Radiometric dating metamorphic rocks


16-Apr-2020 10:48

radiometric dating metamorphic rocks-29

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We can also construct a Concordia diagram, which shows the values of Pb isotopes that would give concordant dates.The Concordia curve can be calculated by defining the following: ).U leakage would cause discordant points to plot above the cocordia. Lunar rocks also lie on the Geochron, at least suggesting that the moon formed at the same time as meteorites. Pb separated from continents and thus from average crust also plots on the Geochron, and thus suggests that the Earth formed at the same time as the meteorites and moon.But, again, exptrapolation of the discordia back to the two points where it intersects the Concordia, would give two ages - t* representing the possible metamorphic event and t and solve for t . This argument tells when the elements were formed that make up the Earth, but does not really give us the age of the Earth. Thus, our best estimate of the age of the Earth is 4.55 billion years.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.Nd ratios on several minerals with a mass spectrometer and then from the slope determine the age of the rock. If a magma cools quickly on the surface of the Earth, some of the Ar may be trapped.

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.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.The method compares the abundance of a naturally occurring radioactive isotope within the material to the abundance of its decay products, which form at a known constant rate of decay.

and is now the principal source of information about the absolute age of rocks and other geological features, including the age of fossilized life forms or the age of the Earth itself, and can also be used to date a wide range of natural and man-made materials.

Additionally, elements may exist in different isotopes, with each isotope of an element differing in the number of neutrons in the nucleus.



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