Mountains



 



 



 



How are mountains formed?



There are three main ways in which mountains can be formed. Volcanoes form mountains when lava from deep inside the Earth cools and hardens on the surface. Other mountains are formed when layers of rock are forced up into folds, or when rocks fracture to cause faults, allowing slabs of rock to be raised up. These movements are caused by the very gradual shifting of the land areas, which sets up stresses in the Earth’s crust. 



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Which are the oldest mountains?



Low, smooth mountain ranges are the oldest. The most recently formed mountains are usually jagged and steep, because their rocks have not been worn away and smoothed by erosion. Over millions of years, the rocks wear away and the shape of the mountains becomes more rounded. ]



Eventually, they may wear away completely. When measured in geological time, most of the world’s mountains are still relatively young. 



 



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Fresh Water



Can water wear away solid rock?



Water itself cannot wear away rock, but tiny particles of grit carried in the water can eventually wear away the hardest rocks. It is this continuous wearing process that cuts valleys through mountains and hills. The faster the water flows, the more the grit it carries wears away at the rock. You can see the same process in action along the coast. There, rocks are worn away by the action of sand dashed against them by the waves. 



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Which is the world’s highest waterfall?



The Angel Falls in Venezuela, South America, fall 807 m in a single drop. Much more water flows over Victoria Falls in southern Africa and Niagara Falls on the US-Canadian border, but these falls are not so high. Waterfalls occur when a river flows over hard rock lying over softer rock. The hard rock forms a ‘lip’ for the waterfall, and the water wears away the softer rock below, forming a step that gradually becomes deeper.



Picture credit: google



 


 



 



Fresh Water



 



What is a spring?



Many types of rock contain tiny holes like a sponge, in which rainwater collects. The water gradually sinks down and eventually flows out lower down. Water stored in such porous rocks sometimes bubbles to the surface in springs. They are usually found near the foot of hills. Spring water is often used for drinking because as it passes through rock, any harmful substances or germs are filtered out. On more level ground, spring water is found by digging a well to reach the underground water. Small outflows of water can lead to the formation of isolated bogs or marshes. 




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Fresh Water



What is a delta?



As a river reaches the sea its flow becomes slower, forming an area known as a delta. As the water slows the tiny particles of silt carried by the current settle to the bottom, forming mud banks. These make the river-bed shallower, so the water spreads out to form a wide estuary. In large rivers like the Danube, islands form among these exposed mud banks, and the river water trickles through a maze of small waterways. This region, which is rich in plants and other wildlife, forms the river’s delta.



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Uphill flow!



Water always flows down a river, but occasionally the flow is reversed. This happens only in very large rivers, when very high tides overcome the normal river currents. In narrow parts of the river valley the water begins to pile up, and eventually a wave called a tidal bore passes back up the river, sometimes for a great distance. This happens in the Amazon in South America, where there is a bore as high as 4.5 m. A smaller bore travels up the River Severn in England.



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Fresh Water


 



Which is the world’s longest river?



The Nile in Africa and the Amazon in South America are the world’s longest rivers. The Nile is 6,670 km long, and the Amazon is 6,448 km long. It is difficult to give an exact length because these huge rivers split into tiny tributaries near their sources, and some of these dry up or change course.



The Amazon is by far the largest river because it carries more water than the Nile, Mississippi and the Yangtze put together. The Amazon is 140 km wide at its mouth, and up to 91 m deep in places.



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How does a river begin?



Most of the rainwater that falls on the land returns to the sea by way of rivers. Rainwater first soaks into the ground, but once the ground is saturated the excess water begins to run off in small streams. More water comes from melting ice and snow. Small streams gradually merge and become bigger, until they eventually form a river. The tiny streams that are the source of a river often begin in damp areas such as swamps or bogs, or may flow out of a pond or lake. Usually they are in hills or mountains, where the rainfall is heaviest. 



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Oceans



 



 



What causes the tides?



