I can't recall the exact numbers. CO2 has been sequestered in limestone over time which dropped the CO2 levels. Limestone is from the shells of marine life that falls to the bottom of the oceans and lakes.
In a few million years the CO2 level would have dropped to a level which would have extinguished all plant life on earth. So earth created humans to burn fossil fuels to save life on earth.
also
150 - 200 ppm threatens plant growth, although slow and drought-vulnerable growth is possible under optimal conditions of rain and soil and sunlight near the equator. Below 150 - 100, few can grow at all even under the best of conditions.
Now, with CO2 raised from 280 ppm to 415 ppm, EVERY PLANT on earth is growing 12% to 27% faster, taller, greener, more productively and more drought-tolerant. Trees are actually growing so fast now that the standards boards have had to slightly reduce the nominal rated strength of 2x4’s and cut lumber to reflect the less dense grain structure.
