Do we even know what we're looking for? Maybe some expected geologic features are the fossils of the first life? How do we know if the tell-tale signs produced

Do we even know what we're looking for? Maybe some expected geologic features are the fossils of the first life? How do we know if the tell-tale signs produced by modern simple life couldn't be also produced by proto-life? Maybe they used some of the same processes without all the other stuff modern life does? Maybe life was bound to one location before it invented cells, and we just never checked that location? Maybe that location is now thousands meters below some ocean?