Difference between relative and absolute dating methods
The technique can, however, provide the relative ages of bones from the same site.Most fossils are found in sedimentary rocks deposited in layers.
Absolute dating is not possible with this method because the rate at which the nitrogen content declines depends on the surrounding temperature, moisture, soil chemicals and bacteria.This problem is now reduced by the careful collection of samples, rigorous crosschecking and the use of newer techniques that can date minute samples.Volcanic rocks – such as tuff and basalt – can be used in dating because they are formed at a particular moment in time, during an eruption.This newer method converts a stable form of potassium (potassium-39) into argon-39.Measuring the proportions of argon-39 and argon-40 within a sample allows the age of the sample to be determined.Where the rocks are not strongly folded or tilted it is possible to work out the order in which the layers were formed.
The oldest rocks and fossils are at the bottom and the youngest are on top.
Argon is gas that gradually builds up within rocks from the decay of radioactive potassium.
It is initially formed in the molten rock that lies beneath the Earth’s crust.
Sedimentary rocks are rarely useful for dating because they are made up of bits of older rocks.
Uranium is present in many different rocks and minerals, usually in the form of uranium-238.
Knowing when a dinosaur or other animal lived is important because it helps us place them on the evolutionary family tree.