When was the % of CO2 in Earth's atmosphere at its lowest?

See title. With the rise to 455 ppm of CO2 (and likely higher for a while), I wonder what the lowest Earth's had, was.

If I'm not mistaken, the highest was during the Permian-Triassic mass extinction, in where the Siberian Traps may have been responsible for making burrowing -- and hence adaptations for stale air -- necessary?