Age dating metamorphic rocks
With the exception of Carbon-14, radiometric dating is used to date either igneous or metamorphic rocks that contain radioactive elements such as uranium. Now when the uranium or thorium disintegrates, the alpha particles which are emitted are slowed down by the crystals in which the grains of the uranium- or thorium-bearing minerals are embedded.And even though various radioactive elements have been used to "date" these rocks, for the most part, the methods are basically the same. This means that if you had some pure uranium-238 with no lead in it, 4.5 billion years later one half of it would have decayed into its stable daughter product (lead-206). Where these alpha particles finally stop, crystal deformation occurs (and) shows up as a discolouration or a darkening of the crystals.Another problem that calls into question the credibility of radiometric dating is heat contamination.For example, In 1973, in Alberta, Canada (near the town of Grand Prairie) a high voltage line fell which caused nearby tree roots to fossilize almost instantly.The third assumption is that the sample has remained in a closed system.
This was first shown by Joly and Henderson who conducted most of the early studies on pleochroic haloes. We have solid evidence that radioactive decay rates cannot have been constant.Although these eruptions were less than 200 years old, the radiometric "dates" obtained from them were 140 million to 2.96 billion years for one, and from 0 to 29 million years for the other -- depending upon the (ocean) depth at which the lava sample was obtained. This also brings up an important question: If radiometric dating methods are unable to produce the correct date in cases where the actual date of eruption is known, why should we believe that these same methods can produce accurate dates when the date of eruption is unknown?The point is simply this: radiometric dating is known to produce grossly erroneous dates when heat is involved in the formation or fossilization process.In other words, the magnitude of the radius of a pleochroic halo in a particular crystal depends on the half-life of the decay responsible for the alpha particle emission. the radii of pleochroic haloes corresponding to a definite decay in a particular mineral are ...(the same) size, then it can be safely assumed that the half-life of that decay is a constant.