The ocean has always been highly acidic, and was only able to support complex life once enough coccolithophores bloomed and died, and the ocean dissolved enough

The ocean has always been highly acidic, and was only able to support complex life once enough coccolithophores bloomed and died, and the ocean dissolved enough of their carbonate sediments that it made the ocean less acidic. An increase in carbon dioxide has been slowly re-acidifying the ocean. If calcium carbonate-dense phytoplankton die off, the ocean gets fucked, and it'll no longer trap half the carbon dioxide generated on the planet, nor generate over half the planet's oxygen. https://en.wikipedia.org/wiki/Ocean_acidification https://en.wikipedia.org/wiki/Ocean_acidification