Most people realize that scientists can “date” animal or plant remains – that is, discover, approximately, when they died. \u00a0How is it done?<\/p>\n
Carbon dating is one name for the process, and it’s done by detecting the radioactivity of the dead sample. \u00a0Its radioactivity is compared to that of a living sample (perhaps surprisingly, the living sample will be more radioactive than the dead one). \u00a0From that comparison, the time of death can be approximated.<\/p>\n
The baseline radioactivity of living things is due to their constant intake of fresh carbon. Plants do so by photosynthesis; animals, by eating. \u00a0Carbon dioxide in the open air is constantly radiated by the sun. \u00a0The cosmic rays maintain a constant abundance, in the atmosphere, of about 1 radioactive carbon atom per 0.75 trillion.<\/p>\n
Once a body dies, it ceases taking in fresh carbon. \u00a0 \u00a0Therefore, the radioactive carbon in the body is no longer replenished. \u00a0It\u00a0constantly decays with a half life of 5730 years <\/strong>– which means that, every 5730 years, only half of the radioactive carbon remains compared to previously.<\/p>\n From the table, if a specimen retains about 3% radioactivity relative to a living sample, it’s around 5 half lives old, or 5(5730)= 28650 years old.<\/p>\n What if the sample retains a percentage radiation not on the table, like 60% or 35%? The math for such cases will be covered next post:)<\/p>\n Source: Ken Sejkora<\/a><\/p>\n\n
\n number of half lives elapsed<\/td>\n 0<\/td>\n 1<\/td>\n 2<\/td>\n 3<\/td>\n 4<\/td>\n 5<\/tr>\n \n % radioactive carbon remaining<\/td>\n 100<\/td>\n 50<\/td>\n 25<\/td>\n 12.5<\/td>\n 6.25<\/td>\n 3.125<\/td>\n<\/tr>\n<\/table>\n