How is carbon dating done?
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In the atmosphere, cosmic rays smash into normal carbon 12 atoms in atmospheric carbon dioxideand create carbon 14 isotopes.
This process is constantly occurring, and has been for a very long time, so there is a fairly constant ratio of carbon 14 atoms to carbon 12 atoms in the atmosphere.
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Now living plants 'breathe' CO2 indiscriminately they don't care about isotopes one way or the otherand so while they are living they have the same ratio of carbon 14 in them as the atmosphere. Animals, including humans, consume plants a lot and animals that consume plantsand thus they also tend to have the same ratio of carbon 14 to carbon 12 atoms. This equilibrium persists in living organisms as long as they continue living, but when they die, they no longer 'breathe' or eat new 14 carbon isotopes Now it's fairly simple to determine how many total carbon atoms should be in a sample given its weight and chemical makeup.
And given the fact that the ratio of carbon 14 to carbon 12 in living organisms is approximately 1: In actually measuring these quantities, we take advantage of the fact that the rate of decay how many radioactive emissions occur per unit time is dependent on how many atoms there are in a sample this criteria leads to an exponential decay rate.
We have devices to measure the radioactivity of a sample, and the ratio described above translates into a rate of Voila, now you can tell how old a sample of organic matter is.
Carbon 14 dating is not great for dating things like a year old because if much less than 1 half-life has passed, barely any of the carbon 14 has decayed, and it is difficult to measure the difference in rates and know with certainty the time involved. On the other hand, if tons of half-lives have passed, there is almost none of the sample carbon 14 left, and it is really hard to measure accurately how much is left.
And last week scientists announced that new dates for an extinction event that claimed most of Australia's large animals show that humans, not the climate, wiped them out. Although visual inspection of the rocks, fossils and archaeological remains used to reconstruct our planet's past provides critical information, only by ascertaining their ages can researchers put this data into a meaningful context.
The Dating Game - Scientific American
The first step toward accurately measuring geologic time came at the turn of the 20th century, when French physicist Henry Becquerel discovered the natural radioactive decay of uranium. Shortly thereafter, building on related work by Ernest Rutherford, American chemist Bertram Borden Boltwood determined that he could use the predictable decay of radioactive elements such as uranium into other elements to keep track of time.
Although Boltwood's resulting estimates for things like the age of Earthwhich he placed at around 2. In the decades that followed, scientists made important new discoveries about the structure and behavior of atoms, and they refined their existing dating techniques.
More recently, they have developed a number of new methods.
Some use radioactive isotopes; others take advantage of different phenomena, such as thermoluminescence and electron spin resonance. Still others, like amino acid racemization, show promise but have not yet taken wing. Now, nearly years after Boltwood's groundbreaking work, it is estimated that Earth formed at least twice as long ago as he had claimed.
The following summaries offer a quick introduction to some of the dating techniques researchers have been using to explore and reconstruct our planet's past, from 4. Each isotope has what is known as a half-lifethat is, a period of time in which half of the atoms in a population decay into stable daughter elements. This half-life differs dramatically from isotope to isotope.
As a result, different isotopes are better suited to dating different items. In the case of carbon 14, for example, the half life is only 5, years.
Carbon 14 can thus reliably date items only up to around 40, years old. Other radioactive isotopes can be used to accurately date objects far older. The decay of argon 40 to argon 39, for instance, played a vital role in underscoring the significance of two ancient human skulls unearthed in the Republic of Georgia last summer.
These remains, Carl C.