Absolute dating fossils

Sometimes, scientists already know the age of the fossil because fossils of the same species have been found elsewhere and it has been possible to establish accurately from those when the dinosaur lived.

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The sediment of this area was laid down after ammonite A appeared 199 million years ago, and before ammonite B became extinct 195 million years ago.

This narrows the date of the delta beds to the four million years between these dates.

Let's say you found a fossil you think to be a human skeleton.

The best radioactive element to use to date human fossils is Carbon-14.

By measuring the ratio of the amount of the original radioactive element to the daughter isotope, scientists can determine how many half-lives the element has undergone and from there can figure out the absolute age of the sample.

The half-lives of several radioactive isotopes are known and are used often to figure out the age of newly found fossils.

Index fossils are fossils that can be used to date the rock in which they are found.

The best examples are fossils of animals or plants that lived for a very short period of time and were found in a lot of places.

There are some radioactive elements in rock that decay by giving off energy and turning into different, more stable elements.

This radioactive decay takes place at a constant rate for each radioactive element.

After another half-life has passed, it will have decayed to an eighth, and so on. The half-life of potassium-40 is 1,310 million years, after which half of its substance will have changed into stable argon-40.

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