Scientists can determine the age of ancient objects by a method called radiocarbon dating. The bombardment of the upper atmosphere by cosmic rays converts bitrogen to a radioactive isotope of carbon, C-14, with a half life of about 5730 years. Vegetation absorbs carbon dioxide through the atmosphere and animal life assimilates C-14 through food chains. When a plant or animal dies it stops replacing its carbon and the amount of C-14 begins to decrease through radioactive decay. Therefore, the level of radioactivity must also exponentially decay. A parchment fragment was discovered that had about 74% as much C-14 radioactivity as does plant material on the earth today. Estimate the age of the parchment.