How importent are dating methods
The earlier the age, the higher the uncertainty, due to additional causes of error.Moreover, the ages obtained by carbon-14 do not correspond to exact calendar years and thus require correction.
It is for this reason that the period corresponding to the advent of anatomically modern humans () in Europe and the transition from Neanderthal Man to modern Man remains relatively poorly secured on an absolute time scale, opening the way to all sorts of speculation and controversy.As long as it is based on dates with an accuracy of one to two thousand years and which fluctuate according to calibration curves and the technical progress of laboratories, our reasoning remains hypothetical.In such a fluctuant context, it would be illusory to place the earliest artistic parietal and portable representations from the Swabian Jura, the southwest of France, the Rhone Valley, Romania or Veneto on a relative timescale.Over time, the Ar remain embedded within the crystal, unless the rock is subjected to high temperatures after it forms.The sample must be analyzed using a very sensitive mass-spectrometer, which can detect the differences between the masses of atoms, and can therefore distinguish between Ar in the case of the K-Ar method).A clastic sedimentary rock is made up of older rock and mineral fragments, and when the rock forms it is almost certain that all of the fragments already have daughter isotopes in them.
Furthermore, in almost all cases, the fragments have come from a range of source rocks that all formed at different times.
Originally fossils only provided us with relative ages because, although early paleontologists understood biological succession, they did not know the absolute ages of the different organisms.
It was only in the early part of the 20th century, when isotopic dating methods were first applied, that it became possible to discover the absolute ages of the rocks containing fossils.
Radiocarbon dating can be used on sediments or sedimentary rocks that contain carbon, but it cannot be used on materials older than about 60 ka.
K proportion of 0.95, which is equivalent to an age of approximately 96 Ma.
One good example is granite, which normally has some potassium feldspar (Figure 8.15).