Questions to discuss.• What is the process of the formation of a lava lake? • How can the lens form of lave lakes be accounted for? • Compare water and lava lakes. Text 10 THE DEEP-EARTH-GAS HYPOTHESIS I There is much evidence indicating that earthquakes release gases from deep in the earth's mantle. Such gases may indicate methane of nonbiological origin, which could be a vast resource of fuel. It is widely believed that the earth's supply of hydrocarbon fuels will be largely used up in the foreseeable future, the most desirable ones (oil and natural gas) within a few decades and coal within a few centuries. Diverse evidence leads us to believe that enormous amounts of natural gas lie deep in the earth and that if they can be tapped, there would be source of hydrocarbon fuel that could last for thousands of years. The hypothesis that there is much gas deep in the earth also provides a unified basis for explaining a number of otherwise rather puzzling phenomena that either give warning of earthquakes or accompany them. The exact composition of the gas is not known, since the observational evidence is scattered and not easily interpreted. Volcanic eruptions bring gas out from the interior of the earth. It is not possible, however, to deduce from such observations the initial composition of the gas while it was still deep in the earth. Gases released during earthquakes are probably more reliable samples of what resides in the deep crust and the upper mantle. The sampling of such gases is just beginning, and the data will not yet support confident conclusions. One can assume that the composition of the deep-earth gases varies from place to place, since the location of mineral deposits in the crust suggests that the underlying mantle is quite
The notion of non-biological methane runs counter to the prevailing view in petroleum geology that virtually all the oil and natural gas in the earth is of biological origin. In that view the carbon in hydrocarbon fuels was originally derived from atmospheric carbon dioxide, and the energy to dissociate the carbon and the oxygen came from sunlight in the course of photosynthesis by green plants. The bural of some of these organic compounds before they could become oxidized would then have provided the source materials for oil and gas. It cannot be doubted that this process contributed to the genesis of much of the petroleum that has been recovered, but there may be more to the story. П 1 The hypothesis that the earth contains much non-biological hydrocarbon begins with the observation that hydrocarbons are the dominant carbon containing molecules in the solar system. The universe is made mostly of hydrogen, and the evidence of cosmochemistry suggests that the earth and the rest of the solar system originally condensed out of a hydrogen-saturated nebula. Most of the carbon in meteorites, which provide the best clues to the origin, composition of the inner planets, is in the form of complex hydrocarbons with some chemical similarity to oil tars. The picture we favour is of dual origin, with some hydrocarbons derived from buried organic sediments and probably much larger amount added to those hydrocarbons by augmentation from a stream of non-biological methane. Let us now examine some of the evidence for the escape of methane from the interior of the earth. A likely place to look is along the crustal faults and fissures of the tectonic-plate boundaries, which ought to provide the best access to the deep interior. Indeed, hydrocarbons appear to be clearly associated with such plates. Another line of evidence connecting non-biological hydrocarbons with such features is the striking correlation between the major oil and gas regions and the principal zones of past and present seismic activity. Oil fields often lie along actiye or ancient lines. Most of the known natural seeps of oil and gas are found in seismically active regions. The association suggests to us that the deep faults may provide a conduit for the continuous input of nonbiological methane and other gases streaming up from below. Moreover, the upward migration of methane and other gases in fault zones may contribute to the triggering of earthqnakes. Seismologists have long recognized a difficulty in accounting for deep earthquakes. Yet earthquakes have been recorded from depth of as much as 700 kilometers and if the fracture is strong enough to fracture the ground up to the surface, the gas escaping may generate some of the peculiar phenomena that have been reported to accompany many major earthquakes. The phenomena include flames that shoot from the ground, "earthquake lights", fiece bubbling in bodies of water, sulphureous air and visible waves rolling slowly along alluvial ground. Tsunamis (large, earthquake-caused waves at the sea that are often highly destructive) may be an analogous phenomenon. It is usually assumed that they are generated by a sudden displacement of an enormous area of the sea floor over a vertical distance comparable to the height of the wave.
