There are several ways to figure out relative ages, that is, if one thing is older than another.For example, looking at a series of layers in the side of a cliff, the younger layers will be on top of the older layers.However, the crater number relation must be calibrated against something with a known age.To measure the passage of long periods of time, scientists take advantage of a regularity in certain unstable atoms.Thus, if we start out with 1 gram of the parent isotope, after the passage of 1 half-life there will be 0.5 gram of the parent isotope left.After the passage of two half-lives only 0.25 gram will remain, and after 3 half lives only 0.125 will remain etc.Radioactive dating is a method of dating rocks and minerals using radioactive isotopes.
The half-life is the amount of time it takes for one half of the initial amount of the parent, radioactive isotope, to decay to the daughter isotope.Most of the radioactive isotopes used for radioactive dating of rock samples have too many neutrons in the nucleus to be stable.Recall that an isotope is a particular form of an element.The only problem is that we only know the number of daughter atoms now present, and some of those may have been present prior to the start of our clock. The reason for this is that Rb has become distributed unequally through the Earth over time.We can see how do deal with this if we take a particular case. For example the amount of Rb in mantle rocks is generally low, i.e. The mantle thus has a low If these two independent dates are the same, we say they are concordant.Radiometric dating, or radioactive dating as it is sometimes called, is a method used to date rocks and other objects based on the known decay rate of radioactive isotopes.Different methods of radiometric dating can be used to estimate the age of a variety of natural and even man-made materials.Prior to 1905 the best and most accepted age of the Earth was that proposed by Lord Kelvin based on the amount of time necessary for the Earth to cool to its present temperature from a completely liquid state.Although we now recognize lots of problems with that calculation, the age of 25 my was accepted by most physicists, but considered too short by most geologists. Recognition that radioactive decay of atoms occurs in the Earth was important in two respects: Principles of Radiometric Dating Radioactive decay is described in terms of the probability that a constituent particle of the nucleus of an atom will escape through the potential (Energy) barrier which bonds them to the nucleus.Radioactive decay is a natural process and comes from the atomic nucleus becoming unstable and releasing bits and pieces.These are released as radioactive particles (there are many types).In radioactive atoms the nucleus will spontaneously change into another type of nucleus.When looking at a large number of atoms, you see that a certain fraction of them will change or dating system because you can determine accurate ages from the number of remaining radioactive atoms in a rock sample.However, rocks and other objects in nature do not give off such obvious clues about how long they have been around.