Question

WILL FAN AND MEDAL!

1. How is the geologic time scale organized? How do scientists define each division of time?

2. Describe how the process of radioactive decay of carbon is used to accurately date fossils.

3. How is the radioactive decay of carbon useful to scientists?

Answer 1

2. Radioactive carbon (Carbon 14) comes into existance all the time, being created in the upper part of the atmosphere, produced interactions between cosmic rays and nitrogen that is already in the upper atmosphere. The radioactiv carbon then joins oxygen molecules forming CO2 (carbon dioxide). Since plants use CO2 to complete the process of photosynthesis, plants acquire the radioactive carbon this way. As most food chains begin with a herbivore animal, and this animal gets eaten by other animals, the radioactive carbon is passed from one body to the other as part of the food chain. As soon as the animal/plant stops living, it stops interacting with the ecosystem it is a part of and and stops absorbing carbon. After death, the amount of radioactive carbon decreases in the organism until it is completely gone. This however is a VERY slow process, seeing as the half-life (a.k.a: the process within which the amount of carbon reduces to 50% of its original amount at the time of death) of C14 is ~5,730 years.

3. By detecting the amount of C14 the organism has left, one can calculate the approximate time of death of the organism.

Short version: an organism that is old as crap will have less C14 than roadkill from last week. Once all the radioactive carbon had depleted completely, other methods of testing will have to be employed.