The density of ice is lower than the density of water. As a result, ice forms only on the surface of the water bodies (i.e., lakes), allowing water animals and plants not to be frozen and to survive in cold water. If ice sank, water bodies in lakes and oceans would become frozen. As a result, all organisms that live in the oceans and other water bodies would die and could not survive during cold seasons. As a result, the amount of phytoplankton would significantly decrease, leading to the reduced production of oxygen. In this case, live on the Earth would become impossible.