Tides are caused by the gravity of the Moon. As the Earth spins round, the water in the oceans is ‘pulled’ towards the Moon slightly, making a bulge. There is a corresponding bulge on the other side of the Earth. Wherever the bulges are positioned it is high tide. In between the water is shallower and so it is low tide. High tides occur every 25 hours, because at the same time that the Earth is spinning on its axis, the Moon is travelling around the Earth once every 27  days. This means that high tide is about one hour later every day.



 



 



 





 



What is the continental shelf?



The shallow underwater plateaus of land surrounding the continents form the continental shelf. They slope gently down to a depth of about 180 m, after which they slope more sharply towards the deep ocean. The continental shelf can extend out from the coast for long distances, or it may be narrow, for example off the coast of Chile where the Andes Mountains plunge down into the Pacific with hardly any shelf. Usually the shelves are wider off low – flying regions. The continental shelf is a valuable resource, as most fish are found here. Also, there are plans to mine some of the minerals on the sea – bed in these shallow waters.



 



 





How deep are the oceans?



The depth of the oceans varies widely, but the deepest part found so far is called the Marianas Trench. This trench is a deep cut in the bed of the Pacific Ocean, and its depth is as much as 11,034 m. Even at this enormous depth, signs of marine life have been seen in the trench. In 1960 Dr Jacques Piccard and Lt Donald Walsh reached a depth of 10,911 m in a US Navy vessel, Trieste. The Pacific Ocean is home to nine of the ten deepest sea trenches. The exception is the Puerto Rico trench in the western Atlantic Ocean, which has a maximum depth of 9,220 m.



 



 



 





 



Why did sailors fear the Sargasso Sea?



Sailors feared that the Sargasso Sea was haunted by sea monsters and filled with seaweed that would entangle their ships and prevent their escape. The Sargasso Sea is a patch of ocean in the North Atlantic, about 3,200 km west of the Canary Islands. The ocean currents in this area are very slow, although they are surrounded by fast moving currents. This means that any seaweed floating in the Sargasso Sea will not be carried away. Patches of floating weed can be as large as 30 m in diameter. Despite the legends, they are never thick enough to entangle a ship.



 


Oceans



 



Why is the sea salty?



A mixture of salty substances is washed out of rocks by rivers and deposited in the sea. When rain falls on the land it gradually dissolves minerals. The dissolved salts slowly enter rivers and streams, and are carried down eventually into the sea. This process is happening all the time, and so the oceans and seas gradually become more salty.



 



 



 





 



 



 



What is the Gulf Stream?



The Gulf Stream is an ocean current that controls the climate and weather of the whole of Europe. The current starts in the Gulf of Mexico, carrying warm water across the Atlantic and travelling northeast until it reaches the European coast. Water evaporates from the surface of the Gulf Stream causing rainfall in Western Europe.



 



 



 


Continue reading " Oceans"

Day and Night


Why are times different in other countries?



Clocks in other countries need to be adjusted so that it gets light and dark at approximately the same time everywhere. Without this adjustment, people might find that dawn was at 10 o’ clock in the evening, for example.



In 1884 time zones were set up around the world, measured from Greenwich in London, England. Every time zone east or west of Greenwich has noon at a different time. Each zone is either one hour ahead or behind of its neighbouring zone – it is one hour earlier to the west of each zone, and one hour later to the east.



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What are the northern lights?



           The northern lights are streaks and sheets of pale, flickering, coloured lights that are sometimes seen in the night sky in far northern regions. Their proper name is the aurora borealis. The same effect also occurs in the far south, where it is known as the aurora Australis.



            Auroras take place between 97 and 1,000 km above the Earth’s surface. They are caused by electrically charged particles from the Sun. These particles strike the Earth’s atmosphere and release energy in the form of light. Auroras are most common when there are many sunspots, which increase the amount of energy released by the Sun.



Picture credit: google


Day and Night


 



Why do we have coloured sunsets?



Coloured sunsets happen when light is scattered by dust and water particles in the air, as the Sun sets. At sunset, the light passes through a much greater thickness of air, because it strikes the atmosphere at a shallow angle. The farther the light has to pass through the air, the more likely it is to be scattered by the dust particles, causing the red colouration.



