Your question needs to be written again: at the moment it is not clear what you mean. If you have been able to dedicate you life to science.... is talking about the past and present. And is REAL past and present. If you have done it, please tell us about it. "What field of science would it be? Is talking about a hypothetical situation, present and future. If you could choose a subject to study, what would it be? Perhaps you mean, "If you COULD dedicate your life to science, what field would you choose?

Hello! Hydrogeology. I love is water :)

Typo! Typing too fast! If you have been able to dedicate YOUR life to science.... (Line 2. Apologies)