It's an interesting point to cherry-pick, and it's fair to question the affect of atmospheric CO2 on aquatic life, but you can't say that CO2 levels are at historic lows when they're up 30% in the past 60 years [1].
I thought I made it very clear the historic period I was referring to. Questioning the relevance is indeed apropos. However, the semantics, I do not understand.
Regarding the last 60 years, I think it is very unlikely that the earth has not had a period where atmospheric CO2 concentrations have not rose as quickly. The volcanism, planetary impacts, and die offs of the past had to have had similar impacts. Yet, shelled creatures survived to the extant that they are ubiquitous in the earth's waters today.
There indubitably have been extinction events and perhaps some of them have been caused by ocean acidification.