+Earth+(10000x5000).jpg)
Have a look of our beautiful world...It's beautiful indeed.
Save this beautiful world, show your care towards it.
Stop CFC releasing gadgets/machines.
Use bicycles to cover near by distances.
May it not happen that you don't see the polar area in the above picture depleted in the near future.......
So,
Prevent Global Warming.
Join hands together to save our Mother Earth
Present Harms of Global Warming
Sea level is currently rising at about 2 millimeters (0.08 inch) per year. Between 0.2 and 0.6 millimeter per year has been attributed to thermal expansion of ocean water, and most of the remainder is thought to be caused by the melting of glaciers and ice sheets on land. There is concern that the rate in sea-level rise may increase markedly in the future owing to global warming. Unfortunately, the state of the mass balance of the ice on the Earth is poorly known, so the exact contributions of the different ice masses to rising sea level is difficult to analyze. The mountain (small) glaciers of the world are thought to be contributing 0.2 to 0.4 millimeter per year to the rise. Yet the Greenland Ice Sheet is thought to be close to balance, the status of the Antarctic Ice Sheet is uncertain, and, although the floating ice shelves and glaciers may be in a state of negative balance, the melting of floating ice should not cause sea level to rise, and the grounded portions of the ice sheets seem to be growing. Thus, the cause of sea-level rise is an enigma.
With global warming, the melting of mountain glaciers will certainly increase, although this process is limited: the total volume of small glaciers is equivalent to only about 0.6 meter (2 feet) of sea-level rise. Melting of the marginal areas of the Greenland Ice Sheet will likely occur under global warming conditions, and this will be accompanied by the drawing down of the inland ice and increased calving of icebergs; yet these effects may be counterbalanced to some extent by increased snow precipitation on the inland ice. The Antarctic Ice Sheet, on the other hand, may actually serve as a buffer to rising sea level: increased melting of the marginal areas will probably be exceeded by increased snow accumulation due to the warmer air (which holds more moisture) and decreased sea ice (bringing moisture closer to the ice sheet). Modeling studies that predict sea-level rise up to the time of the doubling of greenhouse gas concentrations (i.e., concentrations of atmospheric carbon dioxide, methane, nitrous oxide, and certain other gases) about the year 2050 suggest a modest rise of about 0.3 meter (1 foot).
Information from deep cores
Most of the Antarctic Ice Sheet and much of the Greenland Ice Sheet are below freezing throughout. Continuous cores, taken in some cases to the bedrock below, allow the sampling of an ice sheet through its entire history of accumulation. Records obtained from these cores represent exciting new developments in pale o climatology and paleoenvironmental studies. Because there is no melting, the layered structure of the ice preserves a continuous record of snow accumulation and chemistry, air temperature and chemistry, and fallout from volcanic, terrestrial, marine, cosmic, and man-made sources. Actual samples of ancient atmospheres are trapped in air bubbles within the ice. This record extends back more than 300,000 years.
Near the surface it is possible to pick out annual layers by visual inspection. In some locations, such as the Greenland Ice core Project/Greenland Ice Sheet Project 2 (GRIP/GISP2) sites at the summit of Greenland, these annual layers can be traced back more than 40,000 years, much like counting tree rings. The result is a remarkably high-resolution record of climatic change. When individual layers are not readily visible, seasonal changes in dust, marine salts, and isotopes can be used to infer annual chronologies. Precise dating of recent layers can be accomplished by locating radioactive fallout from known nuclear detonations or traces of volcanic eruptions of known date. Other techniques must be used to reconstruct a chronology from some very deep cores. One method involves a theoretical analysis of the flow. If the vertical profile of ice flow is known, and if it can be assumed that the rate of accumulation has been approximately constant through time, then an expression for the age of the ice as a function of depth can be developed.
A very useful technique for tracing past temperatures involves the measurement of oxygen isotopes—namely, the ratio of oxygen-18 to oxygen-16. Oxygen-16 is the dominant isotope, making up more than 99 percent of all natural oxygen; oxygen-18 makes up 0.2 percent. However, the exact concentration of oxygen-18 in precipitation, particularly at high latitudes, depends on the temperature. Winter snow has a smaller oxygen-18–oxygen-16 ratio than does summer snow. A similar isotopic method for inferring precipitation temperature is based on measuring the ratio of deuterium ( hydrogen-2) to normal hydrogen (hydrogen-1). The relation between these oxygen and hydrogen isotopic ratios, termed the deuterium excess, is useful for inferring conditions at the time of precipitation. The temperature scale derived from isotopic measurements can be calibrated by the observable temperature-depth record near the surface of ice sheets.
