1 is incorrect because, although t.he speaker mentions this aspect, he does not say it influenced him in his choice of career. 2 is incorrect for the same reason. 4 is incorrect for the same reason.
3 is correct because the speaker says: I suppose the reason I got into geology was, well, as a kid I was fascinated by fossils – the fact that they went back countless years, long before there were any people on the planet. That was exciting and, um, they were beautiful loo. And one thing led to another.