Sharks don't particularly have a great interest in divers. It seemed that in a normal dive, I would jump in the water, and one or two gray reef sharks would swim in and kind of check me out - and then they would keep their distance. So they weren't particularly threatening or anything to be afraid of.
Life is fragile: it thrives only in a narrow range of temperatures between freezing and boiling. How lucky that our planet is just the right distance from the sun: a little farther, and the death of the perpetual Antarctic winter - or worse - would prevail; a little closer, and the surface would truly fry anything that touched it.