Although coal and petroleum are produced by degradation of bio- mass, yet we need to conserve them. Why?
Coal and petroleum were formed from the degradation of biomass. This biomass included ancient plant life which lived millions of years ago.
These resources are being utilized at a much faster rate than their formation. So they will be exhausted in the near future. And then we would need to look for alternative sources of energy.
This is the reason why we need to conserve them, although these resources are produced by the degradation of bio-mass.