Scientists use dating techniques to find out the age of archaeological finds. There are many types of dating techniques, including natural dating techniques, electromagnetic dating techniques, chemical dating techniques and radiometric dating techniques.
One of the oldest dating techniques is geochronology. This method is based on the idea that objects layered on top of of other objects are likely from a more recent date. In this way, once a scientist determines the absolute age of a geologic formation, they can then approximate indirect dates for the layer of soil or objects in a particular layer.
One of the most well-known examples of electromagnetic dating is called archeomagnetism. This dating technique is based around the idea that the Earth's magnetic field shifts over time. Objects that have a sufficient amount of iron can be tested to see how their magnetic characteristics reflect in comparison to these magnetic shifts, and this technique has been used to date objects as far back as 5,000 years.
There are many chemical dating techniques used by scientists. One of them is known as obsidian hydration (rind) dating. Objects from volcanoes are commonly encased in obsidian. When obsidian is in water for a long period of time, it erodes at a common rate, especially if the water's temperature stays fairly constant over a long period of time. Using these factors, scientists have been known to date objects as far back as 200,000 years.
There are also many radiometric dating techniques, such Carbon-14 dating, which is based around the idea that unstable radioactive elements such as Carbon-14 (as well as potassium-argon and thorium-230) decay at a known rate over time. This allows scientists to age objects based on their amount of atomic decay.