Question

Combine related points.

Answer 1

1) Energy stored in coal, petroleum came from sun
2) bulk of present-day supplies laid down some 200-600 million years ago
3) abundance of microscopic forms of life in tropical conditions
4) organisms died – tissues recycled through scavenging and decay
5) prevention from total decomposition- considerable portion of dead animal and plant remained covered with mud
6) over the years, sediments hardened to form rocks
7) production of coal, petroleum under pressure
8) present day conditions not suitable for coal-formation