Question

WHY is carbon-14 used to date artifacts?

Answer 1

There is a very good explanation here:
https://en.wikipedia.org/wiki/Radiocarbon_dating

Answer 2

carbon 14 is used because it gives us a better idea of the age something is as compared to other substances.

this is because carbon 14 decays to around half it's value in 5700 years.

carbon-14 is constantly being produced in the upper atmosphere as cosmic particles enter or earth's atmosphere. plants absorb carbon to make sugar, and other stuff. since the life of the plant is fairly short compared to 5700 years, we usually neglect the time it takes for the plant to absorb the carbon 14.

when the plant dies, it stops absorbing carbon 14 and thus the carbon 14 starts to decay. by measuring the proportion of carbon14 and carbon in the plant/wood we estimate the age of artifects.