Carbon-14 has a half-life of 5,730 years. if the age of an object older than 50,000 years cannot be determined by radiocarbon dating, then * carbon-14 levels in a sample are undetectable after approximately ten half-lives. * carbon-14 levels in a sample are undetectable after approximately nine half-lives. * the half-life of carbon-14 is too long to accurately date the object. * a radioisotope with a shorter half-life should be used to date the object.