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