Компания "ОРИОН"

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atoms with different numbers of neutrons. So each element occupies a single row, while different isotopes of that element lie in different columns. For potassium found in nature, the total neutrons plus protons can add up to 39, 40, or 41. Potassium-39 and -41 are stable, but potassium-40 is unstable, giving us the dating methods discussed above. Besides the stable potassium isotopes and potassium-40, it is possible to produce a number of other potassium isotopes, but, as shown by the half-lives of these isotopes off to the side, they decay away
rubidium-87/strontium-86 ratio on the horizontal axis, that is, it plots a ratio of the daughter isotope against a ratio of the parent isotope. At first, all the minerals lie along a horizontal line of constant strontium-87/strontium-86 ratio but with varying rubidium/strontium. As the rock starts to age, rubidium gets converted to strontium. The amount of strontium added to each mineral is proportional to the amount of rubidium present. This change is shown by the dashed arrows, the lengths of which are proportional to the rubidium/strontium ratio. The dashed arrows are slanted because the rubidium/strontium ratio is decreasing in proportion to the increase in strontium-87/strontium-86. The solid line drawn through the samples will thus progressively rotate from the horizontal to steeper and steeper slopes.
Update for 9:30 p.m. ET: University of Arizona geochemist Warren Beck got back to me with his outside perspective on the uranium-series test, and in a word, he thinks it's an "improvement" on previous methods when it comes to figuring out the age of rock art. It doesn't render radiocarbon dating totally obsolete: If you're trying to nail down the chronology of a charcoal drawing on a cave wall, carbon dating is what you want. But if you're trying to determine the age of a painting left behind in red ochre, or if you're working with paintings that go back further than, say, 40,000 to 45,000 years, "this is the way to do it," Beck told me.
account the elevation above sea level because the atmospheric shielding varies with elevation, and must also take into account latitude, as the magnetic shielding varies from the equator to the poles. Nevertheless, terrestrial cosmic-ray exposure dating has been shown to be useful in many cases.
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Dating Blogs
The uranium-234 / thorium-230 method is now being used to date animal and human bones and teeth. Previously, dating of anthropology sites had to rely on dating of geologic layers above and below the artifacts. But with improvements in this method, it is becoming possible to date the human and animal remains themselves. Work to date shows that dating of tooth enamel can be quite reliable. However, dating of bones can be more problematic, as bones are more susceptible to contamination by the surrounding soils. As with all dating, the agreement of two or more methods is highly recommended for confirmation of a measurement. If the samples are beyond the range of radiocarbon (e.g., > 40,000 years), a second method for confirmation of thorium-230 ages may need to be a non-radiometric method such as ESR or TL, mentioned below.