Carbon 14 dating assumes that the carbon dioxide on earth today has the same radioactive content as it did centuries ago. if this is true, the amount of carbon 14 absorbed by a tree that grew several centuries ago should be the same amount of carbon 14 absorbed by a tree growing today. a piece of ancient charcoal contians only 155 as much radioactive carbon as a piece of modern charcoal. how long ago was the tree burned to make the ancient charcoal if the half-life of carbon 14 is 5715 years?