Potassium Argon Dating

Before there were any true scientific dating methods, scientists depended on their past archives of fossils and strata in order to determine how old a newly found fossil was. However, it wasn't until the mid 20th century that scientists could abandon this pathetic, inaccurate process and move into a more acceptable precise and detailed procedure. The old way was done by comparing one fossil to other fossils found in the same layer of the earth's ground and studying the physical characteristics of the fossil. Scientists took guesses and made assumptions of the age of a fossil and what time period in belonged to. With the discovery of chronometric dating, finally, a whole new world of answers and possibilities came into view and it opened doors to more precise and sensible answers to many questions that scientists had been asking for years.

The two types of dating are Relative Dating and Absolute Dating. Relative Dating determines the age of a fossil in relation to other fossils but doesn't give a definite, precise time; the kind of dating used before the discovery of chronometric dating. Scientists compared one fossil to another and tried to decide if that fossil was from the same time period as the original. Absolute Dating, also referred to as Chronometric Dating and Radiometric Dating, is far more accurate. It uses the Carbon content of the fossil to help determine the range of the dates that the fossil was created. Where precision is concerned, the latter of the two would be the preferred choice, obviously.

To understand Chronometric Dating one must understand that every living thing is made of Carbon [C]. When an organism dies it no longer uses this carbon, leaving an unstable isotope of Carbon which decays into Nitrogen at a pace called a "half-life". This term "half-life" is defined as: the time it takes for one-half of the atoms of a radioactive material to disintegrate. Half-lives for various isotopes can range from a few microseconds to billions of years, but the half-life for carbon (carbon 14, the form of carbon found in organisms) is five-thousand seven-hundred thirty years. In that time, half of that carbon has decayed. This technique is based upon how much carbon is left in large increments. Remains over fifty-thousand years old have very little radioactive substance left; therefore, another technique such as potassium/argon [K/Ar] dating must be used.

Potassium [K] is a radioactive substance that can be found in volcanic rock. Potassium decays into argon [Ar] gas which has a half-life of about 1.31 billion years. "Potassium either decays to calcium 40 by beta emission or to argon 40 by electron capture or positron emission" (Brown 156). This is why the Potassium to Argon ratio will increase over any amount of time and can help provide a date of fossilization.

Volcanic rocks tend to hold tightly to argon in because of their crystalline structures, and it's somewhat easy to test for the amount of argon located inside them. Working with the amount of time given by the argon in these rocks, scientists can find out how long ago the volcanic eruption occurred. This technique has proven useful in dating rocks and minerals ranging from