Grammar focus Perfect Tenses

Task 1. Read the sentences. Name the grammar tenses of the verbs. Translate the sentences paying special attention to the Perfect Tense form of the verbs.

1. Unlike the young mountain belts, which have formed within the last 100 million years, the interiors of the continents have been relatively stable (undisturbed) for the last 600 million years or even longer.

2. During the past 60 years, oceanographers using modern depth-sounding equipment have gradually mapped significant portions of the ocean floor.

3. From these studies they have defined three major regions: continental margins, deep-ocean basins, and oceanic (mid-ocean) ridges.

4. Volcanic activity has also produced several large lava plateaus.

5. The oceanic ridge system consists of layer upon layer of igneous rock that has been fractured and uplifted.

Discussion

Task 1. Read and memorize the following words:

encrust – утворювати тонкий шар	acid - кислота
rupture - проривати, розривати	blast - руйнувати
insulated –ізольований, роз’єднаний	burrowing animals – ті тварини, що риють і живуть у норах
frost wedging – розколювання гірської породи під дією замерзаючих клинів льоду (морозне вивітрювання)	crevice - тріщина
fungus (fungi – мн.) - грибок	exfoliation - сланцюватість, листуватість, шарувата будова
arid - сухий, безводний; посушливий	lichen ['laikən] - лишайник
salt crystal growth – збільшення кристалізації солей	sheeting - пласт, шар; утворення шарів, пластів
expansion - поширення на більшу поверхню	spall off - дробити (породу) ; розбивати (руду) ; обтісувати (камінь)
retain - зберігати	spray - водяний пил

Task 2. Read the text. Translate it into Ukrainian. Talk about the main types of mechanical weathering.

Mechanical Weathering

When a rock undergoes mechanical weathering, it is broken into smaller and smaller pieces, each retaining the characteristics of the original material. The end result is many small pieces from a single large one. In nature, four physical processes are especially important in breaking rocks into smaller fragments: frost wedging, salt crystal growth, expansion resulting from unloading, and biological activity.

Frost Wedging. If you leave a glass bottle of water in the freezer a bit too long, you will find the bottle fractured. The bottle breaks because water has the unique property of expanding about 9% upon freezing. This is also the reason that poorly insulated or exposed water pipes rupture during frigid weather. You might expect this same process to fracture rocks in nature. This is, in fact, the basis for the traditional explanation of frost wedging.

Salt Crystal Growth. Another expansive force that can split rocks is created by the growth of salt crystals. Rocky shorelines and arid regions are common settings for this process. It begins when sea spray from breaking waves or salty groundwater penetrates crevices and pore spaces in rock. As this water evaporates, salt crystals form. As these crystals gradually grow larger, they weaken the rock by pushing apart the surrounding grains or enlarging tiny cracks.

Sheeting. When large masses of igneous rock, particularly granite, are exposed by erosion, concentric slabs begin to break loose. The process generating these onionlike layers is called sheeting. It is thought that this occurs, at least in part, because of the great reduction in pressure when the overlying rock is eroded away, a process called unloading. Accompanying this unloading, the outer layers expand more than the rock below and thus separate from the rock body. Continued weathering eventually causes the slabs to separate and spall off, creating exfoliation domes.

Biological Activity. Both mechanical and chemical weathering are accomplished by the activities of organisms. Plant roots in search of minerals and water grow into fractures, and as the roots grow, they wedge the rock apart. Burrowing animals further break down the rock by moving fresh material to the surface, where physical and chemical processes can more effectively attack it. Of course, where rock has been blasted in search of minerals or for construction, the impact of humans is particularly noticeable.

There are numerous ways that organisms play a role in chemical weathering. For example, plant roots, fungi, and lichens that occupy fractures or may encrust a rock produce acids that promote decomposition. Moreover, some bacteria are capable of extracting compounds from minerals and using the energy from the compound’s chemical bonds to supply their life needs. These primitive “mineral-eating” life forms can live at depths as great as a few kilometers.

Task 3. Compare and discuss the most important types of mechanical weathering:

• frost wedging;

• salt crystal growth;

• sheeting;

• biological activity.

Task 4. Look at Figure 9.2. What type of mechanical weathering does it illustrate? What made you come to that conclusion?