My Science School

          A body of water falling down from a mountain rock is known as a waterfall. If water falls from a great height in the form of a large stream, it is called a cataract. But if the falling stream is narrow, it is called a cascade.

          It is essential for the formation of a waterfall that water flows through certain hard rocky areas. Hard rocks should be followed by soft soil which water can easily cut through. At some places, due to natural changes, the river flows through areas which are higher than the sea level and thus water falls from a height. Sometimes flow of the river is obstructed by landslides. Water accumulates there and later falls down in the form of a waterfall. There are many kinds of waterfalls at many hilly places.

             The Angel waterfall of Venezuela in South America is the highest waterfall of the world. Here water falls from a height of 1000 metres. This was discovered in 1835 by Jimmy Angel, pilot of the US.

            The highest waterfall of Asia is the Gersoppa waterfall in India. The Niagara waterfall is also world-famous for many reasons. Situated 25 km Northwest of New York in the U.S.A., this waterfall of Niagara River is divided into two parts. One part is in the possession of the U.S.A., while the other is in possession of Canada. This waterfall actually acts as the international boundary between these two countries.

            The Ribbon waterfall of California in America is the highest narrow-stream waterfall of the world. A narrow stream falls into the Merced River from a height of 490 metres. The widest waterfall of the world is the Khoni waterfall having a width of 11 km.

            Some waterfalls have proved very useful to man. Hydro-electricity produced from waterfalls is used for innumerable purposes. 

            Glacier is a large mass of moving ice. We see glaciers in various mountain ranges and vallies of the world. In the Alps alone there are as many as 1,200 glaciers. In the high mountains of the Alaska, there are around thousands of glaciers with length, ranging from 30 to 60 kilometres.

            The process for the formation of glaciers is described below. During snowfall snow slides down on the slopes of mountains. After a considerable time it accumulates in big quantities. As this accumulated snow does not melt even in summers, its quantity keeps on increasing. As the quantity of snow increases, the pressure on the lowest layer of the snow also increases. Due to the increased pressure and other atmospheric effects, air leaks out from the lowest layer of snow and consequently, it becomes hardened. This process goes on till a time comes when glaciers become heavy enough to flow downhill under their own weight.

            Glaciers are mainly of two kinds. The first type is the valley glaciers. When there is snowfall on the mountains, the snow slides down on the slopes. This gets deposited in the spaces between the mountains. When snow accumulates in big quantities, it often starts sliding down. The slow moving river of ice is called the valley glacier. Large chunks of stones coming in the way of this river move forward with this river and break into pieces due to friction and collisions with other stones. They spread uniformly in all directions. The motion of the glacier thus forms valleys.

 

Continue reading "What are glaciers? "

       Everybody knows that sea water is salty. This means that some salt in the dissolved form is present in sea water. One gallon of sea water contains about one hundred grams of salt. In general sea water has 4% to 6% salt in it. In comparison to open seas, the quantity of salt in closed seas like the Mediterranean and the Red Sea is more. If salt of all the oceans is collected and dried, one can make a 288 km high and 1.6 km thick wall with this salt, which will be long enough to encircle the entire perimeter of the Earth along the equator.

 

Continue reading "Why is the sea water salty? "

         About three-fourth of the Earth’s total surface is covered with water. Only one-fourth of Earth’s surface is land. The total area of the Earth’s surface covered by oceans comes to 361.100 million sq. km. Do you know how and when these oceans were formed?

          It is not yet fully known when oceans were formed. However, at the beginning of the formation of Earth, there were no oceans. The age of oceans has been calculated on the basis of the minerals present inside them. It is estimated that oceans were formed some time between 500 to 1,000 millions years before.

