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The exact composition of the deep-earth gases is not known because:

• it varies from place
• gases are not accessible for direct observation
• there are difficulties in interpretation
• the gas is contaminated while rising to the surface
• the underlying mantle is heterogeneous

Ex.14.

Подготовьте устное сообщение на тему “Теории происхождения нефти и газа”, продолжив и расширив следующую информацию:

The origin of oil and gas is one of the most important and difficult problems of petroleum geology.

It is a particularly difficult one because it has not yet been possible to determine the exact source bed from which anyparticular petroleum originated. Itwas recognized many years ago that any complete solution of the problem would require the active cooperation of several groups of scientists.

Geologists have been concernedprimarily in a study of the environment, conditions of sedimentation, and the organic content of petroleum source beds.

Biologists have made studies of the action of bacteria on organic compounds and organic materials.

Chemists have isolatedsome of the optically active constituents of both plants and crude oils, and have showncertain chemical and physical similarities between them.

As further research work and investigations on this problem arecompleted enoughdata may be assembled to enable scientists to solve the problem of the origin of petroleum.

Many theories on the origin of petroleum have beenproposed. They may be divided into two groups: the organic and the inorganic.

Unit IV. Text translation.

Text I