What are the benefits and disadvantages of radiometric dating
Pro The half life of radioactive substances are empirically determined. The ratio of the parent to daughter atoms can be used to determine an exact age given the assumptions that none of the original parent atoms have been eroded or lost during the time being calculated. Con All radioactive dating except Carbon 14 are based on atoms found in igneous rocks.
Fossils are almost never found in igneous rocks.
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- What are the pros and cons of radioactive dating?.
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- The Disadvantages - Radiocarbon Dating.
So radioactive dating can not be used to directly date fossils. The one exception is Carbon However Carbon 14 has a relatively short half life so it cannot be used on fossils much older than 50, years which makes it useful for anthropology but not geo history. Also most fossils no longer contain Carbon they have been turned to stone.
Some examples include charcoal, bone, shells, leather, and even paper. These samples are dated by comparing the ratio of 14C atoms to 12C atoms. Things that were non-living such as rocks or extremely old carbon-based compounds such as fossil fuels cannot be dated. In the late 's and early 's researchers studying US bristle cone pine and German and Irish oaks discovered fluctuations in the C14 concentration. Measurements of the Libby half-life showed that Libby was about. We cannot be certain of the exact year in which a sample came from: Research of tree rings has revealed that the amount of radiocarbon has not been constant.
Because of this dating a relatively young sample is very difficult. This has been a trade off, however, because scientists were able to track radiocarbon through the environment and learn about the transportation of radiocarbon. Here is a table of calibrated ranges for samples from to BC. As you can see, the range is quite substantial for some calendar years. There are several methods to radio carbon dating. They include the gas counting method of the 's, liquid scintillation counting, and accelerator mass spectrometry.
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In the 's, it was found that certain organic compounds emit light when exposed to radiation. A fluorescence event is proportional to the decay event of C14; and the frequency is proportional to the number of C14 atoms in the sample. This forms lithium carbide. The lithium carbide is heated to o C and placed under a vacuum for 30 minutes to remove un-reacted gasses and complete the synthesis.
Then using a catalyst such as silica-aluminum vandium activated catalyst benzene is formed. The benzene is separated from the catalyst and stored in refrigeration to await counting. The benzene is transferred into counting vials that contain the sample solvent and scintillation.
The sample is transferred to a Quantulus spectrometer. There it is cooled and adapts to the dark for eight hours. Then the counting begins. The sample is converted into a beam of ions whose mass is measured by the addition of magnetic and electric fields. Because the concentration of C14 is so minute, it is difficult to use conventional mass spectrometry. The technique gave 90 million years, but took no account of the non-constant erosion rate, or the loss and recycling of salt, or the fact that salt is obtained from other sources as well as continents.
More recently, work has been done on ocean sediments [S. Nevins, Institute for Creation Research]. This suggests that, given the current annual rates of erosion some Clearly, this seems incompatible with an ocean billions of years old. However, this may be a simplistic computation since there is Sediment Recycling as sediments accumulate and cause continental plates to collide, resulting in land uplift and subsequent errosion. The Earth's magnetic field is thought to arise from circulating electic currents in the Earth's molten metalic core, and scientists agree that the field is weakening.
At the current rate of decline it could take just 1, years to disappear, with increasing effects upon the electronic systems of satellites and spacecraft. Magnetic field decrease applies to other planets. For instance, recent satellite measurements show that Mercury's magnetic field is rapidly decaying and YE Creationists claim this indicates a young field.
OE scientists believe that a weakened magnetic field could herald a new magnetic pole reversal. Magnetic pole reversals are rebutted by YE creationists. Instead they claim that the field decrease can be used as a clock to date the earth since it has been decaying since the origin of the earth. Taking the half-life of the decaying magnetic moment at years , the field is now only about one third as strong as it was at the time of Christ. Working further back in time, the value of the earth's magnetic field approaches that of a magnetic star at 10, years ago.
Since this would need a huge nuclear power source, it seems magnetic field decay places an upper age limit on the earth of the order of 10, years.
The Age of the Earth
Whilst the rigour of this YE theory is disputed see talkorigins , recent spacecraft observations have confirmed its planetary magnetic predicions made in ! The decay of uranium and thorium isotopes results in a net build-up of Helium-4 atoms in the atmosphere. It is claimed to be increasing at an annual rate of 3. From these figures and known decay rates, it can be shown that the current amount of atmospheric Helium can be generated in just 11, years not billions of years. Short-period comets orbit the sun in less than years the Halley comet orbits about every 76 years.
Each time they come close to the sun they lose material the comet tail and disintegrate.
Age of the Earth: strengths and weaknesses of dating methods
If no new comets are being generated , it would appear that no short-period comets can survive more than about 10, years - implying a young earth. This claim is countered by the fact that the origin of short-period comets is still uncertain and that there may be a source of short-period comets e. This is perhaps one of the more challenging anomalies for OE science.
It is claimed that Homo sapiens appeared some , to , years ago. But doesn't it seem strange that after more than , years earth's population is still only 7 billion? After all, the population increased from 1 billion in to 7 billion in - a span of just years! Of course, population growth is exponential, but even then the numbers don't add up.
Some claim a world-wide catastrophe may have occurred around 70, years ago, reducing the human population to maybe just 1, breeding pairs. Let's do the maths on these 'catastrophe' figures. Of course, there are many factors that affect r, such as climate, disease, war, standard of living and so on. Typically, population growth rates are between 0. In words, earth's population should be some million, billion, billion, billion. This an impossibly large number when compared to the earth's current 7 billion people. Either the population growth calculation is hopelessly wrong, or the theory of human evolution is suspect!
This computation appears much more realistic.
Earth dating via ocean sediments, magnetic field decay, atmospheric helium, short-period comets and other techniques point to a young earth. However, the scientifc accuracy of YE claims are frequently challenged e. In order to balance the discussion we should also challenge the currently accepted radiometric dating methods.
If these are suspect then the disputed methods take on more meaning.
There are several causes for concern here. The K-Ar method dates rocks by measuring the accumulated Ar It is claimed the advantage of this method is that it circumvents the zero date problem i. In other words, all Ar in a rock is assumed to have been produced by in-situ radioactive decay of K within the rock since it formed and there was zero Ar in the rock when it solidified.
However, this primary assumption has been challenged e. This 'zero Ar' problem has also been identified by Snelling who comments for one research project:. Certainly it is known to diffuse easily from deeper rocks under pressure so surface rocks tend to have a higher Ar concentration than would be expected. This, coupled with the fact that potassium is easily washed out of minerals, suggests this technique can give an artificially high age for the earth and leads some to conclude that:. If we question these techniques, there is an alternative method called isochron dating.