Evolution
Olivia Brennan
The Age of the Earth
and fossil dating
Scientists have not found a way to determine the exact age of the Earth directly from Earth rocks because Earth's oldest rocks have been recycled and destroyed by the process of plate tectonics. The age of Earth is measured by the decay of long-lived radioactive isotopes of elements that occur naturally in rocks and minerals and that decay with half lives of 700 million to more than 100 billion years to stable isotopes of other elements.
Since geologists have used the Earth's plates and rocks to estimate how old it is, scientists can use this information to discover how old fossils are. They can see that fossils from deeper in the Earth are similar to fossils that are closer. They have slight differences. This helps to support evolution. Since the fossils from long ago are similar to more recent fossils, evolution must have occurred. Scientists would not have been able to prove this if they didn't know how old the Earth and its layers are.
Scientists are also able to figure out how old a fossil is by fossil dating.
A fossil can be studied to determine what kind of organism it represents, how the organism lived, and how it was preserved. However, by itself a fossil has little meaning unless it is placed within some context. The age of the fossil must be determined so it can be compared to other fossil species from the same time period. Understanding the ages of related fossil species helps scientists piece together the evolutionary history of a group of organisms.
For example, based on the primate fossil record, scientists know that living primates evolved from fossil primates and that this evolutionary history took tens of millions of years. By comparing fossils of different primate species, scientists can examine how features changed and how primates evolved through time. However, the age of each fossil primate needs to be determined so that fossils of the same age found in different parts of the world and fossils of different ages can be compared.
There are three general approaches that allow scientists to date geological materials and discover how old the fossil is. First, the relative age of a fossil can be determined. Relative dating puts geologic events in chronological order without requiring that a specific numerical age be assigned to each event. Second, it is possible to determine the numerical age for fossils or earth materials. Numerical ages estimate the date of a geological event and can sometimes reveal quite precisely when a fossil species existed in time. Third, magnetism in rocks can be used to estimate the age of a fossil site. This method uses the orientation of the Earth's magnetic field, which has changed through time, to determine ages for fossils and rocks.
By fossil dating, and therefore discovering how old a fossil is, scientists can use their information to prove evolution. If they see that one fossil is much older than others, there may be others that are similar to it but are more or less evolved.