The half-life of protactinium-226 is 2 minutes if you started with 20 grams of pa-226 how much do you have after 8 minutes

Divide the amount in half for every 2 minutes

0 minutes = 20 grams

2 minutes = 20/2 = 10

4 minutes = 10/2 = 5

6 minutes = 5/2 = 2.5

8  minutes = 2.5/2 = 1.25 grams

the law of original horizontality explains:   why rocks appear in layers. correct answer: b the law suggests that all rock layers are originally laid down (deposited) horizontally and can later be deformed.   the principle is used by geologists to make assumptions about the relative ages of sedimentary rocks.