[littlestymaar]

In addition to what others have said about the fact this planet doesn't have 8g at its surface, at 8g you could still have many lifeforms that exists on earth, but only the small ones. Gravity grows roughly as the cube of your size (because your volume does), but bones resistance only get n² (because it's the surface that counts), so the bone resistance / weight ratio is inversely proportional to your size.