地质专业英语教材.docx

1、地质专业英语教材1.The Earth The Earth is a nearly spherical planet. It has a circumference of approximately 25,000 miles (40,000 km), a polar diameter of about 7900 miles (12,714 km), and an equatorial diameter of 7927 miles (12,756 km). The three main units of the Earths interior are core, mantle, and crus

2、t. The diameter of the core is about 4300 miles (6900 km), and iron is probably its chief ingredient. The core consists of an inner part that seems solid and an outer part that appears fluid. The mantle is nearly 1800 miles (2900 km) thick and makes up about 84% of the volume of the Earth. Since the

3、 volume of the core is about 16%, the crust actually makes up a very small part of the Earth as a whole. The mantle and crust are solid except for relatively small masses of magma that develop occasionally within a few tens of miles of the surface. On the average, the crust is about six times as thi

4、ck beneath the continents as beneath the ocean floors- approximately 20 to 25 miles (32 to 40 km) vs. 3 to 4 miles (5 to 6.5 km). However, the continental crust is much thicker than average beneath the great mountain belts. As the term has been used recently, the lithosphere is the solid outer shell

5、 of the Earth, about 35 to 60 miles (50 to 100 km) or more in thickness. The rock most abundant in the upper part of the crust beneath the continents appears to be similar to granite in chemical composition and specific gravity (2.7). A heavier rock, probably similar to basalt in chemical compositio

6、n and specific gravity (3.0), is thought to underlie the floors of the oceans and also the granitic rocks of the continents. Thus the two-part continental crust differs fundamentally from the one-part oceanic crust; in fact, the difference accounts for the existence of continents and ocean basins.Th

7、e upper surface of the crust may be covered by water, by unconsolidated sediments, by soil and vegetation, or it may be exposed at the surface.2. The Outer Part of the Earths CrustBedrock is the solid rock that is exposed at the surface or immediately underlies soil and loose surface debris. Regolit

8、h is the relatively thin covering of soil and unconsolidated rock waste that hides the bedrock in most areas. Bedrock is continuous and may consist of any kind of rock, whereas regolith is discontinuous, although generally present. Regolith tends to be a few tens of feet thick or less, but may be mu

9、ch thicker, It may develop in place by the decay and disintegration of bedrock or consist of transported materials. Soil refers to the upper portion of the regolith which has been so altered by physical chemical, and biological processes that it can support rooted vegetation. However, soil may be ab

10、sent from an area.By direct observation, man has access to only a very thin outer part of the crust, the deepest mines penetrate less than 2 miles (3 km) beneath the surface, and the deepest wells about 5 miles (8 km). However, certain rocks now exposed at the surface may once have been buried sever

11、al miles below it.Chemical analyses have been for rocks of various types, and the proportions of the elements in the outer 10-mile (16 km) zone of the lithosphere have been estimated. Eight elements apparently constitute more than 98% by weight of this zone: oxygen (most abundant), silicon, aluminiu

12、m, iron, calcium, sodium, potassium, and magnesium (least abundant). The following mnemonic expression arranges these eight elements in the order of their relative abundances: “Only Silly Artists In College Study Past Midnight”. If the materials in the atmosphere and hydrosphere are added to those o

13、f the 10-mile zone, percentages are changed only slightly.Of these eight elements oxygen and silicon combined as silica (SiO2) make up about three-fourths of the total. Thus the silicate minerals are the most abundant in the crust, especially the feldspars, pyroxenes, amphiboles, micas and quartz.3.

14、 The Work of Running WaterFrom the atmosphere, water molecules fall upon the Earths surface as rain, snow, hail, and sleet. Some water evaporates or is taken up by plants, some runs off immediately into streams, and the remainder sinks into the ground. Much ground water later emerges at the surface

15、at a lower altitude and becomes runoff. Streams carry excess water from the land to the sea. In doing so, they erode valleys and help shape the Earths surface. They transport rock debris and dissolved materials, and eventually they deposit most of their sediment in the oceans. Stream activity, in co

16、mbination with weathering and masswasting predominates by far over other types of erosion such as wind, ice, or marine.Streams are important to man whether he uses them as sources of drinking water, irrigation, or electric power, or as places in which to fish, swim, or dump sewage. Valleys furnish t

