What are two ways of dating fossils
Because we know how many kinds of rocks form volcanically, and we also know that they contain ratios of elements that change at a known rate (because some elements undergo radioactive decay at a known rate), we can compute the approximate age of the rocks, and thus the fossils. Index fossils: There are certain species of organisms that we find unique to certain layers of soil of a certain age (as determined by #1).
Despite seeming like a relatively stable place, the Earth's surface has changed dramatically over the past 4.6 billion years.
A common problem with any dating method is that a sample may be contaminated with older or younger material and give a false age.
This problem is now reduced by the careful collection of samples, rigorous crosschecking and the use of newer techniques that can date minute samples.
The majority of the time fossils are dated using relative dating techniques.
Using relative dating the fossil is compared to something for which an age is already known.