Well, its extremely hot in the hydrothermal vents. Scientists simply believed it would be impossible for anything to survive due to the heat. Bacteria and micro-organisms were able to adapt to growing there, though. So in short words, they survived extreme conditions teaching scientists that life was quite adaptable.
Weird fun fact: In Switzerland it is illegal to own just one guinea pig. Felt the need to mention that ^ Sorry, I know it has nothing to do with the question but i felt it was worth speaking of.
