You posted this question in the wrong forum, so I moved it to the correct forum.

This is one reason why you want to use RMAN to backup your database. You can do block level recovery with RMAN. You should probably get an RMAN backup now before you try to recover any blocks, if you don't already have an RMAN backup.

Here is a document on getting started with RMAN
http://docs.oracle.com/cd/B28359_01/...0/rcmquick.htm

Here is a document for doing block level recovery.
http://docs.oracle.com/cd/B28359_01/...0/rcmblock.htm

Block level corruption should not happen as a matter of course, however it is relatively easy to deal with, once you have a good backup and recovery strategy.