Abundance of Water

The abundance of water as the solvent of life is essential for life on the Earth. Ward and Brownlee in their discussion of the habitability of the Earth quote the abundance of water on the Earth as 0.1% and that of carbon as 0.05%. Later they quote the water abundance by weight as about half a percent, so this may give the range of uncertainty in the estimates. They contrast this with the concentrations in carbonaceous meteorites which contain up to 20% water and 4% carbon. Even though the water abundance seems low, it is actually quite large compared to the other rocky planets and the source of all the water on the Earth is still somewhat uncertain. The high abundance of water in the meterorites and in comets leads to the hypothesis that the water came from intense early bombardment of the Earth by such bodies. By contrast, the studies of moon minerals from the Apollo program revealed the minerals of the moon to be remarkably dry, with little or none of the hydration that is common in similar Earth minerals (Ward & Brownlee, Ch 11).

水作为生命的溶剂的丰富性对于地球上的生命是必不可少的。Ward和Brownlee在讨论地球的适宜性时引用了地球上的水含量为0.1%，碳的含量为0.05%。后来他们引用了按重量计算的水含量约为半个百分点，因此这可能给出了估计值的不确定性范围。他们将这一情况与碳质陨石中的浓度对比，后者含有高达20%的水和4%的碳。尽管水的含量似乎较低，但与其它类地行星相比，实际上相当高，而地球上所有水的来源仍 somewhat 不确定。陨石和彗星中水的高含量导致了水来自早期强烈撞击地球的假设。相比之下，阿波罗计划对月球矿物的研究显示，月球矿物非常干燥，其含水量极低，与类似地球矿物中的含水量相比几乎为零（Ward & Brownlee，第11章）。