Trees and other plants take carbon from air, energy from the sub, and use it to build themselves. We take carbon from them and put it back into the air, using the excess energy to move and think.

Which was in the air in the past few months to handful of years depending on how fresh the food is and what it is (plant, animal). Unlike the CO2 from fossil fuels which was sequestered for millions of years. And had that not been harvested for food, it would have sat their being decomposed in a field somewhere returning that carbon right back into the atmosphere via animals and bacteria snacking on it as they broke it down.

The oil and coal only happen when organic matter is subjected to pressure and non-porous geological layers. Otherwise you get peat fields and those emit methane.