Although coal and petroleum are produced by degradation of bio-mass, yet we need to conserve them. Why?

Explanation

Coal and petroleum were formed from the degradation of bio-mass millions of years ago. As these resources are being utilised at a much faster rate than their formation, 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 degradation of bio-mass.