Complex sentence: This argument could have been made every time a new biological life form was found, and would have been correct every time; this does not mean it is impossible that in the future a biological life form that does not require water could be discovered.
Split into simpler sentences: This argument could have been made every time a new biological life form was found, and would have been correct every time. While it is possible that in the future a biological life form that does not require water could be discovered.