In order to Carbon date something, it must be “organic”, which means it was once living or part of something that was once living.
Before we talk about Carbon dating, we have to know a bit about radioactivity.
· All elements are at least a little bit radioactive
· Elements with more or less neutrons than normal are unstable and become more radioactive
· Living things contain an especially radioactive type of Carbon that has more neutrons than normal called Carbon-14.
· Carbon with the normal amount of neutrons is called Carbon-12 and is more stable and is also found in living things.
Radioactive material decays and becomes smaller by releasing particles and changing into other elements. One
way of measuring this decay is called the “half-life”. This is the amount of time for the radioactive substance to reduce to half its original amount.
Carbon-14 and Carbon-12 are both floating around the atmosphere. This creates a ratio of the two amounts.The ratio is always the same around the world at any point in time, but the amount of Carbon-14 in the world slowly decreases over time, because of those particles being released.
Plants get their carbon from the atmosphere and animals get their carbon from plants and other animals. Because of this, all creatures have the same Carbon-12 and Carbon-14 ratio as the atmosphere and it’s the same as the time period they lived. Once the creature dies, the amount of carbon is set. This is what’s important. All that’s left is to measure this ratio of Carbon-14 to Carbon-12. This is then compared to a table of ratios to determine the time.
In order to create this table, scientists look to tree-rings. Every tree stump has rings to indicate its age and some trees are thousands of years old. Scientists measure the amount of Carbon-14 on those old rings and create the table, so we know almost exactly how much Carbon-14 was around at that time. For example, the number associated with Carbon-14 from tree rings in the year 1200 is about 800, while for the year 1800, it’s about 200. As you can see, the amount of Carbon-14 is going down with time.