Charcoal (burned wood) that was used to make prehistoric drawings on cave walls in france was scraped off and analyzed. the resu
lts were 4 mg carbon-14 (parent isotope) and 60 mg nitrogen (daughter isotope). the half-life of carbon-14 is 5,730 years. how old are the cave drawings? a. 11,460 years
b. 17,190 years
c. 22,920 years
d. the sample is too old to be analyzed by carbon dating.
Half-life describes the amount of time for a radioactive substance to decay to one-half of the original substance’s weight. So, if we had 100g of C-14, after 5,730 years, only 50g remain; after another 5,730 years, only 25g would remain, and so on.
In this problem, we are meant to assume that the original amount of C-14 was 64g, and that, through decay, it forms N-14. We can figure out how many half lives have passed by figuring out how much 4 is out of 64 by dividing 64 by two repeatedly. Each time, count a half life.
64 - 32 (1 HL) - 16 (2 HL) - 8 (3 HL) - 4 (4 HL)
In this problem, 4 half lives have passed. We can now multiply this by the time for one half life to find how many years have passed.
4 x 5,730 = 22,920 years
Approximately 22,920 years have passed since the drawing was created.
The uniqueness of the plasma state is due to the importance of electric and magnetic forces that act on a plasma in addition to such forces as gravity that affect all forms of matter.
