[doc30]

It is also interesting that there is greater diversity of life in salt water environments than in fresh water. A part of this was the evolution of calcium based bones. Marine animals without bones depended upon the free calcium in ocean water. With the evolution of bones, fish could move into fresh water and survive because their bones would act as a calcium reservoir.

[Doctor Stochastic]

This article is in disagreement with the Creationist claim that the oceans are always getting saltier. Of course, the minerals could have been deposited in a Great Saltation Event.

[djf]

Another indicator is the fact that the chemical fuel of the neurons is the sodium/potassium gradient.

While there is certainly sodium and calcium in freshwater, I don't think there's anywhere near enough potash to support a freshwater evolution theory.

[furball4paws]

There's also one hell of a lot more salt water.