Method for relative dating
The methods are all based on radioactive decay: The first radiometric dates, generated about 1920, showed that the Earth was hundreds of millions, or billions, of years old.Since then, geologists have made many tens of thousands of radiometric age determinations, and they have refined the earlier estimates.A key point is that it is no longer necessary simply to accept one chemical determination of a rock’s age.Age estimates can be cross-tested by using different isotope pairs.It is hoped that absolute dating will be successfully implemented in the future in this region.Another way that precise dating can be achieved is if the artist records the actual date of his or her creation, the name of a leader of known reign, or a distinctive historical event, like the inscription shown in the previous chapter about King Yousif Assar Yathar’s invasion of the Najran region in 518 CE.Our understanding of the shape and pattern of the history of life depends on the accuracy of fossils and dating methods.
The discovery of means for absolute dating in the early 1900s was a huge advance.
Repeated recalibrations and retests, using ever more sophisticated techniques and equipment, cannot shift that date. With modern, extremely precise, methods, error bars are often only 1% or so.