溶解度。事实上,这个问题相当化学。溶解度是有点反直觉的:如果两个离子不溶性的解决方案,他们发现彼此并形成固体。你可以混合例如碳酸钠(溶)和氯化钙(溶)和碳酸钙(不溶性)。这就是为什么海洋不含钙——它们包含大量的碳酸盐。如果一个使海洋酸化,碳酸盐离子会少得多,我们可能确实有钙溶液中。我们不能有很多铁,铁离子是无法解决的,因为他们与氢氧根离子沉淀,你需要一个相当酸溶液以几乎没有可溶性铁。同样的现象解释了风化-雨水和aquifiers洗去离子根据自己的初始离子含量(包括酸性)。有什么重要的生理盐水?其离子很溶于几乎任何其他离子的存在。 This is why they are easy to leach from the stones and rocks and in fact we are almost done with this. This is why rivers don't bring much salt into the oceans these days - there is no much of them left. P.s. in regard to iron - long ago, before the first bacteria learned to produce oxygen, the ocean was full of iron. It was Fe2+ - this is the form stable when no oxygen is present. Fe2+ is much more soluble than the more oxidized form (Fe3+). This is how some large iron ore deposits formed.