Answer:
If solid ice were denser than water, it would sink. In the most extreme conditions, there would be no way to melt the ice in deep lakes and oceans, which would thicken from the bottom to the surface, forming permanently frozen bodies of ice and disrupting Earth's water cycle.
Step-by-step explanation:
This ice layer insulates the water below it, allowing it to stay liquid, which allows the life within it to survive. If ice sank, the liquid water on top would also freeze and sink, until all the liquid water became frozen. Water is less dense as a solid, than as a liquid, which is why ice floats.