Translations of Encyclopedia about Geology

Solid Fuels

With the growing industrialisation, which started in the 18th century, the overall energy needs also grew. In addition to oil and natural gas, which are exploited on a larger scale since the 19th century, coal is a very important fuel today as it was in the past. More than 40 percent of energy used in western Europe is generated using coal.

Coal formed during millions of years, mainly during the Carboniferous, Jurassic, and Triassic periods. That means, that our coal reserves are between 350 and 250 million years old. At that time, the continents were covered by boggy forests. Large leaves and dead trees sank into the bog and were covered by water. Isolated from oxygen, the bacteria were unable to completely decompose the organic matter.

Dead vegetation gradually turned into a brown mass of organic material, in which large and small branches were still distinguishable. It was peat, which we find even today in bogs and moors. As additional layers of peat formed on top, the soft peat was compressed and the water was squeezed out. By pressure and weight, the peat layers were transported into the warmer regions of the earth's crust.

During chemical changes within the organic material, which were taking place in the earth's interior, the contents of carbon increased and the peat changed into lignite. This is a soft, brownish-black material, consisting of about 70 percent of carbon.

If lignite penetrates even lower, where the temperatures are still higher (for example, as a result of the tectonics), lignite changes into rocky black coal, or bituminous coal and, ultimately, into anthracite. The content of carbon in anthracite represents 90 percent and therefore anthracite has even higher heat value.

It is estimated that the earth contains approximately 6.5 billion tonnes of coal. Of this total, China, the former Soviet Union, and America combined own about 85 percent. It was calculated, that our coal reserves will last about 300 years.

A serious problem present when burning coal, is a high release of toxic waste. Many coal deposits have high contents of sulphur, which oxidises when the coal is burning, creating sulphur oxide. This gas escapes into the atmosphere and causes the well-known acid rain. The acid rain already poses an enormous problem in certain regions of the world. Coal-mining itself is often dangerous to health. As a result of continuously inhaling coal and rock dust, the miners suffer permanent damage to their lungs.

People valued oil already some one thousand years ago. In the 2nd century B.C., oil was used to heat luxurious baths. In Middle Ages, oil was considered as medicine for curing many different kinds of illness. Starting in the 19th century, oil increased in importance with the developing industrialisation as an important source of energy.

Oil and natural gas are products of the change of organic remnants of plants, ancient animals, algae, and bacteria.

In the Jurassic period (Mesozoic), large areas of Europe were under water. This water contained little oxygen and a number of tiny animals. These were settling on the ocean floor. For millions of years, the organic sediment in the ocean depths was affected by chemical reactions taking place at high temperatures of the earth's interior, changing from organic material into liquid and gaseous compounds containing oxygen and carbon (for example, producing bitumen).

(Editor's note: According to newer hypotheses of some scientist, part of oil, if not in its entirety, formed by the action of water on carbides of metals in the earth's mantle, analogously to the formation of acethylene in a carbide lamp.).

Hydrocarbons escaping into the neighbouring rock layers allowed the formation of the so-called oil mother lode (rocks containing oil). Due to low density, oil and natural gas rise to the highest accessible places.

Underneath some type of impermeable rock (for example, layers of shale), gas and crude oil collect in reservoirs floating on the underground water, where gas is nearer the surface and the oil underneath the gas. When the crude oil is extracted and refined, we obtain liquefied natural gas, gasoline, heating oil, and similar products.

The global distribution of the crude oil and natural gas deposits is very uneven. Extensive oil deposits are often found in the region of the continental shelves. However, not all shelf areas have been sufficiently explored. Oil companies are not sometimes ready to invest heavily in exploratory drilling. The largest estimated oil reserves are in the Middle East and Africa, followed by Central and South America.

Oil drilling may cause considerable pollution of the environment. During drilling, there are sometimes sudden eruptions, when thousands of barrels of oil spill out before the oil well can be closed. In addition, oil tanker accidents destroy marine habitat and cause death of millions of marine animals and birds, and ultimately people.

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