Many of the precursory phenomena are detected only by instruments. Included in this category are changes in the velocity of seismic waves through the ground, in the electrical conductivity of the ground, in the tilt and elevation of the surface, in the chemical composition of gases in the soil and the ground water. The time between the onset of a precursor and the earthquake ranges from minutes to years. Not all precursors of earthquakes can be detected only by instruments. Some are so obvious to the senses that they have been recognized since ancient times. We believe these effects too are caused by an increased flow of gas through the ground. Among these "microscopic" precursors are dull explosive noises of unknown origin, the strange behaviour of animals, local increases of temperature, bubbling of water in wells and flames from the ground. Many other lines of investigation can elucidate the degassing processes of the earth. Variations of the methane content of the atmosphere may be observable. Changes of fluid pressure in the ground can be monitored. No one has any firm evidence on the diverse gas regimes more than a few kilometers below the surface or on the quantity or frequency of the various gases emerge. Our present attempt to formulate a relatively simple hypothesis to account for numerous previously unrelated facts will doubtless turn out to be in places oversimplified or overstated. We hope, however, that it will stimulate further research in this fundamental field of geophysics and geochemistry, leading perhaps to the discovery of large new sources of fuel and in any case to an improvement in the understanding of the earth and its resources. \ I Ш Give the Russian for: a vast resource of fuel; within a few decades; there is much evidence; to be used up; to provide a unified basis for..; to deduce from the observations; confident conclusions; to run counter to...; it cannot be doubted that... ■ Give the English for: >;полагают, что...; обозримое будущее; разнообразные доказательства; предупреждать о...; первоначальный состав; надежные образцы; по ряду причин; преобладающая точка зрения; по ходу фотосинтеза Ш Focus on structures. • The exact composition of the gas is not known, since the evidence is scattered. • The earth's supply of hydrogen fuel is believed to be largely used up. • The hypothesis... provides a unified basis for explaining a number of otherwise puzzling phenomena. ^w J> Questions to discuss. • Why is the problem of hydrocarbon fuel supply considered to be urgent? • Is it possible to deduce the exact composition of the gas released
Ш Give the Russian for: Diverse evidence leads us to believe that.... It is widely believed that... One can assume that... For a variety of reasons... It cannot be doubted that... In that view... To account for previously unrelated facts... In any case... Another line of evidence... Many other lines of investigation... Ш Give the English for: Широко известно, что... Разнообразные факты заставляют нас поверить в то, что... Гипотеза дает универсальную основу для понимания природы явлений иначе трудно объяснимых. Данные наблюдений отрывочны и их объяснение затруднено. Из подобных наблюдений невозможно сделать вывод о... По ряду причин данные пока не дают достаточных оснований для того, чтобы... Не пытаться приуменьшить важность других исследований... Противоречить общепринятым взглядам... Не может вызывать сомнения тот факт, что... Данные дают основания полагать, что... Другая линия доказательств заключается в том, что... Попытка предложить относительно простое объяснение сложным, не связанным между собой фактам, может привести к несколько упрощенному пониманию... Ш Explain and expand. The exact composition of the deep-earth gases is not known because: — it varies from place to 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. ■ Challenge Translation I "THE CEMETERIES OF STONY FORESTS"; Entire trunks of fossilized trees — indeed, whole cemeteries of stony forests — emerge from the bluffs and fall in pieces to the beach below PARTI Recently, I had a reading experience I can only describe as meta-morphic. For years now I've been writing a book of my own... In an attempt to actually, finally complete it, I escaped New York City for several weeks and hid out in Cape Breton, at the far northern end of
I stopped at Joggins on my drive up to Cape Breton. After several hours wandering on the beach, I'd gathered several pounds of seemingly matchless fossils: signatures of ancient grasses, the talon imprint of some dinosaur, intriguing whorls of indeterminate origin. I lugged them to the interpretative center, a small brown house on the town's single street. The center had a collection, too, gathered over years by local experts. Tiny claw prints of lizards. Articulated silhouettes of insect wings. Whole root systems of trees. In comparison, in an instant, my collection seemed pathetic, even, I began to suspect, illegitimate. The center's guide, a high-school senior and the grand-daughter of the curator, offered to identify what I'd found. My fossils merely looked like fossils. "They're just rocks," she said gently. Things improved a few days latter. The house I'd rented was set back from a low bluff overlooking the sea. In the face of the cliff I recognized the same sedimentary features I'd seen at Joggins: pancake layers of geological strata, dark traces of coal, a scree of fallen rocks on the shoreline below. At low tide I went down and poked around. The rocks were of sandstone, siltstone, and shale: thin layers of sediment, each layer representing varying degrees of solidity. With care, and the can opener on my jackknife, I found I could pry the layers apart. Inside were the fossils I'd sought: stems, leaves, roots, their textures finely etched on pages of stone. Slowly, I picked through the fallen debris, pulling apart, marveling. Shreds of rock fell in my trail. The pressed flora of an ancient Earth was revealed to me. When I looked around at the rubble still left to examine, suddenly I saw not rocks but books: mounds of blackened, soggy tomes; heaps of hardcovers, their titles indecipherable; leaves of text that crumbled at my touch. At one point I came across a rock as big as me. It stood on edge with its thin layers of sandstone aligned vertically, facing me like a giant prehistoric thesaurus. I peeled away the leftmost page — it took two hands — and felt the rush of ages.
|
heterogeneous. For a variety of reasons we think methane of nonbio-logical origin is one of the principle deep-earth gases, and it will be the focus of our discussion here, although we do not mean to minimize the possible importance of other deep-earth gases in the phenomena associated with earthquakes.
