How Old is the Earth
Note that the intercepts of lines a-b-c and a'-b'-c' are identical, so the initial strontium isotopic composition can be determined from this intercept regardless of the age of the rock. I do know that there have not been too many experiments to determine what really happens to the Argon in various conditions; But there are a few. Not sure what college you want to attend yet? This is very interesting! June 10, from Answers Research Journal. The use of radiometric dating in Geology involves a very selective acceptance of data.
Quite simply, xenoliths are one of the types of rocks that cannot be dated by the K-Ar technique. This fact is readily acknowledged by Cook:. It does not work well on most metamorphic rocks because this type of rock usually has a complex history, often involving one or more heatings after initial formation. Evernden and others 43 found that these clay minerals are extremely susceptible to argon loss when heated even slightly, such as occurs when sedimentary rocks are deeply buried. However, close examination of his examples, a few of which are listed in Table 2 , shows that he misrepresents both the data and their meaning.
Talk nerdy to me! Cara Santa Maria, here. One of the ways that researchers measure the age of organic material is through carbon dating. In , Willard Libby won a Nobel Prize for developing this technology. See, all living things contain carbon, which has six protons and six neutrons, so in its typical form, we call it carbon But at any given time, there are trace amounts of carbon , or C14, in the atmosphere.
C14 is a radioactive isotope that's made when cosmic rays bombard nitrogen atoms at high altitudes, converting them to this excited form. When some living things, like plants and algae, make their own food through photosynthesis , they take in carbon dioxide from the air.
Trace amounts of C14 make up a tiny percentage of that carbon dioxide, and it's integrated into the tissues of the organism. Then creatures that can't make their own food through photosynthesis like us eat the ones that can, and that C14 is taken into our bodies as well.
And because there's a constant quantity of C14 in the atmosphere, there's a constant, corresponding quantity of it in the bodies of all living things , at least while they're still alive. That doesn't mean it's dangerous, only that it's unstable. Over time, it decays back into nitrogen.
See, when an organism dies, it stops taking in carbon. And the C14 in the organism's tissues starts to decay at a precise speed, but the amount of carbon stays the same, since it's not radioactive.
We know that it takes 5, years for half of the C14 in a sample to decay. It takes another 5, years for half of what's left to decay, and so on. This is C14's half-life. All radioactive isotopes have one. And if we compare the amount of C14 in a dead thing to the amount of regular carbon, voila! We can find out how old it is.
Now, some people who think that the earth is only 6, years old may base their claims on words in the Bible, not measurable evidence. And one ploy they use to cast doubt on radiocarbon dating is to point out its shortcomings. C14 has a relatively short half-life. So, anything older than 50, years only has too little C14 left to make an accurate calculation of its age.
But C14 isn't the only radioisotope out there. There are tons of them! If I wanted to find out the age of a dinosaur fossil , I might measure its uranium concentration, which has a half-life of million years.
However, the short half-life means it is not present in significant quantities in cooled spent nuclear fuel , unlike iodine whose half-life is nearly a billion times that of I It is discharged to the atmosphere in small quantities by some nuclear power plants.
I decays with a half-life of 8. This nuclide of iodine has 78 neutrons in its nucleus, while the only stable nuclide, I, has Iodine in food is absorbed by the body and preferentially concentrated in the thyroid where it is needed for the functioning of that gland. When I is present in high levels in the environment from radioactive fallout , it can be absorbed through contaminated food, and will also accumulate in the thyroid. As it decays, it may cause damage to the thyroid.
The primary risk from exposure to high levels of I is the chance occurrence of radiogenic thyroid cancer in later life. Other risks include the possibility of non-cancerous growths and thyroiditis. The risk of thyroid cancer in later life appears to diminish with increasing age at time of exposure.
Most risk estimates are based on studies in which radiation exposures occurred in children or teenagers. When adults are exposed, it has been difficult for epidemiologists to detect a statistically significant difference in the rates of thyroid disease above that of a similar but otherwise-unexposed group. The risk can be mitigated by taking iodine supplements, raising the total amount of iodine in the body and, therefore, reducing uptake and retention in the face and chest and lowering the relative proportion of radioactive iodine.
