I believe it would be to calculate the amount of C-14 atoms left. scientists began to find out how long an object has been decaying, this has to do with half lifes etc. and how long a specific mineral/elements half life is. they use this to calculate how old it is (not an exact age but it's very accurate.)
I believe this would be true
Double fertilizer in a plant
You can tell it's not a dominant trait because it would show in all the grandchildren.
Recessive
#12 is heterozygous