Restoring Original Images in Aperture

I just installed Aperture and was playing around with some of the settings.... exposure, saturation, brightness, levels, highlights, shadows, etc, etc.... to make a long story short... the pictures I played around with look horrible! Now, when I open up Aperture it displays ALL pictures in my photo library in this messed up manner. Is there some "undo" button that will revert and/or display all the photos in their original/correct manner?