Results of ice core measurements are greatly extending the knowledge of past climates. For instance, air samples taken from ice cores show an increase in methane, carbon dioxide, and other “greenhouse gas” concentrations with the rise of industrialization and human population. On a longer time scale, the concentration of carbon dioxide in the atmosphere can be shown to be related to atmospheric temperature (as indicated by oxygen and hydrogen isotopes)—thus confirming the global-warming greenhouse effect, by which heat in the form of long-wave infrared radiation is trapped by atmospheric carbon dioxide and reflected back tothe Earth's surface.
Perhaps most exciting are recent ice core results that show surprisingly rapid fluctuations in climate, especially during the last glacial period (160,000 to 10,000 years ago) and probably in the interglacial period that preceded it. Detectable variations in the dustiness of the atmosphere (a function of wind and atmospheric circulation), temperature, precipitation amounts, and other variables show that, during this time period, the climate frequently alternated between full-glacial and nonglacial conditions in less than a decade. Some of these changes seem to have occurred as “flickerings,” in which the temperature jumped 5° to 7° C (9° to 13° F), remained in that state for a few years, jumped back, and repeated the process several times before settling into the new state for a long time—perhaps 1,000 years. These findings have profound and unsettling implications for the understanding of the coupled ocean-atmosphere climate system.
Freeze-up
The first appearance of lake ice follows by about one month the date at which the long-term average daily air temperature first falls below freezing. Ice appears first in smaller shallow lakes, often forming and melting several times in response to the diurnal variations in air temperature, and finally forms completely as air temperatures remain below the freezing point. Larger lakes freeze over somewhat later because of the longer time required to cool the water. In North America the Canadian-U.S. border roughly coincides with a first freeze-up date of December 1. North of the border freeze-up occurs earlier, as early as October 1 at Great Bear Lake in Canada's Northwest Territories. To the south the year-to-year patterns of freeze-up are ever more erratic until, at latitudes lower than about 45° N, freeze-up may not occur in some years.
In Europe the freeze-up pattern is similar with respect to air temperatures, but the latitudinal pattern shows more variation because much of western Europe is affected by the warming influence of the Gulf Stream. In Central Asia the latitudinal variation is more regular, with first freeze-up occurring about mid-January at 45° N and about October 1 at72° N. Exceptions to these patterns occur where there are variations in local climate and elevation.
Clearing
Because of the time required to melt ice that has thickened over the winter, the clearing of lake ice occurs some time after average daily air temperatures rise above freezing. Typically the lag is on the order of one month at latitude 50° N and about six weeks at 70° N. This pattern results in average clearing dates in mid-April at the U.S.-Canadian border and in June and July in the northern reaches of Canada.
Permian life
Life during the Permian was very diverse, and the marine life of the period was perhaps morediverse than that of modern times. The previous period, the Carboniferous, had had two instances of significant marine faunal extinctions that had followed one another in relatively rapid succession. One was at the end of the Early Carboniferous (Mississippian subperiod in North America) and the other at the end of the Middle Carboniferous (the close of the Middle Pennsylvanian). Both may be attributed to global cooling during continental glaciations. The latest Carboniferous witnessed the establishment of new or highly modified marine lineages with relatively little ecological competition from the remnants of what had been highly successful earlier phylogenetic lineages. Most of these lineages are identified as new families or suborders among the foraminifers, ammonoids, brachiopods, bryozoans, bivalves, and some less-studied groups. In Wolfcampian, Leonardian, and Guadalupian times, these newly established lineages underwent rapid evolution and filled a remarkable number of specialized marine ecological niches. Some of this rapid diversification was probably the result of filling the ecological niches left vacant by the extinctions of the Carboniferous. Other factors undoubtedly included the gradual warming of oceans during the latest Carboniferous and the more rapid warming trends of the Early Permian. In paleotropical areas, a succession of carbonate bank, bioherm,and reef faunal associations evolved, which culminated in the late Guadalupian Capitan Reefs of the western United States and the more faunally diverse associations that formed even thicker fringing reefs in the Tethyan area. Because these two sets of tropical marine shallow-water faunal associations were separated by the large supercontinent Pangaea on the one hand and the deep oceanic basin of Panthalassa on the other,they tended to evolve independently of each other.
