Writing Skills: Summarising — NCERT Solutions

The present-day supplies of coal and petroleum were laid down about 200 to 600 million years ago when tropical conditions were widespread. At that time there were lush, swampy forests with huge trees, and warm coastal seas full of microscopic life.

With time, layer upon layer of fine sediment was deposited over the dead material. The sheer weight of these layers turned the sediments into rock. The coal and petroleum were then produced and preserved under pressure, sandwiched between the layers. In other words, the organic matter got compressed between rocks over time.