Why Ice Floats

Almost every substance is denser as a solid than as a liquid. Water is the famous exception. Ice is about 9% less dense than liquid water, which is why it floats — and that quirk is vital for life. If ice sank:

1. Lakes and oceans would freeze from the bottom up
2. Fish and aquatic life would be crushed or frozen
3. Deep ice would never reach sunlight to melt
4. Earth might have become a permanent snowball.