Category Science

                      Our atmosphere is the protective covering over the earth. Although there are no perceivable layers or distinguishable boundary marks, the atmosphere can be divided into layers for the sake of comprehension. The atmosphere comprises of five layers: the troposphere, the stratosphere, the mesosphere, thermosphere and the exosphere.

                    Animals and plants live in the troposphere. This is because this layer is rich in oxygen, which is an indispensable element for the survival of life. The troposphere be-gins at the surface of the earth and extends to between 7 km at the poles and 17 km at the equator. The tropopause is the boundary between the troposphere and stratosphere.

                        The next layer is called stratosphere and it extends from the tropopause to about 51 km upwards. The stratopause, which is the boundary between the stratosphere and mesosphere, typically is at 50 to 55 km. The mesosphere extends from the stratopause to 80-85 km. It is in this layer where most meteors burn up upon entering the atmosphere.

                        The top of the thermosphere is the bottom of the exosphere, called the exobase. The height of exosphere varies with solar activity and ranges from about 250 to 800 km. The outermost layer of Earth’s atmosphere is called exosphere.

              In the biting cold of a winter morning, we would prefer to lie curled up, wrapping ourselves in the comfort of a thick blanket. If necessity compels us to get out of our home, we would wear a pullover to warm ourselves. The pullover and blanket help us keep the chill at bay. While Man has invented clothing to adapt to the change of seasons and climate, our earth has a natural blanket called atmosphere.

              Atmosphere protects our planet from harmful ultraviolet rays of the sun. It acts like a blanket around the earth. It not only protects our planet from the sun but also provides the conditions necessary for the sustenance of life on Earth. Life exists on Earth because of atmosphere.

              Dry air in the atmosphere consists of 78 per cent nitrogen, 21 per cent oxygen, 1 per cent argon and other inert gases, such as carbon dioxide. Other than these gases, there are many other gases in the atmosphere too. The ozone layer of the earth’s atmosphere plays an important role in preventing the ultraviolet (UV) radiation from reaching the planet’s surface.

            There is a variety of water bodies on earth. They differ from each other in terms of the amount of water they hold, the salinity of water and variety of ecosystems they contain.

            We call a body of water a lake when it is inland and is not part of an ocean, lakes are larger and deeper than a pond and are fed by a river, Natural lakes on Earth are generally found in mountainous area, rift zone and areas with ongoing or recent glaciations. Other lakes are found in basins, which have no connection to seas, or along the courses of mature rivers. In some parts of the world, there are many lakes because of chaotic drainage patterns left over from the last Ice Age. All lakes are temporary over geologic time scales, as they will slowly fill in with sediments or spill out of the basin containing them. Lake Superior is the longest fresh water lake in the world. It is 560 km long with a surface area of 82,100 sq. km. On the other hand, a pond is a body of water that does not flow anywhere. Ponds are either natural or man-made, and are usually smaller than a lake. Ponds and lakes are distinguished from streams by the speed of their currents.

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            Civilizations world over have developed on the banks of great rivers. Our nation derives its name from a river! Rivers have been not only the backbones of civilizations, but also home to many ecosystems.

          Rivers are large natural streams of water flowing into an ocean, a lake or any larger body of water. Unlike oceans, rivers, lakes and waterfalls are freshwater ecosystems. Water within a river is generally collected from precipitation through surface runoff, groundwater recharge, springs, and the release of stored water in natural ice and snow-packs such as glaciers.

            There are several other names to denote smaller rivers, such as stream, creek and brook. Most small rivers and ponds appear only in monsoons, as rain is their main source of water. Therefore, they dry up in summers. Such rivers are called non-perennial rivers. On the other hand, big rivers that contain water throughout the year are called perennial rivers.  

            Streams play an important corridor role in connecting fragmented habitats and thus in conserving biodiversity. The study of streams and waterways in general is known as Surface Hydrology.

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            The deep blue seas have fascinated Man for thousands of years. While Man has conquered even the highest mountain peaks on land, he has not been successful in exploring the oceans fully. Oceans are a very different world!

            Water covers about two-thirds of the earth’s surface. Oceans are the largest ecosystems existing on Earth. Atlantic Ocean, Pacific Ocean, Arctic Ocean, Indian Ocean and Southern Ocean are the five great oceans of the earth. The Pacific and Atlantic may be further subdivided by the equator into northerly and southerly portions.

            Smaller regions of the oceans are known as seas, gulfs and bays. There are also salt lakes, which are smaller bodies of landlocked saltwater. Most of these lakes are not interconnected with the larger oceans. Two notable examples of salt lakes are the Aral Sea and the Great Salt Lake.

            The ocean bed is not plain. There are huge mountains, trenches, ridges and volcanoes under the water. Such diverse landscape underwater makes many different habitats possible.

            Life exists in various forms in oceans. However, the oceans do not contain a large variety of species. Just 20 percent of the species existing on Earth live in the oceans.

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