            The story of the origin of oceans is very interesting. The Earth was a giant burning fire ball at the time of its birth. Its surface was formed by molten rocks. When the Earth started cooling slowly, it was enveloped by clouds of gases. These clouds became very heavy after cooling. They started raining heavily, but the Earth’s surface was still so hot that the raindrops falling on it would evaporate and mix with the atmosphere again. This would again come down to the Earth in the form of rains. This cycle continued for millions of years. The Earth’s crust became cold and tough and the rain-water would boil no more, but the heavy down-pour continued for thousands of years. The low-lying areas of the Earth were filled up with the water of these heavy rains. These vast lakes of water on the surface of the Earth are today’s oceans. 

          Dead Sea is the only sea on earth which has no plant or animal life. It is, therefore, appropriately called Dead Sea. In fact, Dead Sea is a saline lake situated between Jordan and Israel. This is 77 km long and its breadth ranges between 5 to 18 kilometres. The water level of Dead Sea is the lowest on the Earth. It is lower than the sea-level by 396 metres. Millions of years ago the level of Dead Sea was, however, higher than the present one by 427 metres. At that time aquatic animals were living in Dead Sea. All of a sudden, there was a draught and the water of this sea evaporated. Gradually this sea acquired the present state.

          No river originates from this sea. The Jordan River and some small canals end up in this sea. Since no river comes out of this, the water of this sea depletes only by evaporation. Consequently, the amount of salt and other soluble minerals brought into the sea by the Jordan River and other smaller canals goes on increasing. You will be surprised to know that the amount of salt present in Dead Sea is the largest in comparison to the other seas. In general, the amount of salt present in any sea is 4% to 6%. But even this make you sick as it contains large quantities of magnesium chloride and other poisonous substances. Due to the presence of large quantities of salt and other poisonous materials no living being can survive in this sea. Hence fish and other acquatic animals of the Jordan River die as soon as they enter the water of this sea.

 

          Generally, Sea Mountains are those mountains which are at least one kilometre above the seabed. A number of such mountains have been discovered.

          Upheavals at the bottom of the sea are responsible for the formation of these mountains. Volcanic eruptions in the seabed also make mountains. Generally, these mountains are one to three kilometres high. Majority of these mountains remain submerged in water, but some of them have surfaced above also. The flat mountains coming above water are called islands. The Hawaii islands were formed in this manner.

          There are many mountains in the midst of oceans. The mid-ocean ridge is continuous and it winds for 60,000 km through all worlds’ oceans. There are many mountains in the north-east part of the Pacific Ocean. Most of these mountains are submerged in water, but some of the mountains of the Hawaiian chain have surfaced above. They are called the Hawaii Islands. The highest mountain of the Hawaiian chain is the Mauna Kea. The height of this mountain is 4,200 metres above sea level, but the total height of this mountain from the bottom of the sea is 9,686 metres. That means the height of this mountain inside the sea is 5,486 metres. If its height is taken in full, this is the highest mountain of the world. 

           The word monsoon is used to connote a seasonal wind which flows with consistency and regularity for one part of the year and blows from the other direction for the other part of the year.

            Monsoon rains are generated over different parts of the world due to the difference in response of land and sunlight and the resulting wind movement.

            Over land, as a consequence of chemical composition and structure of the soil, only a few centimeters of the soil is heated by sunlight. But as the air has a low heat capacity, the atmosphere gets heated up rapidly.

            On the other hand, the sea is warmed up slowly because of its larger heat capacity and also because sunlight penetrates up to 200 m into the water. Hence the air above the oceans remains cooler. The temperature difference between them lies in the range of 5-10 degrees Centigrade.

            As a consequence of this, the warmer air over land begins to rise. To compensate this ascending air the denser air from the ocean has to move towards the land. (This is commonly known as sea breeze). This differential heating is the driving force for the monsoon winds.

            During the northern summer (summer in the northern hemisphere) the sun is over the Tropic of Cancer (23.5 degrees). In this period the land in the northern hemisphere gets warmed up while the southern hemisphere is cooler as it receives less sunlight.

