d) There are quite a few factors that need to be taken into consideration when dating an object using carbon-14 for example the origin of the object would be useful so that we can determine whether the object might have been tampered with during its time/burial, for example, in the case of the Turin shroud, scientists say that the reason the date for the shroud might be inaccurate because the cloth would have been held by human hands during its burial and the date we get might just be the dating of the flakes of skin from the hands.
Also we must use the proper equipment to extract any object as contaminated equipment might affect the results, the equipment used must be pure from any forms of radiation from previous objects as well.
When using carbon dating some geologists use the depth of the object being excavated and compare it with the dating of a different object using a different radioactive source to determine whether the dates are accurate for example, scientists could use uranium-238 to date rock samples close in depth to the carbon sample and if the two dates match, the results would be fairly accurate.
4. limitations of carbon-14 dating
Although it is a fairly accurate and effective method of dating there are some limitations to using carbon-14 dating:
The size of the sample used is important, large samples are very useful as these can be purified and cleaned to remove any outer sources of radiation, as with small samples we cannot get an accurate result as it is too small to measure.
Also, the extraction of the object has to be perfect, the object can easily get contaminated when using tools that have been affected by radiation, and also the carbon source being dated must be protected when it is extracted as it could very possibly gather some newer carbon-14 from the atmosphere around it. The packaging of the object should be made to stop any new outside radiation from reaching it as this might change the results.
Thirdly, carbon-14 dating has upper and lower limits, you cannot date very recent objects just as you cannot date objects that are too old, the upper limit is about 50000 years because after about 9 half-lives there isn’t enough carbon-14 left.
Finally, scientists use the ratio of carbon-14 to carbon-12 to determine how much carbon-14 has decayed, and it should be noted that the ratio of carbon-14 to carbon-12 has changed over time due to many man-made factors like the industrial revolution. Also, as carbon-14 is produced when cosmic rays (neutrons) from outer space hit the carbon atom and cause it to loose a proton, the recent depletion in the ozone layer might mean that the level of carbon-14 would be higher.
5. uranium-238 dating
Uranium-238 is a highly radioactive source used to date objects such as rocks. When uranium decays it slowly turns into lead, lead is not radioactive and the presence of lead in the rock would stay constant, we can then use the ratio of lead to uranium to find out how much time has passed since it was formed. E.g. the half-life of uranium-238 is about 4500 million years. So after every 4500 million years half the uranium turns into lead, if the proportion of uranium to lead in a rock is about ¼ uranium to ¾ lead then we can tell that the rock is about 9 million years old(two half-lives).
Uranium is used for dating rocks because it has a very long half-life and rocks are extremely old so it is appropriate for this kind of dating and although this method also has its limitations it is a very successful method of dating
- physics for you page 352(copy enclosed)
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