Answer: the basaltic, andesitic, and rhyolitc
The correct answer is: Alfred Wegener. Alfred Wegener (1880-1930) was a German polar researcher, meteorologist and geophysicist, and a first person who suggested that the continents were once a supercontinent called Pangaea, but slowly drifted apart. While he was still alive, Wegener was best-known for his achievements in <span>meteorology and as a pioneer of polar research, but today he is most remembered as the creator of the theory of the continental drift. This idea was controversial in the beginning, but today, scientist believe that Pangaea really existed during the late Paleozoic and early Mesozoic eras.</span>
Set this up as
10 = 40 (1/2)t/28
and solve for t in years.
10/40 = (1/2)t/28
log(0.25) = (t/28) log(0.5)
t = 28 log(0.25) / log(0.5) years = 56 years
Test the answer:
56 years = 2(28 years) = 2 half-lives, so the remaining amount should be 1/2 of 1/2 of the initial amount, i.e. 1/4 of the initial amount, and 10 mg = 1/4 of 40 mg.
