Question

were the prokaryotes the first organisms on earth?

Answer 1

The oldest life fossils are very simple - prokaryotic no doubt and not that different from many of today's prokaryotic cell structure. Evolution in general seems to be an increase in complexity. Thus the first cells would logically be prokaryotic, or at least noneukaryotic. This is because prokaryotic cells are much simpler than prokaryotic cells which contain multiple membranous organelles to complicate their structure.