For living things, we do have a radioactive isotope that we can measure.It's called carbon-14 and is created by cosmic ray neutrons striking nitrogen atoms in the atmosphere.Favoriting this resource allows you to save it in the “My Resources” tab of your account.
It's based on the very simple principle that radioactive isotopes decay at a steady, predictable rate.
Radium, for example, has a half-life of about 1,600 years.
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.
For example, if fossils of B date to X million years ago and the calculated "family tree" says A was an ancestor of B, then A must have evolved earlier.
It is also possible to estimate how long ago two living branches of a family tree diverged by assuming that DNA mutations accumulate at a constant rate.
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.
If you know how pure your block of radium originally was, it's relatively simple to calculate how old it is by measuring how much radium is left.
This is a very useful tool if you have solid blocks of radium that need dating, but if you don't know how much radium was there in the first place, the job is a lot harder.
That is, if you had a solid block of radium, half of it would decay into other elements in 1,600 years.