 



 



 





 



 



 



Why does the Sun rise in the east?



The direction of the Earth’s rotation means that the Sun appears to rise in the east and set in the west. If you imagine that you are standing at the North Pole and looking down on the Earth, it would rotate anti clockwise. In other words, the Earth rotates towards the east, so the Sun first becomes visible from that direction.



 



 



 





 



 



 



 



What is the Earth’s axis?



The Earth’s axis is an imaginary line through the geographic centre of the Earth about which it spins. You can think of the axis as being like a stick pushed through the middle of an orange. The axis is tilted at an angle of 23.5 degree from the vertical, in relation to the Sun. We still do not know the reason for this tilt.



 


Day and Night



 



Why do we have day and night?



As the Earth spins on its axis, the Sun always shines on one side giving us daylight. It is night on the shaded side. As the Earth continues to turn, the shaded side moves into the Sun’s light and the sunlit side turns away from the light. It takes 24 hours for the Earth to make one complete turn on its axis, and our clocks are based on this principle.



In the 1940s, people discovered that the Earth speeds up and slows down a little as it spins, although the reason for these changes is not fully understood. We have now developed atomic clocks that can measure time exactly.



 



 



 





 



Why do we have seasons?



We have seasons because the Earth is tilted on its axis. As the Earth moves around the Sun, the hemisphere tilted towards the Sun receives more sunlight and this is summer time. The days are longer and the weather is warm because of the extra sunlight. The hemisphere tilted away from the Sun receives less sunshine, has shorter days and is cooler – it is winter time. The area near the Equator is always exposed to the Sun’s rays, so it is warm all the year round. This means that there is little difference between the seasons.


Our Planet Earth



 



What are metals?



Metals are one of the major groups of elements. Most of them are shiny and hard. Mercury is the only metal that is a liquid at normal temperatures. Most metals can be bent and stretched, and they can be mixed to make alloys.



Metals are usually found with other elements in the form of compounds. Bauxite is an ore, or mixture of substances, that contains aluminium, the commonest metal. It makes up about eight percent of the Earth’s crust. Osmium is the heaviest metal, and is twice as heavy as lead. Lithium is the lightest metal. It is half the weight of the sane volume of water, so it floats in water.



 



 



 





 



 



How much of the Earth is covered by water?



More than two-thirds of the Earth’s surface is covered by seas and oceans. About 72 percent of the Earth’s surface is water. This water is either in the oceans, locked away as ice at the poles, or held as water vapour in the atmosphere. All of the Earth’s water is known as the hydrosphere. 



 



 



 



 



 





 



 



 



Why is the Earth round?



Gravity pulled the Earth and the other planets into a sphere when they were being formed. The Earth is not truly round, but is slightly flattened making it bulge out at the Equator. This effect is due to the speed with which the Earth spins, causing the Equator to try to fly out from the axis of the spinning Earth. It is rather like a heavy object whirling round on the end of a piece of string. The shape of some of the other planets is distorted in the same way.


Our Planet Earth


 



 



What is the Earth made of?



The Earth is made up of elements. These are the simplest possible substances, which are composed of one kind of atom. Elements cannot normally be broken down into other substances, except under the special conditions that you might find inside the hot core of a star. A total of 92 different elements are found in nature. Other elements can be made in laboratories, but they have only a very short life.



Minerals, which make up the solid surface of the Earth, consist mostly of combinations of elements. The minerals gold, diamond and graphite are examples of single elements, while most others contain several elements. 



 



 



 



 





 



What are crystals?



Crystals are solid substances that are naturally formed into regular geometric, angular shapes. All crystals can be classified into seven systems. Sometimes a crystal is formed when water evaporates, and substances dissolved in the water gradually grow into a crystal. Other crystals are formed under great pressure. Diamond crystals are made when carbon dissolves in molten rock deep down below the Earth’s surface. The diamond crystallizes out and is later uncovered on the surface either by volcanic action or by erosion of the Earth’s crust. Other valuable gems are formed in a similar way, and most of them contain compounds of aluminium.



