Like I said. The phytoplankton of that time, is not the same phytoplancton we have today. There are evolutionary drivers that push lifeforms towards efficiency

Like I said. The phytoplankton of that time, is not the same phytoplancton we have today. There are evolutionary drivers that push lifeforms towards efficiency. A thick, protein rich, acid resistant shell is much more expensive, than a thin, calcium rich one. Well... until the day a new outlier species comes along and turns back the clock by 3 million years, in 100. To put that into perspective, it's like asking you on vacation to the bahamas giving 7 days to pack your stuff, and when the time to leave arrives I yell: "Surprise! We're actually going to siberia, time to pack your winter coat, the plane leaves in 20 SECONDS!"