17、he most convenient courses for many roads and railroads. The location of a number of important cities depended upon the navigability of large rivers. Civilization flourished first on fertile floodplains. Bridges, dams, and reservoirs have to be built. Frequent floods that cause loss of life and dest

18、ruction of property emphasize the importance of streams to man.4. Weathering and Soils The principal significance of the different climatic types to the student of geology lies in their influence on soil formation and on erosion. Each climatic environment places its own stamp upon the soils develope

19、d there, and each influences, through its control over vegetation, amount of rainfall, and evaporation losses, the geological processes involved in molding the details of the earths surface. Erosion, the process of removal of rock waste, will be discussed in later chapters; here, we will examine the

20、 influence of several different climatic environments upon the weathering of different rock types. The most familiar example of weathering is the etching and discoloration of the surface of an unpainted board left out-of-doors. Rock, exposed in the earths surface, also decays and leaches, but much m

21、ore slowly. If the product of rock decay is merely broken and discolored, it is called mantle rock; but if it is loose and porous enough for plants to find a foothold, it is called soil. Soil is more common than rock at the earths surface. Almost all outcrops of rock are less firm-more easily crumbl

22、ed and broken-than is the same rock at a depth of 20 or 100 feet. Many rocks that are black or steel gray where penetrated in mines, wells, or deep quarries are yellow or brown in outcrops. In some, the yellow color in a mere stain on or near cracks, but in others it is more pervasive and is accompa

23、nied by drastic changes in mineral composition of the rock. That the changes result from weathering is shown by observation on building stones. For example, the exposed faces of the sandstone used in the older buildings at Stamford University turned yellow in 5 to 10 years, and where exposed to repe

24、ated wettings, began to crumble in 20 to 30 years.5. Minerals Most minerals are chemical compounds; that is, they consist of two or more elements in combination. Of course there are exceptions, such as gold, copper, sulphur, and carbon, which may occur as elements by themselves as well as in chemica

25、l compounds. Minerals are naturally occurring substances. This statement rules out laboratory creations. Minerals have a reasonably definite chemical composition. Since they are naturally occurring substances, and net laboratory products, only rarely are they chemically pure compounds. For this reas

26、on, such properties as color may vary over a range as wide as from black to white, depending on the percentage of elements present for any mineral. Minerals also have certain physical properties, determined by their chemical composition and by the geometric arrangement of the atoms composing them. I

27、t is this atomic arrangement that determines the crystal form of a mineral. Other properties include such things as color, hardness, and specific gravity.In summary, then, a mineral may be defined as (1) a naturally occurring substance with (2) a fairly definite chemical composition and (3) characte

28、ristic physical properties by which it may be identified. In short, a typical mineral is a crystalline solid and is an inorganic substance. Most are chemical compounds, but a few, such as the diamond, may consist of a single element.Before we discuss the characteristics of individual minerals we sho

29、uld learn of the essential properties which are the chief means of their identification. Physical properties are the things we can see, or feel, or for such minerals as halite (rock salt), taste. True enough, the chemical composition is possibly the most diagnostic property a mineral possesses, but

30、few of us are going to pack along a fully equipped chemical laboratory to be used for mineral identification on a field trip. Since one of the critical differences between minerals and rocks is that minerals are approximately homogeneous substances, and most rocks are not, this means that one piece

31、of quartz will be about as hard as another piece, that it will have the same specific gravity, and if formed in a similar environment, it will have about the same crystal form.6. Common Minerals (1) On the basis of physical and chemical properties, some 2000 different minerals have been recognized a

32、nd described by mineralogists. However, this great number need not discourage us from attempting to understand the earths materials. Most of the 2000 minerals are rare and of interest mainly to specialists. Actually, fewer than two dozen are abundant, and a knowledge of only ten mineral types is an

33、adequate basis for a generalized understanding of the bulk of rocks which are most frequently encountered. Feldspar The most abundant mineral type, feldspar, composes over 60% of the rock materials in the earths crust. Strictly speaking, the term feldspar refers to a group of closely related minerals having generally sim