As seen in the tables above, there are three isotopes of uranium. Of these, U is by far the most abundant Radioactive elements tend to become concentrated in the residual melt that forms during the crystallization of igneous rocks. Radioactive isotopes don't tell much about the age of sedimentary rocks or fossils. The radioactive minerals in sedimentary rocks are derived from the weathering of igneous rocks. If the sedimentary rock were dated, the age date would be the time of cooling of the magma that formed the igneous rock.
The date would not tell anything about when the sedimentary rock formed. To date a sedimentary rock, it is necessary to isolate a few unusual minerals if present which formed on the seafloor as the rock was cemented.
Glauconite is a good example. Glauconite contains potassium, so it can be dated using the potassium-argon technique. How does Carbon dating work? Cosmic rays from the sun strike Nitrogen 14 atoms in the atmosphere and cause them to turn into radioactive Carbon 14, which combines with oxygen to form radioactive carbon dioxide.
Living things are in equilibrium with the atmosphere, and the radioactive carbon dioxide is absorbed and used by plants. The radioactive carbon dioxide gets into the food chain and the carbon cycle. All living things contain a constant ratio of Carbon 14 to Carbon At death, Carbon 14 exchange ceases and any Carbon 14 in the tissues of the organism begins to decay to Nitrogen 14, and is not replenished by new C The change in the Carbon 14 to Carbon 12 ratio is the basis for dating.
The half-life is so short years that this method can only be used on materials less than 70, years old. Archaeological dating uses this method. Also useful for dating the Pleistocene Epoch Ice Ages.
Assumes that the rate of Carbon 14 production and hence the amount of cosmic rays striking the Earth has been constant through the past 70, years. These trails are due to the spontaneous fission of uranium. Enlarge tracks by etching in acid so that they may be visible with light microscope See readily with electron microscope Count the etched tracks or note track density in an area Useful in dating: Micas up to 50, tracks per cm squared Tektites Natural and synthetic manmade glass Reheating "anneals" or heals the tracks.
The number of tracks per unit area is a function of age and uranium concentration.