How did carbon enter the ecosystem? So there's a bunch of CO2 in the atmosphere, there's oodles of coal and oil under ground, and there's a lot of trees built by carbon.

But all that is just a cycle CO2 -&gt; wood -&gt; coal/ top soil nutrients. Also fauna will eat plant matter.

But how did it all start? Was there some single celled organism munching on graphite or something?