1. The same thing happens to this day, though on a smaller scale, wherever asediment-laden river or stream emerges from a mountain valley onto relatively flat land,dropping its load as the current slows: the water usually spreads out fanwise, depositingthe sediment in the form of a smooth, fan-shaped slope.
2. Sediments are also dropped where a river slows on entering a lake or the sea, thedeposited sediments are on a lake floor or the seafloor at first, but will be located inlandat some future date, when the sea level falls or the land rises; such beds are sometimesthousands of meters thick.
3. In lowland country almost any spot on the ground may overlie what was once the bedof a river that has since become buried by soil; if they are now below the water’s uppersurface (the water table), the gravels and sands of the former riverbed, and its sandbars,will be saturated with groundwater.
4. This is because the gaps among the original grains are often not totally plugged withcementing chemicals; also, parts of the original grains may become dissolved bypercolating groundwater, either while consolidation is taking place or at any timeafterwards.
5. But note that porosity is not the same as permeability, which measures the ease withwhich water can flow through a material; this depends on the sizes of the individualcavities and the crevices linking them.
6. If the pores are large, the water in them will exist as drops too heavy for surface tensionto hold, and it will drain away; but if the pores are small enough, the water in them willexist as thin films, too light to overcome the force of surface tension holding them inplace; then the water will be firmly held.
1. The extreme seriousness of desertification results from the vast areas of land and the tremendous numbers of people affected, as well as from the great difficulty of reversing or even slowing the process.
2. In areas where considerable soil still remains, though, a rigorously enforced programof land protection and cover-crop planting may make it possible to reverse the present deterioration of the surface.
TPO2：The Origins of Cetaceans
1. However, unlike the cases of sea otters and pinnipeds (seals, sea lions, and walruses, whose limbs are functional both on land and at sea), it is not easy to envision what the first whales looked like.
2. The structure of the backbone shows, however, that Ambulocetus swam like modern whales by moving the rear portion of its body up and down, even though a fluke was missing.
1. In order for the structure to achieve the size and strength necessary to meet its purpose, architecture employs methods of support that, because they are based on physical laws,have changed little since people first discovered them—even while building materials have changed dramatically.
2. The arch was used by the early cultures of the Mediterranean area chiefly for underground drains, but it was the Romans who first developed and used the arch extensively in aboveground structures.
TPO3：Depletion of the Ogallala Aquifer
1. Estimates indicate that the aquifer contains enough water to fill Lake Huron, but unfortunately, under the semiarid climatic conditions that presently exist in the region, rates of addition to the aquifer are minimal, amounting to about half a centimeter a year.
2. This unprecedented development of a finite groundwater resource with an almost negligible natural recharge rate—that is, virtually no natural water source to replenish the water supply—has caused water tables in the region to fall drastically.
3. The incentive of the farmers who wish to conserve water is reduced by their knowledge that many of their neighbors are profiting by using great amounts of water, and in the process are drawing down the entire region’s water supplies.
TPO4：Cave Art in Europe
1. The researchers Peter Ucko and Andree Rosenfeld identified three principal locations of paintings in the caves of western Europe: (1) in obviously inhabited rock shelters and cave entrances; (2) in galleries immediately off the inhabited areas of caves; and (3) in the inner reaches of caves, whose difficulty of access has been interpreted by some as a sign that magical-religious activities were performed there.
2. Perhaps, like many contemporary peoples, Upper Paleolithic men and women believed that the drawing of a human image could cause death or injury, and if that were indeed their belief, it might explain why human figures are rarely depicted in cave art.
3. Consistent with this idea, according to the investigators, is the fact that the art of the cultural period that followed the Upper Paleolithic also seems to reflect how people got their food.
TPO4：Deer Populations of the Puget Sound
1. Wildlife zoologist Helmut Buechner(1953), in reviewing the nature of biotic changes in Washington through recorded time, says that "since the early 1940s, the state has had more deer than at any other time in its history, the winter population fluctuating around approximately 320,000 deer (mule and black-tailed deer), which will yield about 65,000 of either sex and any age annually for an indefinite period."
2. In addition to finding an increase of suitable browse, like huckleberry and vine maple,Arthur Einarsen, longtime game biologist in the Pacific Northwest, found quality of browse in the open areas to be substantially more nutritive.
TPO5: Minerals and Plants
1. Mineral deficiencies can often be detected by specific symptoms such as chlorosis (loss of chlorophyll resulting in yellow or white leaf tissue), necrosis (isolated dead patches), anthocyanin formation (development of deep red pigmentation of leaves or stem), stunted growth, and development of woody tissue in an herbaceous plant.
2. Only recently have investigators considered using these plants to clean up soil and waste sites that have been contaminated by toxic levels of heavy metals–an environmentally friendly approach known as phytoremediation.
3. For examples, in field trials, the plant alpine pennycress removed zinc and cadmium from soils near a zinc smelter, and Indian mustard, native to Pakistan and India, has been effective in reducing levels of selenium salts by 50 percent in contaminated soils.
TPO5: The Origin of the Pacific Island People
1. Contrary to these theorists, the overwhelming evidence of physical anthropology, linguistics, and archaeology shows that the Pacific islanders came from Southeast Asia and were skilled enough as navigators to sail against the prevailing winds and currents.
2. The basic cultural requirements for the successful colonization of the Pacific islands include the appropriate boat-building, sailing, and navigation skills to get to the islands in the first place, domesticated plants and gardening skills suited to often marginal conditions, and a varied inventory of fishing implements and techniques.
3. Contrary to the arguments of some that much of the pacific was settled by Polynesiansaccidentally marooned after being lost and adrift, it seems reasonable that this feat was accomplished by deliberate colonization expeditions that set out fully stocked with food and domesticated plants and animals.
4. As Patrick Kirch, an American anthropologist, points out, rather than being brought by rafting South Americans, sweet potatoes might just have easily been brought back by returning Polynesian navigators who could have reached the west coast of South America.
TPO6: Powering the Industrial Revolution
Only the last of these was suited at all to the continuous operating of machines, and although waterpower abounded in Lancashire and Scotland and ran grain mills as well as textile mills, it had one great disadvantage: streams flowed where nature intended them to, and water-driven factories had to be located on their banks whether or not the location was desirable for other reasons.
2. Early in the eighteenth century, a pump had come into use in which expanding steam raised a piston in a cylinder, and atmospheric pressure brought it down again when the steam condensed inside the cylinder to form a vacuum.
3. This “atmospheric engine,” invented by Thomas Savery and vastly improved by his partner, Thomas Newcomen, embodied revolutionary principles, but it was so slow and wasteful of fuel that it could not be employed outside the coal mines for which it had been designed.
4. Another generation passed before inventors succeeded in combining these ingredients,by putting the engine on wheels and the wheels on the rails, so as to provide a machine to take the place of the horse.
TPO6: William Smith
1. In 1815 he published the first modern geological map, “A Map of the Strata of England and Wales with a Part of Scotland,” a map so meticulously researched that it can still be used today.
2. But as more and more accumulations of strata were cataloged in more and more places, it became clear that the sequences of rocks sometimes differed from region to region and that no rock type was ever going to become a reliable time marker throughout the world.
3. Not only could Smith identify rock strata by the fossils they contained, he could also see a pattern emerging: certain fossils always appear in more ancient sediments, while others begin to be seen as the strata become more recent.
4. Limestone may be found in the Cambrian or—300 million years later—in the Jurassic strata, but a trilobite—the ubiquitous marine arthropod that had its birth in the Cambrian—will never be found in Jurassic strata, nor a dinosaur in the Cambrian.