From article
"Professor Falkowski calculates that in the past two billion years, about 15 billion billion tonnes of carbon has been removed from the atmosphere and locked into the Earth's crust."

Falkowski doesn't say this 15 billion billion tonnes of carbon remained in the earth's crust to the present day.

In the last 2 billion years, we have had subduction from earth's tectonic plate, and when this occurs CO2 is released back into the atmosphere. So there is a recycling of this CO2.

I mentioned Venus's CO2 atmospheric mass.
Is there any reason to assume that Earth has less carbon than Venus?
Venus is Earth's nearest planet. Venus is slightly smaller than Earth. And of course Venus doesn't have a Moon, nor does it have a fast rotation. Lacks a magnetosphere, has higher orbital speed [impactor hit it at faster velocity] and it should have less impactor hitting [as Mars has more impactor hitting it than compared to Earth].
It seems that if anything Earth should have more carbon than compared to Venus.
Anyways that's why I included Venus.

But the major way one is going to get that much carbon removed from the atmosphere would due to the recycling of the CO2, and I don't know if Falkowski calculated it right, nor if he meant CO2 when he said carbon.