Extinctions
Near the end of the Guadalupian both of the these tropical faunal realms suffered major but incomplete extinctions, and the Djulfian saw a brief and relatively minor evolutionary re-expansion in some of the foraminifers and ammonoids. Thetrilobites were extinct by the end of the Leonardian. Only a few Permian bryozoan and brachiopod genera, and only one or two species of those genera, survived into the earliest Triassic. Although the magnitude of the extinctions among shallow-water marine organisms during the later parts of the Permian was great, the process took several million years and was accomplished in a series of steps followed by unsuccessful attempts by the surviving faunas to rediversify.
Terrestrial life in the Permian was closely keyed to the evolution of terrestrial plants, which of course were the primary food source for terrestrial animals. The fossil plant record for the Permian consists predominantly of ferns, seed ferns, and lycophytes, which is attributable to their adaptation to marshes and swampy environments. A less abundant fossil record of early coniferophytes and even some protoangiosperms suggests a broad adaptation of these plantgroups to progressively drier areas. As discussed earlier, evidence seems to point to gradually warming and drier climates, which would have encouraged plant adaptations to drier conditions.
Another line of evidence suggesting broad plant diversification is found in the evolution of insects; these animals tend to be highly selective in choosing their plant hosts. Among the superclass Hexapoda of the phylum Arthropoda, at least 23 orders are known from the Permian, and of these orders 11 are extinct. By comparison, 250 million years later, there exist only 28 insect orders, and the new orders are mainly those that have adapted to living on the angiosperms or mammals that evolved after Permian time. Permian insects include a huge dragonfly-like creature that had a wingspan of 75 centimeters.
Emergence of important reptiles
Terrestrial vertebrates of the Permian, in addition to freshwater sharks and fish and several orders of relatively largeamphibians, are noted for the first appearance of several important reptile lineages. Although a few primitive and generalized reptile fossils are found in Middle Carboniferous deposits, Permian reptile fossils are locally common and include the protorosaurs, aquatic reptiles; the captorhinomorphs,the “stem reptiles” from which most other reptiles are thought to have evolved; the eosuchians, early ancestors of the snakes and lizards; early anapsids, ancestors of turtles; early archosaurs, ancestors of the large ruling reptiles of the Mesozoic; and the synapsids, a common and varied group of mammal like reptiles that eventually gave rise to mammals in the Mesozoic. Of these, the captorhinomorphs and synapsids are probably the best known.
Captorhinomorphs are common in the Lower Permian beds of North America and Europe. Massively built and large for their day, they reached lengths of two to three meters. Captorhinomorphs are less common in Upper Permian beds, and only one small group survived into the Triassic.
Synapsids are divided into two orders: the pelycosaurs and the therapsids. The Early Permian pelycosaurs included a lineage containing both carnivorous and herbivorous members that developed long spines on their vertebrae, which seem to have supported a membrane, or “sail.” The function of the sail is not fully understood; however, suggestions include its use in regulating body temperature. Pelycosaurs reached 3.5 meters in length and had large teeth. Their remains are commonly found in the Lower Permian red beds of central Texas but are rare in Europe.
The therapsids were advanced synapsids that are known from the Upper Permian Karoo beds of South Africa, South America, and India and equivalent beds in Scotland and what was formerly the Soviet Union. Therapsids range into the Triassic and show a great deal of diversification. Their dentition and bone structure are remarkably mammal like, and the point at which a mammal like reptile passes into an actual mammal has long been a point of controversy. The success of therapsids in the relatively high paleolatitudes of Gondwana has strengthened the view that they were able to maintain an elevated body temperature.
These were some important points that I considered to convey to you. Hope these might be useful
.jpg)
.jpg)
.jpg)
+Earth+(10000x5000).jpg)