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Recent archaeological findings have made quite specific claims about the age of the fossils or artifacts that have been unearthed – anywhere from 11,000 to tens of millions of years. Have you ever wondered just how reliable those dates really are? How, do they work the ages of these findings, and what is the margin of error? These are important questions if we want to know the truth about our past. So, lets investigate the science of ancient dating methods.
The most reliable methods of dating ancient artifacts involve the use of radioactive clocks. Radioactive clocks are superior to other methods because their rate of decay (ageing) has been shown to be unaffected by external conditions. The first such clock developed was the Uranium – lead clock which measured the rate of decay of uranium into lead. Radioactive decay follows strict laws of probability. The amount of uranium decaying in a period of time is always proportional to the amount left. The time it takes for half of the uranium to decay is called it’s half life. The half life of uranium is about 4.5 billion years. The amount of lead is increasing all the time as this is what the uranium is being converted into. The number of lead atoms is the complement of the number of uranium atoms. It is possible, then, to determine how old an item is by measuring the respective amounts uranium and iron that it contains.
This is, of course, a very simplified explanation of how the process works. There are, however, a number of pit-falls which can complicate the process. If the item is not lead free at the beginning of it’s life then it will have a built-in age which will skewer the results. Also, if uranium seeps out of the object over time, this will also affect the reading. Another element, thorium, also decays into iron, which further complicates things. To double-check these figures, then, scientists also have the potassium – argon clock and the Rubidium – Strontium clock. Both of these clocks also have inbuilt problems and sometimes there have been wildly divergent figures between the tree clocks.
To date items of less than a million years of age, scientists have the radiocarbon clock, which has a half -life of only 5,700 years. This process is also fraught with problems. One of the major ones is the fear of contamination – which can make a specimen appear older or younger than it actually is. Radiocarbon dating relies on the assumption that the level of carbon 14 in the atmosphere has always been the same as it is now. However, that rate has been shown to have increased as a result of nuclear activity and other factors over the last few decades. So, it is reasonable to assume that that rate has not remained constant over previous time.
These dating methods, then, are far from infallible. They should be treated with a degree of skepticism and should not be taken as proof absolute that previously held notions should be discarded. As with most things, it pays to have a questioning, discerning attitude when it comes to the matter of ancient dating.