Argon- Potassium (Ar-K) SYSTEM
K- 40 is a radioactive and decays to two different daughter products, calcium-40 and argon-40, by two different decay methods (Wiens, 2002). This is not a problem because the production ratio of these two daughter products is precisely known, and is always constant: 11.2% becomes argon-40 and 88.8% becomes calcium-40 (Wiens, 2002). It is possible to date some rocks by the potassium-calcium method, but this is not often done because it is hard to determine how much calcium was initially present (Wiens, 2002). Argon, on the other hand, is a gas. Whenever rock is melted to become magma or lava, the argon tends to escape (Wiens, 2002). Once the molten material hardens, it begins to trap the new argon produced since the …show more content…
In this way the potassium-argon clock is clearly reset when an igneous rock is formed (Wiens, 2002). One must have a way to determine how much air-argon is in the rock (Wiens, 2002). This is rather easily done because air-argon has a couple of other isotopes, the most abundant of which is argon-36 (Wiens, 2002). The ratio of argon-40 to argon-36 in air is well known, at 295 (Wiens, 2002). Thus, if one measures argon-36 as well as argon-40, one can calculate and subtract off the air-argon-40 to get an accurate age (Wiens, 2002). Although potassium-argon is one of the simplest dating methods, there are still some cases where it does not agree with other methods (Wiens, 2002). When this does happen, it is usually because the gas within bubbles in the rock is from deep underground rather than from the air (Wiens, 2002). This gas can have a higher concentration of argon-40 escaping from the melting of older rocks (Wiens, 2002). This is called parentless argon-40 because its parent potassium is not in the rock being dated, and is also not from the air (Wiens, 2002). In these slightly unusual cases, the date given by the normal potassium-argon
K- 40 is a radioactive and decays to two different daughter products, calcium-40 and argon-40, by two different decay methods (Wiens, 2002). This is not a problem because the production ratio of these two daughter products is precisely known, and is always constant: 11.2% becomes argon-40 and 88.8% becomes calcium-40 (Wiens, 2002). It is possible to date some rocks by the potassium-calcium method, but this is not often done because it is hard to determine how much calcium was initially present (Wiens, 2002). Argon, on the other hand, is a gas. Whenever rock is melted to become magma or lava, the argon tends to escape (Wiens, 2002). Once the molten material hardens, it begins to trap the new argon produced since the …show more content…
In this way the potassium-argon clock is clearly reset when an igneous rock is formed (Wiens, 2002). One must have a way to determine how much air-argon is in the rock (Wiens, 2002). This is rather easily done because air-argon has a couple of other isotopes, the most abundant of which is argon-36 (Wiens, 2002). The ratio of argon-40 to argon-36 in air is well known, at 295 (Wiens, 2002). Thus, if one measures argon-36 as well as argon-40, one can calculate and subtract off the air-argon-40 to get an accurate age (Wiens, 2002). Although potassium-argon is one of the simplest dating methods, there are still some cases where it does not agree with other methods (Wiens, 2002). When this does happen, it is usually because the gas within bubbles in the rock is from deep underground rather than from the air (Wiens, 2002). This gas can have a higher concentration of argon-40 escaping from the melting of older rocks (Wiens, 2002). This is called parentless argon-40 because its parent potassium is not in the rock being dated, and is also not from the air (Wiens, 2002). In these slightly unusual cases, the date given by the normal potassium-argon