How important are coal, oil and natural gas to the living and non-living things?

i need this urgent. It's an assignment on due. thanks guys!How important are coal, oil and natural gas to the living and non-living things?
During stone ages, less people live, and less important the coal %26amp; oil, The more people expand the more they are useful. Due to population growth at present century coincides with the building of cities and industries,without oil will result disorder, war.and death to mankind and living things.