Oil and Gas
Petroleum and natural gas are the chemically altered remains of microscopic plants and animals that lived in considerable abundance in ancient seas. As these remains settled with sediment to the bottom of oxygen-poor seas and were buried beneath thick layers of sediment, hydrocarbons (hydrogen and carbon) were altered to waxy kerogen in black shales such as the Ohio Shale. As the rock became more deeply buried and warmer, oil began to form from the kerogen at about 90 degrees C and then to natural gas at about 160 degrees C. Temperatures above 250 degrees C destroyed the oil and gas. This temperature range is known as the Oil Window. Later, the oil and gas may flow from the source rock to a reservoir rock where it may be trapped between the sediment grains and discovered and produced by oil and gas companies.