# Water Density / Expansion and Life

## Main Question or Discussion Point

What molecules or chemicals, other than water [H20] (that I know of), are less dense as they become cooler and their electrons slow? This is broad question, I know, but my question relates to the fact that much of our conditions of life rely on the density of water as it becomes a solid (see the last post at: [URL [Broken] by Jim Stringer). If there are other molecules or chemicals that react the same way then there could be other forms of life, besides Earth's terrestrial, outside of Earth so this is where my question originates from. I realize this may be a question of a green-horn, but I ask it nevertheless. I know there could be thousands, but I am interested in the simple molecules containing between 4 elements and 6 elements.

Thank you.

Last edited by a moderator:

Related Other Physics Topics News on Phys.org
Hi descender,
I know of no other material so important to life on earth but do you know that life would never have originated if the freezing point of water had been at - ~4 degrees C rather than + ~4 degrees? Clue: water would freeze from the bottom up! Cheers, Jim

chroot
Staff Emeritus
Gold Member
NEOclassic,

If water froze at -4 degrees C it would make no difference. What make lakes freeze "top-down" is that liquid water above its freezing point is more dense than ice. This quality has nothing at all to do with the actual freezing temperature.

- Warren

HallsofIvy
Homework Helper
Chroot, you missed the point. Water, as it is freezing, expands UNTIL it reach about -4 degrees Celcius after that it "shrinks" like everything else. NEOclassic's point is that if water froze at -4 degrees, then ice would not be lighter than water and water would freeze from the bottom up.