!PLEASE HELP, DUE SOON! !ASAP IF YOU CAN! NUMBER 12: what mass of the radioactive isotope will be left after three(3) half-lives?

Environmental science are unconsidered with methods to preserve natural resourcesa.trueb.false

Why does the earth spin slowly, not faster? is it possible to prove it scientifically? can you prove it with math?

Which of the following is a reason why early living organisms on earth could not have survived on the surface? 1. the lack of an ozone layer 2. the lack of oxygen in the atmosphere 3. the fact that these organisms were single-celled