石油地质研究生专业英语学习第1课地质学基础.docx

1、石油地质研究生专业英语学习第1课地质学基础Section AEARTH IN SPACE AND TIMEThe Early Solar SystemIn recent decades, scientists have been able to construct an ever-clearer picture of the origins of the solar system and, before that, of the universe itself. Most astronomers now accept some sort of Big Bang as the origin of

2、 todays universe. At that time, enormous quantities of matter were created and flung violently apart across an ever-larger volume of space. The time of the Big Bang can be estimated in several ways. Perhaps the most direct is the back-calculation of the universes expansion to its apparent beginning.

3、 Other methods depend on astrophysical models of creation of the elements or the rate of evolution of different types of stars. Most age estimates overlap in the range of 15 to 20 billion years, although a few researchers suggest an age closer to 10 billion years.Stars formed from the debris of the

4、Big Bang, as locally high concentrations of mass were collected together by gravity, and some became large and dense enough that energy-releasing atomic reactions were set off deep within them. Stars are not permanent objects. They are constantly losing energy and mass as they burn their nuclear fue

5、l. The mass of material that initially formed the star determines how rapidly the star burns; some stars burned out billions of years ago, while others are probably forming now from the original matter of the universe mixed with the debris of older stars.Our sun and its system of circling planets, i

6、ncluding the earth, are believed to have formed from a rotating cloud of gas and dust. Most of the mass of the cloud coalesced to form the sun, which became a star and began to shine, or release light energy, when its interior became so dense and hot from the crushing effects of its own gravity that

7、 nuclear reactions were triggered inside it. Meanwhile, dust condensed from the gases remaining in the flattened cloud disk rotating around the young sun. The dust clumped into planets, the formation of which was essentially complete over 41/2 billion years ago.The PlanetsThe compositions of the pla

8、nets formed depended largely on how near they were to the hot sun. The planets formed nearest to the sun contained mainly metallic iron and a few minerals with very high melting temperatures, with little water or gas. Somewhat farther out, where temperatures were lower, the developing planets incorp

9、orated much larger amounts of lower-temperature minerals, including some that contain water locked within their crystal structures. (This development later made it possible for the earth to have liquid water at its surface.) Still farther from the sun, temperatures were so low that nearly all of the

10、 materials in the original gas cloud condensedeven materials like methane and ammonia, which are gases at normal earth surface temperatures and pressures.The result was a series of planets with a variety of compositions, most quite different from that of earth. This is confirmed by observations and

11、measurements of the planets. For example, the planetary densities listed in table 1.1 are consistent with a higher metal and rock content in the four planets closest to the sun and a much larger proportion of ice and gas in the planets farther from the sun. These differences should be kept in mind w

12、hen it is proposed that other planets could be mined for needed minerals. Both the basic chemistry of these other bodies and the kinds of ore-forming or other resource-forming processes that might occur on them would differ considerably from those on earth, and may not lead to products we would find

13、 useful. (This is leaving aside any questions of the economics or technical practicability of such mining activities!) In addition, our principal current energy sources required living organisms to form, and so far, no such life-forms have been found on other planets or moons. Venusclose to Earth in

14、 space, similar in size and densityshows marked differences: Its dense, cloudy atmosphere is thick with carbon dioxide, producing planetary surface temperatures hot enough to melt lead through runaway greenhouse-effect heating. Mars would likewise be inhospitable, as will be seen later in the chapte

15、r.Earth, Then and NowThe earth has changed continuously since its formation, undergoing some particularly profound changes in its early history. The early earth was very different from what it is today, lacking the modern oceans and atmosphere and having a much different surface from its present one

16、, probably more closely resembling the barren, cratered surface of the moon. The planet was heated by the impact of the colliding dust particles and meteorites as they came together to form the earth, and by the energy release from decay of the small amounts of several naturally radioactive elements

