Help with Macbook Air overheating

Just recently my macbook air has started to overheat an abnormal amount which tremendously effects the battery life. I assume this is because of the fan running throughout each computer use. I am a college student, so I primarily use the computer for research and other school related functions. Let me attempt to describe each use. First of all, the battery begins at 100% and after about five minutes I can faintly hear the fan. About 15 minutes into each use the fan is running at full blast and is easily audible. I can also easly feel the heat from the computer through the keyboard. Before the over heating and battery life became a problem I would be able to use the computer anywhere from seven to eight hours stright on a single charge. Now i can barely use the thing for two hours. The source of the heat seems to be comming from below the Tab, 1,2,3 section on the keyboard. I was not even aware that there was even a fan in the computer unit just recently when the overhearing became a problem. I also want to mention that all software is up to date.