However, such supplements were not distributed to the population living nearest to the Chernobyl nuclear power plant after the disaster,  though they were widely distributed to children in Poland. Within the USA, the highest I fallout doses occurred during the s and early s to children having consumed fresh sources of milk contaminated as the result of above-ground testing of nuclear weapons.
The calculations are taken from data collected regarding fallout from the nuclear weapons tests conducted at the Nevada Test Site. On 27 March , the Massachusetts Department of Public Health reported that I was detected in very low concentrations in rainwater from samples collected in Massachusetts, USA, and that this likely originated from the Fukushima power plant. A common treatment method for preventing iodine exposure is by saturating the thyroid with regular, non-radioactive iodine, as an iodide or iodate salt.
Free elemental iodine should not be used for saturating the thyroid because it is a corrosive oxidant and therefore is toxic to ingest in the necessary quantities. The most common method of treatment is to give potassium iodide to those at risk. See potassium iodide for more information on prevention of radioiodine absorption by the thyroid during nuclear accident, or for nuclear medical reasons.
The FDA-approved dosing of potassium iodide for this purpose are as follows: It can also cause sialadenitis an inflammation of the salivary gland , gastrointestinal disturbances, allergic reactions and rashes.
Potassium iodide is also not recommended for those who have had an allergic reaction to iodine, and people with dermatitis herpetiformis and hypocomplementemic vasculitis, conditions that are linked to a risk of iodine sensitivity. The use of a particular "iodine tablet" used in portable water purification has also been determined as somewhat effective at reducing radioiodine uptake.
The administration of known goitrogen substances can also be used as a prophylaxis in reducing the bio-uptake of iodine, whether it be the nutritional non-radioactive iodine or radioactive iodine, radioiodine - most commonly iodine, as the body cannot discern between different iodine isotopes.
Perchlorate ions, a common water contaminant in the USA due to the aerospace industry , has been shown to reduce iodine uptake and thus is classified as a goitrogen.
Perchlorate ions are a competitive inhibitor of the process by which iodide, is actively deposited into thyroid follicular cells. Studies involving healthy adult volunteers determined that at levels above 0. Perchlorate remains very useful as a single dose application in tests measuring the discharge of radioiodide accumulated in the thyroid as a result of many different disruptions in the further metabolism of iodide in the thyroid gland. Prophylaxis with perchlorate-containing water at concentrations of 17 ppm , which corresponds to 0.
In another related study where subjects drank just 1 litre of perchlorate-containing water per day at a concentration of 10 ppm, i. However, when the average perchlorate absorption in perchlorate plant workers subjected to the highest exposure has been estimated as approximately 0.
Studies of chronically exposed workers though have thus far failed to detect any abnormalities of thyroid function, including the uptake of iodine. To completely block the uptake of iodine by the purposeful addition of perchlorate ions to a population's water supply, aiming at dosages of 0.
Perchlorate ion concentrations in a region's water supply would therefore need to be much higher, with at least a total dosage of 7. The continual addition of perchlorate to the water supply would need to continue for no less than 80—90 days, beginning immediately after the initial release of radioiodine is detected; after 80—90 days have passed, released radioactive iodine will have decayed to less than 0.
In the event of a radioiodine release, the ingestion of prophylaxis potassium iodide or iodate, if available, would rightly take precedence over perchlorate administration, and would be the first line of defense in protecting the population from a radioiodine release. The ingestion of goitrogen drugs is, much like potassium iodide , also not without its dangers, such as hypothyroidism.
In all these cases however, despite the risks, the prophylaxis benefits of intervention with iodide, iodate, or perchlorate outweigh the serious cancer risk from radioiodine bioaccumulation in regions where radioiodine has sufficiently contaminatated the environment. It is used in nuclear medicine therapeutically and can also be seen with diagnostic scanners if it has been used therapeutically.
Use of the I as iodide salt exploits the mechanism of absorption of iodine by the normal cells of the thyroid gland. Examples of its use in radiation therapy are those where tissue destruction is desired after iodine uptake by the tissue. Major uses of I include the treatment of thyrotoxicosis hyperthyroidism and some types of thyroid cancer that absorb iodine.