            The land-sea contrast is much more in rectangular region shown in the figure than any other part of the world. Due to differential heating, the cooler moist air from the southern hemisphere starts moving towards the hot northern hemisphere. Once this airflow (called Somali current because it flows along the coast of Somali and Kenya region) crosses the equator the Coriollis force (a force arising due to the rotation of the Earth) turns the air to its right (in the Northern hemisphere). This flows over India and East Asia from the South West direction (hence the name south west monsoon). This moist air when aided by other factors results in abundant rain.

            The Tibet Plateau on the Himalayas acts as a potential heat source for this kind of air movement. The lifetime of south-west monsoon is about 100 days which starts early June and ends by mid September. The arrival of monsoon is a gradual process starting with a transition period when the atmospheric characteristics change from a state of extreme dryness to high humidity and slight rainfall. Thunderstorm is a feature of pre-monsoon months of April and May over North-East India.

Ultrasonic sounds are used to measure the depth of oceans and the principle behind is known as sound navigation and ranging, Sonar. Ultrasonic waves are sent from a transmitter from the surface of the sea, from a ship.

            The sound waves are reflected by the sea bottom are sensed be a receiver system and recorded. With the known value of the speed of sound in water, and the time taken by the sound to travel from the surface to the bottom and back, the depth is measured.

In the beginning, the Earth's atmosphere was made up of only nitrogen, carbon dioxide, and some hydrogen. There was very little oxygen present, and it was produced by stromatolites- which are rocks formed by the growth of blue green algae- strewn in the sea. Whatever oxygen was present was quickly absorbed by rocks and minerals. Gradually however, excess oxygen began to accumulate in the atmosphere. This excess oxygen had a dramatic effect on the living cells present. It triggered the evolution of a higher form of life. These were nucleus-containing eukaryotic cells. Thus, the simple blue green algae that were the first form of life became stepping stones to higher life forms, thanks to rising oxygen levels in the atmosphere.

The Precambrian Period spans a long period of the Earth's history. It starts with the planet's creation about 4.5 billion years ago, and ends with the emergence of complex, multicelled life-forms almost four billion years later. It is extremely significant, because it is the earliest of the geologic ages which are marked by different layers of sedimentary rock. Laid down over millions of years, these rock layers contain a permanent record of the Earth's past, including the fossilized remains of plants and animals buried when the sediments were formed.The Precambrian is divided into two parts- the Archaean time, and the Proterozoic Era. There may not have been many different forms of life, but very important changes were taking place during the Precambrian. The Earth was formed, and its outer covering cooled and hardened into a crust. The hot molten insides of the Earth leaked out at weak places in the crust to form volcanoes. The clouds formed by the volcanoes caused huge amounts of rain to fall, and the oceans were created.The first life formed. The oceans were like a thick soup, and their chemistry made them the perfect place for life to begin. The first one-celled organisms formed during the Precambrian Era. They had an important job to do. They helped make the air and water around the Earth full of oxygen. Once there was plenty of oxygen, new life could form. This life would have many cells which would evolve into different kinds of animals. All of the important work of the Precambrian period made the Earth ready for what would come next.

Which Way Up?

            Hallucigenia was a bizarre looking fossil which appeared to have tentacles on its back. For a long time, scientists were baffled by it, and unable to determine what kind of creature it was. Finally, they realized that they were looking at it upside down! The tentacles were in fact, legs that resembled the tubular legs of today’s velvet worms!

The Archaean Period lasted from 3800 to 2500 million years ago. The Earth was still about three times as hot as it is today, and most of its area was covered with oceans. The Earth’s atmosphere was mainly carbon dioxide, with very little oxygen in it. Land was beginning to form as volcanoes that emerged from the oceans. The forming of the continents also began during this period, probably as lava flow under the ancient oceans.About this time, the earliest living cells formed on Earth. These cells all lived in the oceans. One type of bacteria present then was the cyanobacteria, or blue-green algaes. These bacteria appear to have had a very strong cell-wall, and the ability to form layers in the ancient sediments. The formations are called stromatolites. They can be found in Archaean rock formations of Western Australia.So to sum up, the Archaean Period was a time of continent-building, and the first stages of early life can be traced back to this period. 

