List of all the dating methods
For example, dating living mollusks by the carbon-14 method often yields clearly errant results—for instance, finding the mollusks to be up to 2,300 years old (“Radiocarbon Dating: Fictitious Results With Mollusk Shells,” , Vol. Archaeologist John Mc Ray notes: “Unfortunately, several recent discoveries combine to indicate that carbon 14 is not as valuable as was once hoped: (1) radioactive carbon atoms may not have existed in the earth’s atmosphere before 2000 B.C.; (2) the natural concentration of carbon 14 in the atmosphere has varied in certain periods, and (3) there is a high probability of sample contamination” ( , 1991, p. Recently a new method—accelerator mass spectrometry—has been used to date ancient items.Isotopic dating of rocks, or the minerals in them, is based on the fact that we know the decay rates of certain unstable isotopes of elements and that these rates have been constant over geological time.It is also based on the premise that when the atoms of an element decay within a mineral or a rock, they stay there and don’t escape to the surrounding rock, water, or air.Norman Hammond of Boston University, who began digging at Cuello in the 1970s, says the remains now are believed to be from about 1200 B.
The fundamental dating assumption (‘no radiogenic argon was present when the rock formed’) is questioned by these data. Helens dacite argue that significant ‘excess argon’ was present when the lava solidified in 1986 … Helens dacite causes the more fundamental question to be asked—how accurate are K-Ar ‘ages’ from the many other phenocryst-containing lava flows worldwide?
These methods rely heavily on the assumption of uniformitarianism, i.e., natural processes have proceeded at relatively constant rates throughout the earth’s history …
It is obvious that radiometric techniques may not be the absolute dating methods that they are claimed to be.
One of the isotope pairs widely used in geology is the decay of K is a radioactive isotope of potassium that is present in very small amounts in all minerals that have potassium in them.
It has a half-life of 1.3 billion years, meaning that over a period of 1.3 Ga one-half of the Figure 8.14 The decay of 40K over time.