The I is thus used as direct radioisotope therapy to treat hyperthyroidism due to Graves' disease , and sometimes hyperactive thyroid nodules abnormally active thyroid tissue that is not malignant. The therapeutic use of radioiodine to treat hyperthyroidism from Graves' disease was first reported by Saul Hertz in The I isotope is also used as a radioactive label for certain radiopharmaceuticals that can be used for therapy, e.
In all of these therapeutic uses, I destroys tissue by short-range beta radiation. It can be seen in diagnostic scans after its use as therapy, because I is also a gamma-emitter. Because of the carcinogenicity of its beta radiation in the thyroid in small doses, I is rarely used primarily or solely for diagnosis although in the past this was more common due to this isotope's relative ease of production and low expense.
Instead the more purely gamma-emitting radioiodine iodine is used in diagnostic testing nuclear medicine scan of the thyroid. The longer half-lived iodine is also occasionally used when a longer half-life radioiodine is needed for diagnosis, and in brachytherapy treatment isotope confined in small seed-like metal capsules , where the low-energy gamma radiation without a beta component makes iodine useful. The other radioisotopes of iodine are never used in brachytherapy.
The use of I as a medical isotope has been blamed for a routine shipment of biosolids being rejected from crossing the Canada—U. Typical therapeutic doses of I are between megabecquerels MBq. Administration of this liquid form is usually by straw which is used to slowly and carefully suck up the liquid from a shielded container. Patients receiving I radioiodine treatment may be warned not to have sexual intercourse for one month or shorter, depending on dose given , and women told not to become pregnant for six months afterwards.
Such a precaution would essentially eliminate direct fetal exposure to radioactivity and markedly reduce the possibility of conception with sperm that might theoretically have been damaged by exposure to radioiodine.
Some also advise not to hug or hold children when the radiation is still high, and a one- or two- metre distance to others may be recommended. I will be eliminated from the body over the next several weeks after it is given. The majority of I will be eliminated from the human body in 3—5 days, through natural decay, and through excretion in sweat and urine.
Smaller amounts will continue to be released over the next several weeks, as the body processes thyroid hormones created with the I For this reason, it is advised to regularly clean toilets, sinks, bed sheets and clothing used by the person who received the treatment. Patients may also be advised to wear slippers or socks at all times, and avoid prolonged close contact with others.
This minimizes accidental exposure by family members, especially children. The use of chlorine bleach solutions, or cleaners that contain chlorine bleach for cleanup, are not advised, since radioactive elemental iodine gas may be released.
Patient is advised if possible to stay in a room with a bathroom connected to it to limit unintended exposure to family members. Many airports now have radiation detectors to detect the smuggling of radioactive materials that may be used in nuclear weapons manufacture.
Patients should be warned that if they travel by air, they may trigger radiation detectors at airports up to 95 days after their treatment with I. Used for the first time in to localize leaks in a drinking water supply system of Munich , Germany, iodine became one of the most commonly used gamma-emitting industrial radioactive tracers , with applications in isotope hydrology and leak detection. Since the late s, radioactive tracers have been used by the oil industry. Tagged at the surface, water is then tracked downhole, using the appropriated gamma detector, to determine flows and detect underground leaks.
I has been the most widely used tagging isotope in an aqueous solution of sodium iodide. From Wikipedia, the free encyclopedia. Iodine Complete table of nuclides.
Imsges: what is the purpose of radioactive dating
These studies suppose that cancers happen from residual tissue radiation damage caused by the I, and should appear mostly years after exposure, long after the I has decayed.
Also, if there is a partial pressure of Argon surrounding the rock, then, as experiments indicate, Argon might even enter the rock during its cooling to increase its content of Argon.
It is clear that mixing of pre-existent materials will yield a linear array of isotopic ratios. Their assumption that the fossil is the same age as the surrounding purplse allows them to do this kind of data collecting. If at some later date say, 2. March 16, from Answers Magazine. Two extensive K-Ar studies on historical lava what is the purpose of radioactive dating from radioadtive the world 3179 showed that excess argon is not a serious problem for dating lava flows. The majority of I will be eliminated from the human body in 3—5 days, through natural decay, and through excretion in funny dating advice and urine.
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