To be restricted to - ограничиваться; заключать

To increase in - увеличиваться

To be accompanied by - встречаться вместе

To be altered by - изменяться под воздействием ч.-л.

To resist to - сопротивляться чему-то

Read the text «What is a fossil» and fulfill the after reading exercises.

WHAT IS A FOSSIL?

1. In common usage the word fossilcarries a distinctly derogatory implication but, as has been seen already, it referred originally to anything dug out of the ground. The root Latin word is fossilis meaning dug up, and therefore minerals as well as the remains of animals and plants were called fossils, but the term soon became to be restricted to the remains of animals and plants found in rocks. These used to be called petrifactions. It has been already noted that William Smith recognized that certain fossils were characteristic of the strata in which they occur, and indicated a definite age; these are known as characteristic fossils.

2. It is necessary now to consider how the remains of living things came to be preserved for such a long time. Immediately after death, organisms begin to decay. The slow process of oxidation takes place in the presence of oxygen, and simple compounds with hydrogen, carbon, nitrogen, sulphur and phosphorous are the final products. In the absence of oxygen, fermentation takes place, resulting in the formation of carbon and nitrogen. The channels through which gas has escaped from decaying organisms are sometimes preserved in sediments. In addition, bacteria and other organisms that live on dead material can cause decomposition.

3. The hard parts of organisms resist decomposition more effectively than the soft parts and become buried in and protected by sediment. Under favorable conditions either the complete animal or parts of it, may be preserved in their original state. Permeation by salt or complete impregnation of the tissues by oil or wax has a similar effect.

4. If organic remains are transported for any distance, they are usually broken or eroded so as to become almost unrecognizable, but in favorable circumstances, large numbers of dead animals can be deposited and entombed in sediments. In many instances the fossils are effectively part of the sediment in which they are embedded. The covering of the fossils by successive layers of sediment and the resulting increase in pressure causes the sediments to become compacted and lithified and also affects the fossils themselves.

5. The most important change is a reduction with increasing pressure, in the size of the pore spaces of the rocks and the consequent loss of water. This is accompanied by a series of chemical reactions, which are known as diagenesis. Such reactions frequently involve the remains of animals and plants. The processes of fossilization take place over long periods of time.

6. Clearly fossils are preserved under the most favorable circumstances; for all practical purposes they are restricted to the sedimentary environment and do not occur in igneous rocks which are produced by the crystallization of magma. Sedimentary rocks are formed mainly in seawater or lakes and most fossils are of organisms that lived in water. Terrestrial animals decompose quickly after death and are rarely preserved as fossils. Most fossils are the hard parts of organisms, which have been embedded in sediments and altered by chemical reaction. They may become calcified or silicified and thereby resistant to attack. Carbonization plays a special role in the preservation of plant fossils, the cellulose being reduced to carbon in the absence of air. Coal was formed in this way.

7.Fossils are not merely interesting or beautiful structures which occur in the sediments in which they live or in which they were buried, but are rather the means whereby the process of evolution can be traced and the clues to the interpretation of past events are recorded cryptically in sedimentary rocks to form a diary of Earth history.

(Robert Lauterbach “The World of Geology -The Earth then and now” 1983 Leipzig)

Fig. 2. Leaf imprint Fig. 3. Fossil fish

EXERCISES

2.1 Mark the stressed syllable on the following words from the text:

nitrogen, carbonization, characteristic, oxidation, bacteria, organism, impregnation, phosphorus, favorable, unrecognizable.

2.2 Find the words to the following definitions in the text and translate them into Russian.