Yesterday I said it seemed reasonable that Earth started 4.6 Billion years ago with an atmosphere 100 times the current pressure and almost all CO2. (About 10^18 tonnes). Where did it all go?
Photosynthesis only evolved about 3.5 billion years ago, so there were no plants waiting to grow like crazy. The answer was in the oceans.
When CO2 dissolves in water, it makes carbonic acid, H2CO3, the fizz in soda water. It is pleasantly acid when the CO2 pressure is 1.2 atmospheres and bubbles away in the wine glass or beer stein.
However, with a pressure of 100 atmospheres, it is 100 times as strong, and becomes a strong acid with a pH of 2.9, like very strong vinegar. It then dissolved many of the original silicate rocks, making sand and limestone. Initially the limestone was an inorganic sludge, but when life emerged it was converted to the limestone fossils we have today.
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