12 as the world at large.\n\nWhen something dies, the intake of carbon stops.  As the radioactive carbon-14 breaks down into Nitrogen, it is not replaced with new Carbon-14.  In time essentially ALL of the Carbon-14 will decay into Nitrogen, but until then the ratio of Carbon-14 to Carbon-12 (Carbon-14 divided by Carbon-12) will give a fairly accurate representation of how long the thing has been dead, assuming it has not been contaminated with fresh Carbon.\n\nSince geological dating is mainly concerned with rocks, there are 2 things preventing carbon-14 from being used:  (1) the rocks were not living things taking in carbon from their surroundings, so we can't say WHAT their original ratio of Carbon-14 divided by Carbon-12 was, and (2) rocks are so old that even if they HAD started with the normal ratio of Carbon-14 to Carbon-12, all of that Carbon-14 would have long since decayed into Nitrogen -- there would not be enough left to be able to measure it.
476885
Carbon-14: Archaeological dating\nAmericium-241: Smoke detectors\nCobalt-60: Food Irradiation\nPhosphorus-32: Biology study
14216
Know-it-all... is wrong.\nBeing radioactive, carbon-14 eventually decays to form nitrogen-14 and a  beta particle (high speed electron). \nThe process is called beta decay.\nThe HowStuffWorks link explains it adequately
181093
Archaeologists use the term BP to mean "years Before the Present", which avoids the whole philosophical debate about AD and BC versus CE and BCE. The only trouble is, the Present, of course, changes every year. Since the BP designation was at least originally associated with radiocarbon dating, archaeologists chose the year 1950 as 'the present'. Radiocarbon dating was invented in the late 1940s, and, also, atmospheric nuclear testing was begun in the 1940s, which makes, at least the theory goes, radiocarbon dates after 1950 virtually useless, anyway. \n\nGenerally CE (for Common Era or AD) and BCE (for Before the Common Era or BC) are more acceptable.
75199
well, you are right.  the validity of radiocarbon dating depends on the assumption that the half-life of carbon-14 isotopes does not change with time.\n\nbut, one of the principles of most use in scientific investigations is occam's razor, which says that when presented with a choice, usually the simplest answer is the most correct.  so, it is -assumed- that the half-life was not different a thousand years ago.  however, it is possible.  \n\nbut radiocarbon dates have been validated by other methods (such as counting rings on big trees, for instance) and there is no evidence for any change in the half-life of carbon in the time that the method has been in use.  also, a time-invariant half-life fits in with the current understanding of nuclear decays, so it seems pretty unlikely that it would change over time.\n\nas for the moon, it is not a candidate for carbon dating, which only works on samples that were alive at some point - bones, trees, antlers etc.  the basic idea is that the living organism exchanges carbon with the environment while it's alive, and stops doing so when it dies.  since the proportion of radioactive carbon in the environment is fixed, then when the organism dies, it's decaying carbon-14 content stops being replenished by eating, breathing etc.  so since the moon is mostly rock, and no biological processes exist (that we know of) on the moon, carbon dating doesn't work there.\n\nso anyway, in general i agree that everyone should be a skeptic.  nobody should blindly accept something just because they are told "it is so" but should try to understand the whys and hows and come to understand it themselves!  these days science is treated with almost as much reverence as religion once was.  \n\nlong ago, if the pope said something was so, it was so - and now, if a scientist says something is so, people accept it as so!  unfortunately this is just one of the fundamental problems of human nature - we often accept what we are told because it's told to us by an authority.   so it makes me happy when someone asks questions that challenge the assumptions!
650039
what a troubling Q: but i agree with that 6k yrs of this planet... the carbon dating is nothing but a paleontological gibberish... the world is not a million or so yrs old... mybe they just need a lil more tyme checking the computations... one million yr wud mean a day or a week in the christian "dating" watdayathink?? (,"}
941865
It is quite reliable when properly applied.  It can't be trusted when:\n\n(1) it is applied so far in the past that it is extreme extrapolation of limited data.\n\n(2) the sample and its food source were radiation-protected.\n\n(3) the sample came from a situation or time where the C14/C12 ratio was different from what it is today, or is unknown.\n\nFor all these reasons, the farther back in time you try to read, the less reliable the dating.
153391
I'm assuming that that refers to giving the age of two things relative to one another, rather than identifying the absolute ages of things.  For instance, when you take two trees that lived in similar times and places, you can look at the width of the tree rings to get an idea as to the conditions (especially moisture) during a given year.  If you have two such wood samples, you should be able to see a pattern between the two.  Using taht information, you could count rings and figure out how much older one piece of wood was relative to the other.  But without knowing the year the trees dies, or without knowing the particular calendar years behind the droughts, you wouldn't know that absolute age of either.  I'd imagine that there are similar things with radioisotope dating if you have a reason to think that the atmospheric conditions creating certain isotopes might change, but not knowing the exact concentrations at the time an organism lived.
221300
Measured by the decay of long-lived radioactive isotopes of elements that occur naturally in rocks and minerals and that decay with half lives of 700 million to more than 100 billion years to stable isotopes of other elements, scientists believe that the age of the earth is approximately 4.4 to 4.6 billion years old.
664667
All fossils should have some Carbon-14, but hypothetically, if one didn't, a different radioactive isotope could be used to determine the age of a fossil.