If a radioactive isotope had a half life of 1 billion years how much of it would be left after 1 billion , 2 billion, 3 billion, and 4 billion years

If the half-life is 1 billion years, then here's how much of the original sample remains after several periods of time:

1 billion years . . . . . 70.7%
2 billion years . . . . . 50%
3 billion years . . . . . 35.4%
4 billion years . . . . . 25%
5 billion years . . . . . 17.7%
6 billion years . . . . . 12.5%
7 billion years . . . . . 8.8%
8 billion years . . . . . 6.25%
9 billion years . . . . . 4.4%
10 billion years . . . . . 3.125%
11 billion years . . . . . 2.2%
12 billion years . . . . . 1.5625%
13 billion years . . . . . 1.1%

Volcanoes make new rocks so not ahotspots are the the stuff that makes volcanoes mid atlantic ridge(mar cause i’m lazy) is a constructive plate boundary so it makes sense that new rocks would be found near it, also the mar is in the middle of the ocean so it fits the description deep ocean trench, umm, there’s no ocean trenches to where you’re goingso the mar is most likely the answeri wouldn’t trust me but hey why not