Outline the method for dating rocks and fossils using radioisotopes www speeddatinginthecity co uk
The Wheeler Formation has been previously dated to approximately 507 million year old, so we know the trilobite is also about 507 million years old.
But, how can we determine how old a rock formation is, if it hasn’t previously been dated?
Typically commonly occurring fossils that had a widespread geographic distribution such as brachiopods, trilobites, and ammonites work best as index fossils.
If the fossil you are trying to date occurs alongside one of these index fossils, then the fossil you are dating must fall into the age range of the index fossil. In a hypothetical example, a rock formation contains fossils of a type of brachiopod known to occur between 410 and 420 million years.
So, often layers of volcanic rocks above and below the layers containing fossils can be dated to provide a date range for the fossil containing rocks.
The atoms in some chemical elements have different forms, called isotopes.
We define the rate of this radioactive decay in half-lives.
If a radioactive isotope is said to have a half-life of 5,000 years that means after 5,000 years exactly half of it will have decayed from the parent isotope into the daughter isotopes.
Index fossils are fossils that are known to only occur within a very specific age range.This uses radioactive minerals that occur in rocks and fossils almost like a geological clock.It’s often much easier to date volcanic rocks than the fossils themselves or the sedimentary rocks they are found in. There are two main methods determining a fossils age, relative dating and absolute dating.Relative dating is used to determine a fossils approximate age by comparing it to similar rocks and fossils of known ages.