I've often thought there were too many assumptions being made about any life being similar to life on Earth. It would be quite ironic if our own planet harbored types of life dissimilar to "normal" life.
I've never read a truly compelling explanation why all life must be carbon and water based. Just because that is what we are and what we have seen does not necessarily mean there are no other ways to "design" life. I would think life may have evolved into a quite different form under quite different circumstances.
