Comment by RegularOpossum

Oceans as an ecosystem are fascinating. This is simplified but on land the food chain is usually something like Plant-Herbivore-Predator but in the ocean the food chain is much longer, algae-Zooplankton--Predator-Predator-Predator-Predator-Predator-Predator-Predator. There's so much opportunities in the predator niche in the oceans that land animals keep going back to the ocean, because the evolutionary challenges were regularly worth it. This truly is a blue planet.