Question

Underline the important words and phrases.

Answer 1

The energy stored in coal and petroleum originally came to the earth from the sun. The bulk of the present-day supplies was laid down some 200 to 600 million years ago, when tropical conditions were widespread. Lush, swampy forests produced huge trees; warm coastal seas swarmed with microscopic forms of life. When these organisms died, much of their tissue was recycled as it is today through scavenging and decay. But a significant amount of dead plant and animal material was covered with mud, which prevented complete decomposition.

With the passage of time, layer upon layer of the fine sediment was deposited over the once-living material; the sheer weight turned the sediments to rock. Sandwiched between the layers, both coal and petroleum were produced and preserved under pressure. Coal was formed mostly of giant fern-like plants that have only small counterparts today. Coal may still be forming here and there on earth, but conditions are not right for the production of significant quantities.