What rare materials are needed for life on earth ?
Additionally , in the nondirectional meandering from initial life to humans , other low - probability happenings may have been the transition from prokaryotic cells to eukaryotic cells ( with separate nucleus , organelles , specialization , and a cytoskeleton allowing the cell to take on different shapes ) and the transition from single - cellular life to multicellular life , which was recorded in the Cambrian Explosion of 530 million years ago when significant numbers of organisms evolved hard body parts , although multicellular life perhaps first started to evolve a couple of hundred million years before that .