When our great deposits of fossil fuels were being laid down in the Carboniferous, efficient decomposers / recyclers of dead wood and plant material (chiefly hi

When our great deposits of fossil fuels were being laid down in the Carboniferous, efficient decomposers / recyclers of dead wood and plant material (chiefly higher basidiomycete fungi) had not yet evolved. Nowadays there is much less opportunity for dead organic material to accumulate in the kind of quantities that geological processes can turn into significant oil reserves.