The thing is, sometimes you won't know whether you like something or not before you try it. But sometimes you can have a feel by reading the journal/magazines/books, and looking into the life of somebody who has succeeded in the area you're looking into.
Since you've chosen the general areas of life sciences and chemical, check out the dudes and gals who have made it big in life sciences and chemical. Can you see yourself being them in 10 years? Do you want to be them?
That's about the best you can do for now. Sometimes, as you get older, your interest can change. But you don't know when or what it'll be sometimes. So that's fine. It's better to pick one and decide to dedicate yourself rather than to hesitate and finally pick one that you're just "OK" with.