Specific Gravity of Solids:

Another significant characteristic of a solid is its density associative to that of pure liquid water at 4°C (around 39°F). Water is at its most dense at this temperature and is assigned a relative density of 1. The substances with relative density greater than 1 will sink in pure water at 4°C, and substances with relative density less than 1 will float in pure water at 4°C. The relative density of a solid, defined in this manner, is termed as the specific gravity. You frequently will see this abbreviated as sp gr. It is also termed as relative density.

You certainly can think of substances whose particular gravity numbers are greater than 1. Illustrations involve most rocks and virtually all metals. Though, pumice, a volcanic rock which is filled with air pockets, floats on water. Mainly all the planets, their moons, and asteroids and meteorites in our solar system have particular gravities greater than 1, with the exception of Saturn, that would float when a lake big sufficient could be found in which to test it!

Fascinatingly, water ice has particular gravity of less than 1; therefore it floats on liquid water. This property of ice is more important than you might at first assume. It permits fish to live underneath the frozen surfaces of lakes in the winter in the temperate and polar areas of the Earth since the layer of ice acts as an insulator against the cold atmosphere. When ice had specific gravity of larger than 1, it would sink to the bottoms of lakes during the winter months. This would leave the surfaces continuously exposed to temperatures beneath freezing, causing more and more of the water to freeze, awaiting shallow lakes would become ice from the surface all the way to the bottom. In such an atmosphere, all the fish would die during the winter since they wouldn't be able to extract the oxygen they require from the solid ice, nor would they be capable to swim around in order to feed themselves. It is hard to say how life on Earth would have developed if water ice had a specific gravity of greater than 1.