17、 that the earth contains. These heat sources combined to raise the earths internal temperature enough that parts of it, perhaps eventually most of it, melted, although it was probably never molten all at once. Dense materials, like metallic iron, would have tended to sink toward the middle of the ea

18、rth. As cooling progressed, lighter, low-density minerals crystallized and floated out toward the surface. The eventual result was an earth differentiated into several major compositional zones: the central core; the surrounding mantle; and a thin crust at the surface. The process was complete befor

19、e 4 billion years ago.Although only the crust and a few bits of uppermost mantle that are carried up into the crust by volcanic activity can be sampled and analyzed directly, we nevertheless have a good deal of information on the composition of the earths interior. First, scientists can estimate fro

20、m analyses of stars the starting composition of the cloud from which the solar system formed. Geologists can also infer aspects of the earths bulk composition from analyses of certain meteorites believed to have formed at the same time as, and under conditions similar to the earth. Geophysical data

21、demonstrate that the earths interior is zoned and also provide information on the densities of the different layers within the earth, which further limits, their possible compositions. These and other kinds of data indicate that the earths core is made up mostly of iron, with some nickel and a few m

22、inor elements, and that the mantle consists mainly of iron, magnesium, silicon, and oxygen combined in varying proportions in several different minerals. The earths crust is much more varied in composition and very different chemically from the average composition of the earth. As is evident from th

23、at table, many of the metals we have come to prize as resources are relatively uncommon elements in the crust.The heating and subsequent differentiation of the early earth led to another important result: formation of the atmosphere and oceans. Many minerals that had contained water or gases in thei

24、r crystals released them during the heating and melting, and as the earths surface cooled, the water could condense to form the oceans. Without this abundant surface water, which in the solar system is unique to earth, most life as we know it could not exist. The oceans filled basins, while the cont

25、inents, buoyant because of their lower-density rocks and minerals, stood above the sea surface. At first, the continents were barren of life.The earths early atmosphere was quite different from the modern one, aside from the effects of modem pollution. The first atmosphere had little or no free oxyg

26、en in it. It probably consisted dominantly of nitrogen and carbon dioxide (which is the gas most commonly released from volcanoes, aside from water) with minor amounts of such gases as methane, ammonia, and various sulfur gases. Humans could not have survived in this early atmosphere. Oxygen-breathi

27、ng life of any kind could not exist before the single-celled blue-green algae appeared in large numbers to modify the atmosphere. Their remains are found in rocks as much as several billion years old. They manufacture food by photosynthesis, using sunlight for energy, consuming carbon dioxide, and r

28、eleasing oxygen as a by-product. In time, enough oxygen accumulated that the atmosphere could support oxygen-breathing organisms.Life on EarthThe rock record shows when different plant and animal groups appeared. Some are represented schematically in figure 1.4. The earliest creatures left very few

29、remains because they had no hard skeletons, teeth, shells, or other hard parts that could be preserved in rocks. The first multicelled oxygen-breathing creatures probably developed about 1 billion years ago, after oxygen in the atmosphere was well established. By about 600 million years ago, marine

30、animals with shells had become widespread.The development of organisms with hard partsshells, bones, teeth, and so ongreatly increased the number of preserved animal remains in the rock record; consequently, biological developments since that time are far better understood. Dry land was still barren

31、 of large plants or animals half a billion years ago. In rocks about 500 million years old is the first evidence of animals with backbonesthe fishand soon thereafter, early land plants developed, before 400 million years ago. Insects appeared approximately 300 million years ago. Later, reptiles and

32、amphibians moved onto the continents. The dinosaurs appeared about 200 million years ago and the first mammals at nearly the same time. Warm-blooded animals took to the air with the development of birds about 150 million years ago, and by 100 million years ago, both birds and mammals were well estab

33、lished.Such information has current applications. Certain energy sources have been formed from plant or animal remains (see chapter 13). Knowing the times at which particular groups of organisms appeared and flourished is helpful in assessing the probable amounts of these energy sources available and in concentrating the search for these f