Carbon dioxide concentrations dropped from 4,000 parts per million during the Cambrian period about 500 million years ago to as low as 180 parts per million during the Quaternary glaciation of the last two million years:
https://en.m.wikipedia.org/wiki/Carbon_dioxide_in_Earth%27s_...
I would argue 500 million years ago is not ”not so long ago”. The Cambrian period also didn’t have more than a microbial soil crust living outside of oceans.