Natural gas deposits can be up to 500 million years old. Coal deposits were formed about 300 million years ago. Oil deposits 65-250 million years old. About 65 million years ago the Chixculub meteor struck earth, and wiped out 75% of life on earth. (A useless tidbit is that was a fast mass extinction taking place over 1-2 million years.) Life as we know it developed in a short period time with all that carbon trapped deep under the earth. I don’t know why anyone would think putting that back in the atmosphere is anything but a bad idea, because we are delving deep into the unknown.
I don’t buy into global warming thing, I do worry about the carbon.