How ancient items are dated?

Answer 1

There are a number of different techniques utilised by archaeologists to date items, be they ancient or more modern. The method most well-known outside academia is radiocarbon dating, also known as carbon-14 dating or merely carbon dating. Carbon-14 is a radioisotope found within all living things. Once an organism dies, the carbon-14 decays exponentially; so by measuring the levels in a sample, the death of an organism can be dated with reasonable accuracy.

Dendrochronology is another well-known technique, used to date the felling of timber. Over the years, humankind has amassed a vast amount of data on weather patterns, volcanic eruptions and other events that cause noticeable effects in tree rings (the rings that can be seen in the trunk of a felled tree). This allows us to establish the precise date that a tree was felled. However, it is not necessarily an accurate method of dating a building or other construction, since old timbers are frequently re-used in new buildings.

There are several other methods including radiometric dating (similar to radiocarbon dating but uses other isotopes instead of carbon-14) such as rhenium-osmium dating, uranium-thorium dating and potassium-argon dating; fluorine absorption dating (which allows archaeologists to establish how long an item has been in the soil); thermoluminescence dating (which establishes the elapsed time since a crystalline structure - ie; a ceramic - was heated, allowing archaeologists to estimate when a clay pot was fired in a kiln) and a number of more limited methods such as astronomical chronology (used to date objects relating to known astronomical events); paint analysis (which dates an item according to the chemical composition of paint used on it) and amino acid dating, used to date organic samples.

Finally, many items will fit into categories of objects that have already been dated. For example, if you were to excavate a red pot with pictures of eagles on it in Athens and you already know that red pots with pictures of eagles were the height of fashion in Athens circa 1500 BCE (BC), there is a high likelihood that your put dates from that period. Contrary to what many people believe, archaeologists are not merely treasure-hunters or people who spend their lives digging stuff up - a very large amount of their time is spent either meticulously recording fine details of their discoveries to allow this dating method to be used, whereas others spend their days in laboratories using the scientific dating methods outlined above.