 



 



 





 



 



What is the Equator?



The Equator is an imaginary line drawn around the outside of the Earth. It lies midway between the North Pole and the South Pole, at the Earth’s broadest point.



The Equator was invented by map-makers because it makes a convenient point from which to measure distances, together with the geographic North Pole and South Pole. On a map, the Equator is positioned at 0 degrees of latitude. It divides the Earth into two halves, which we call the north and south hemispheres. 


Our Planet Earth



What is inside the Earth?



The Earth is not solid rock all the way through. It has an inner core of solid rock, which is mostly iron. The temperature here is probably around 4,500°C. Beyond the inner core is a layer of liquid rock, called the outer core, which extends about halfway to the surface. Beyond this is a thick layer of rock called the mantle, which is partly molten and runny. The thinnest layer, or crust, is on the Earth’s surface, floating on the red-hot liquid mantle. The crust is about 6 km thick under the oceans, but 30 to 40 km thick beneath the land. 



 



 





 



 



Why is the Earth like a magnet?



The Earth acts as if it is a huge magnet. When the solid rocky core moves inside the liquid rock above it, it creates a magnetic field with a north pole and a south pole. This field surrounds the Earth and extends right out into space. The Earth’s magnetic field is changing constantly. This means that the magnetic north pole is not always the same as the geographic, or true, North Pole that you find on a map, although it wanders about in the same region. Millions of years ago, the north magnetic pole lay in what is now the Sahara desert. 



 



 



 





 



How old is our Earth?



The Earth is thought to be about 4,600 million years old. The oldest rocks so far discovered are up to 3,800 million years old. The Universe is much older, and probably began about 15,000 million years ago. We can calculate the ages of the Earth and the Universe by examining meteorites, and also by looking at changes in the atomic structure of some of the elements found on the Earth. Radioactive elements decay at a steady rate, and these changes can indicate the age of the Earth and other planets, as well as the age of the stars. 


Space Travel



 



 



 



Has any spacecraft ever left the Solar System?



Pioneer 10 is the first man-made object to leave the Solar System. This probe was launched towards Jupiter in 1972 and by 1983 it had reached deep space. Pioneer 10 carried messages about life on Earth to be read by any extraterrestrial travellers who might meet the probe. 



 



 





 



 



What is a space station?



Space stations allow the crew to work in space for long periods in conditions of zero gravity. While conditions in space capsules and the space shuttle are cramped, space stations are more suitable for longer stays in space. Rockets or the space shuttle bring supplies of air and food to the space station, and often a new crew. Space stations are usually made up of several modules that are sent into orbit, one at a time, and assembled in space. Some space stations, such as the Russian Mir, stayed up for many years, and their crews remained in space for months at a time. 



 


Continue reading "Space Travel "

Space Travel


 



 



Rocker power!



All space flight depends on the use of rockets that burn huge amounts of fuel. They burn high-energy fuel in a chamber which directs the burning gases through a nozzle. As the gases stream out through the nozzle they provide the thrust to push the rocket up into space.



Some rockets are powered by burning kerosene or liquid hydrogen with liquid oxygen, but this requires very careful handling. Other rockets burn solid fuel in a controlled explosion.



 



 





 



One giant leap!



The Apollo project was the United States’ plan to get humans on the Moon during the 1960s. It used the world’s most powerful rocket, Saturn V, to launch the three-man Apollo spacecraft. While orbiting the Moon, the Apollo craft would separate into two parts. The landing module carried two astronauts down onto the Moon’s surface, while the main part remained in orbit with the third astronaut. 



 



 



 



 





 



 



How do satellites stay up?



The speed with which a satellite is launched helps to keep it in orbit. To stay up above the Earth, a satellite must be launched at a speed of about 8 km per second. If the orbit is less than 200 km above the Earth, faint traces of air will gradually slow the satellite so it loses height and eventually crashes to the ground. Satellites that are much higher can stay up indefinitely. Some satellites are placed in a geostationary orbit. This means that their speed exactly matches that of the Earth’s rotation, and they seem to stay above a fixed point on the ground.