A zircon in a lava flow is going through radioactive decay. By the time a sample is collected by a geologist, only six percent of its original parent material still remains. How many half-lives has the zircon experienced?A. 3 half-livesB. 2 half-livesC. 5 half-livesD. 4 half-livesE. 1 half-life

All radioactive materials decay at rates that are universally known and measured in units called “half-life”. Half-life can be defined as the amount of time it takes for half of the parent atoms of any radioactive substance to decay. According to recorded studies, the following table (only 1 to 5 half lives—for convenience) shows the relationships between the numbers of half lives, the percentages of parent atoms remaining, and percentages of daughter atoms produced:

Numbers 0 1 2 3 4 5

of half

lives

passed

Percent 100 50 25 12.5 6.25 3.125

of parent

atoms

remaining

Percent 0 50 75 87.5 93.75 96.875

of daughter

atoms

produced

(Note that the actual table has results for 1, 2, 3, 4, 5, 6, 7 and 8 half lives, but due to lack of sufficient space, other results for 6, 7 and 8 half lives can't be listed in this answer.)

A close study of the above table shows that when the percentage of parent atoms is 6.25 (which is almost 6), the half life is 4.