The Salt of the Earth - Ocean Worlds: The Story of Seas on Earth and Other Planets - page 67

looking further, is part of an even-longer process that governs the
saltiness of the oceans and determines the chemical environment of
all the organisms that live in them.
The Salt in the Sea
Seawater is salty. What, then, is the saltiness? If we take the water out
of a litre (or a kilo) of ordinary seawater, then what we have left is
some 35 grams—an ounce and a half—of solid matter.
Taking this solid stuff into its constituent particles (that is, its ions),
most of these—more than 85 per cent of this residue—are of chloride
and sodium, and when crystallized together these make up sodium
chloride, or common salt. Then there are just six others that make up
most of the rest: sulphate at a little under 8 per cent, and magnesium
at just under 4 per cent; there is also calcium and potassium at a little
over 1 per cent each, and bicarbonate at a little under half a per cent,
and bromide at a fifth of a per cent.
That's reached over 99 per cent. Everything else is crammed into
the remaining fraction of 1 per cent. There is a lot of that everything
else. There is silica and iron and lithium and boron and tin and tanta-
lum and cadmium and mercury and arsenic and . . . there are measur-
able amounts, indeed, of nearly every element in the periodic table.
Water, as we have said, is a marvellous solvent.
How much, though, of the real rarities? One might consider gold
for instance—that most perennially fashionable of elements. There
are, appropriately enough, some fine cautionary tales to be told of
gold in seawater. One might start with Svante Arrhenius, a genius at
chemistry—and indeed a recognized genius, winning a Nobel Prize
in 1903. We will meet Arrhenius again in Chapter 9, as he explores
other worlds. On Earth, though, he considered (among many other
questions) the amount of gold in seawater. Around the beginning of
the twentieth century, he carried out analyses that gave a figure of