if ice did not float, the world would be a hot mess. Ice reflects lots of sunlight, so if it was at the bottom, our world would be significantly hotter. Additionally, plants grow at the bottom, so if they were trapped in ice, the water would run out of oxygen and everything would die. Bottom feeders would not exist, because they would be frozen. Also, the ice would just like on, because the water above prevents it from melting entirely, leading to all of our bodies of water eventually freezing.