Raising Rocks

            Do you know why you sometimes find sea shells on top of rocks? It is because most sedimentary rocks were once found under the sea. Animals that were buried in the sediment became fossilized. Later, movements of the Earth’s crust resulted in the sea bed being pushed upward, and rocks that had been under the sea now became mountain tops.

People often think of fossils as being mineralized bones or shells stored in museums. However, they can even be any remains or traces of ancient organisms. They can ever be footprints, burrows, or casts of bodies, with nothing else surviving. Interpreting fossils is sometimes like solving a jigsaw puzzle.One of the ways of interpreting a fossil to compare the fossil with the skeleton of a living creature that seems to resemble it. For example, there are many well preserved fossils of coiled shell of ammonites, which are an extinct group of marine animals with no backbone. However, the soft body parts of these animals have not been preserved. But the fossils can be reconstructed, because a modern marine species known as the nautilus is very similar to the ammonites. So, in this case, interpretation is possible. When only one or two skeletons of a species have been discovered, there is no way of interpreting them correctly. For example, in the case of a dinosaur fossil, what was once interpreted as being a horn is now believed to be a large pointed thumb? So, until many similar specimens have been found, it is unwise to attempt a species description

The Tay Rail Bridge was completed in February 1878 to the design of Thomas Bouch. At that time, it was the longest bridge in the world. Less than two years later, at approximately 7:15 p.m. on the stormy night of 28th December 1879, the central navigation spans of the Tay bridge collapsed into the Firth of Tay at Dundee, taking with them a train, 6 carriages and killing 75 passengers.

Another famous bridge collapse was that of the Tacoma Narrows Bridge (USA). It was revolutionary in its collapse. This bridge was known for its tendency to sway in windstorms. The shape of the bridge was much like that of an aircraft wing and under windy conditions, it would rise and fall likes the movement of a galloping horse. On November 7th, 1940 a large windstorm turned the galloping motion into uncontrolled bucking, and the bridge collapsed.

There have been several other bridges that have collapsed. On October 17th 1989, several bridges in San Francisco, USA, collapsed as the result of an earthquake. Bridges are marvels of engineering, but when they collapse, the marvel turns into a tragedy with terrible consequences.

Fossils form when an animal or plant dies in water or nearby places. The water insulates the remains from many of the elements that contribute to decomposition. For example, when an animal has died of old age at the bottom of the sea, bacteria consume the soft body parts, but leave the hard exoskeleton intact. As time passes, sediments bury the exoskeleton. As the sediments continue to pile on, the lower layers become compacted by the weight of the layers on top. Over time, this pressure turns the sediments into rock. As the continental plates move around the Earth, crashing into each other, mountains are formed. Former sea floors are lifted up, and become dry land. Thanks to the movement of the plates, fossils will come closer to the surface and nearer to discovery by some fortunate fossil hunter. Fossils are finally revealed through the forces of erosion.Though there are millions of fossils that have been discovered and millions more waiting to be discovered, fossilization is a rare occurrence. Soft bodied animals and plants that have no woody parts are rarely fossilized.

Paleontology is the study of fossils. Paleontology has played a key role in developing the theory of evolution. The study of fossils has shown that the animals and plants of prehistoric times were very different indeed from the animals and plants of today. By reassembling fossils bones, scientists can get an idea of the size and shape of the creatures that inhabited the Earth before the appearance of humans. Teeth and shells that have been fossilized also tell us much about the lifestyle of these creatures. Fossils of insects are often found embedded in amber, which is a transparent rock nodule formed when the resin from trees petrifies. Small creatures are sometimes trapped inside the amber, and are perfectly preserved to give us a glimpse of ancient insects.Trace fossils are also important in the study of evolution. Trace fossils are tunnels, worm casts and tracks that animals have made on soft sediment that has later hardened into rock. These imprints of animals on the move reveal much about the lives of ancient species, including their size, gait, stride length, and speed.