How to Date Fossils

Dating fossils is an interesting and enlightening process. It is a technical process that is usually undertaken by experts. The relative dating method allows you to discover whether a fossil is older or younger than another fossil or rock and the absolute dating method uses chemical testing to estimate the age of the fossils.

Method 1

Method 1 of 2:

Using Absolute Dating Methods

1
Use the carbon dating method if the fossil is less than 75,000 years old. This method only works on young fossils as carbon decays quicker than other minerals. If no traces of carbon are found in a fossil, this indicates that it is older than 100,000 years. Use an accelerator mass spectrometer to measure the amount of carbon in the fossil.^{[1]XResearch source}
- The amount of carbon in fossils decreases over time, therefore the lower the amount of carbon in a fossil, the older it is.
- Fossils need to be clean in order for carbon dating to be accurate.^{[2]XResearch source}
- This method requires specialist equipment and is usually done by experts.
2
Apply the fission tracking method. Uranium is found in many different rocks and fossils. The uranium content can cause fissures in the fossil surface. The greater the number of fissures in a rock, the older the fossil is likely to be. Use a LA-ICP-MS (Laser Ablation Inductively Coupled Plasma Mass Spectrometry) tool to measure the uranium content.^{[3]XResearch source}
- The high-tech equipment required for this technique means that it is generally only used by experts.
3
Measure the amount of argon in the surrounding rocks. Volcanic rocks can be dated by measuring the amount of argon in them. Each time a volcano erupts a new layer of ash and rock is deposited. Fossils are found in between these layers and thus can be estimated to be a similar age to the rocks that they around. Test the amount of argon using a thermal ionization mass spectrometer.^{[4]XResearch source}
- This is a technical method used by experts with access to specialized equipment.
4
Analyze the amino acid racemization. The extent of amino racemization in a fossils can be used estimate its age. The older a fossil is, the more that the amino acids will have racemized. Heat fragments of the fossils in water and then hydrolyze the fragments in 6M hydrochloric acid. This process allows you to measure the extent of the racemization process.^{[5]XResearch source}
- This method is only accurate if the humidity, temperature, and acidity conditions of the original environment of the fossil are known.
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Method 2

Method 2 of 2:

Relative Dating Methods

1
Use the stratigraphy method if the fossils were found on horizontal ground. This method only works if the fossils are not on folded or tilted ground. If you look at a cliff face made from sedimentary rocks, you will notice that there are layers of rocks. These layers are often different colours or made from different textured sediment. The oldest rocks are at the bottom and youngest are found at the top. If a fossil is found in one of the top layers, it can be assumed that it is younger than the fossils and rocks below it.^{[6]XResearch source}
- This information can be used for a variety of purposes. For example, if a human skull was found below a dinosaur bone it could indicate that humans predate dinosaurs.
2
Research where the fossil was found. If the fossil was found in a location that has a known date, this can help to identify the age of the fossil. For example, if the fossil was found inside a shipwreck from 5,000 years ago, it is safe to assume that the fossil is a similar age.^{[7]XResearch source}
- This dating method only works if a fossil is found in a location that has a known age.
3
Use index fossils to estimate the date of your fossil. Index fossils are fossils that are only found during particular time periods. If a fossil is found next to an index fossil, it can be assumed that the fossil is a similar age.^{[8]XResearch source}
- For example, brachiopod fossils are thought to be 410-420 million years old, meaning that if you found a fossil beside a brachiopod fossil it would likely be a similar age.
- If a fossil was found between an index fossil that is 410-420 million years old and an index fossil that is 415-425 million years old, you could deduct that the fossil would likely be 415-420 million years old as this is the overlapping range.
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