Luckily, we can measure these fluctuations in samples that are dated by other methods.
Tree rings can be counted and their radiocarbon content measured.
However, these "molecular clocks" are sometimes inaccurate and provide only approximate timing.
Misleading results can occur if the index fossils are incorrectly dated.
Stratigraphy and biostratigraphy can in general provide only relative dating (A was before B), which is often sufficient for studying evolution.
Radiometric dating is a technique used to date materials such as rocks or carbon, usually based on a comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, using known decay rates.
The half-life of carbon-14 is 5,730 years, so carbon dating is only relevant for dating fossils less than 60,000 years old.
If a fossil is found between two layers of rock whose ages are known, the fossil's age is thought to be between those two known ages.
Because rock sequences are not continuous, but may be broken up by faults or periods of erosion, it is difficult to match up rock beds that are not directly adjacent.Professor Willard Libby produced the first radiocarbon dates in 1949 and was later awarded the Nobel Prize for his efforts.Radiocarbon dating works by comparing the three different isotopes of carbon.There are several different methods for estimating the ages of fossils, including: Paleontologists rely on stratigraphy to date fossils.Stratigraphy is the science of understanding the strata, or layers, that form the sedimentary record.This is difficult for some time periods, however, because of the barriers involved in matching rocks of the same age across continents.