Category Our World

We know the Mediterranean today as a huge sea off the coast of Europe. However, the Mediterranean was not always like that. Approximately 5 million years ago, the Mediterranean was a dry basin. Movements in the Earth’s crust opened up the Gibraltar Straits between the continental areas which are now Africa and Europe. The Atlantic Ocean would have poured through this new opening into the dry basin. The result would have been an enormous waterfall, nearly 800 metres high. So much water poured in from the Atlantic that the Mediterranean Sea was created in only a few years.

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No one knows for certain when the Earth was formed exactly. However, scientists have reasoned that it probably formed about 6,000 million years ago.

The most scientific reasoning for the creation of Earth is that it began as a huge ball of hot gases which cooled to form the planet. Seas of dissolved chemicals would have covered the land, and the air would have been an atmosphere of different gases. The atmosphere was thought to have consisted of swirling gaseous clouds which most likely caused huge electrical storms.

The poisonous gases in the atmosphere must have reacted to produce oxygen, which triggered off the first beginnings of life on Earth.

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Snow lines are clearly visible on mountains. They mark out the area above which a mountain is permanently covered in snow.

The highest points of a mountain are much colder than the lower points. The snow which falls on the higher regions never thaws because it is so cold. In the summer, however, the warmer weather begins to melt some of the snow. This causes the snow line to move up the mountain.

As the summer months pass by and the winter months return, the snow line moves further down the mountain once again.

In colder regions, the snow line is close to ground level, but where the air is warmer, the snow line is closer to the Equator.

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Water turns into snow at temperature above -40 . Snow forms when water in clouds freezes into tiny ice crystals. This moist air freezes around minute dust particles or chemical substances floating in the clouds. These particles become the core, or the nucleus, of each crystal. Snow crystals grow in size when more water crystallizes around a particular nucleus. This happens more if the air is humid.

Snowflakes are formed when a number of crystals join together in clusters. The structure of snowflakes is often a beautiful, hexagonal form. It is believed that no two snowflakes can be identical. These fall from the clouds onto land as snow.

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When vegetation first starts growing in newly formed soil, it is disadvantage because the soil will not be nutrient-rich. As the plants die, they enrich the soil, allowing more plants to take advantage of this. As the soil gets older, it has gleaned more and more nutrients from dead plants – and more and more plants are able to grow successfully in the soil. Climax vegetation occurs when the vegetation is totally suited to soil. In reality, this can never last permanently due to the ever-changing environment.

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Soil changes its appearance when the biological or chemical make-up of it varies. For example, red soil is found in areas where there is a high content of iron compounds. Oxisol is a good example of this; it is found in tropical regions where both chemical and biological activities are high.

If you thought that all soils are brown, think again. Soil colours range from black to red to white. Sometimes it can even be blue! Soil colour mostly comes from organic matter and iron. Topsoil is often dark because of organic matter. An even, single colour indicates the soil is well drained. In contrast, rusty spots and grey patches (sometimes even a light blue in colour) indicate poor drainage.

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There are two main ways in which rivers begin. Some rivers start when a natural spring releases water from underground. These are often small trickles of water which develop into small streams. In turn these streams increase in size until they are acknowledged as rivers.

Other rivers begin when persistent rain makes a groove or a channel in a piece of land. As more and more rain falls into this channel, a flow of water slowly begins. Just like the springs, a stream can soon develop into a river.

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Water cycles demonstrate how water evaporates from the oceans then rises in the air to form clouds. In areas of low pressure, the clouds release the water as rain. This falls into the oceans again, or falls onto the land where it gradually works its way back into the oceans via streams and rivers. This is a continual, cyclical process.

However, in some areas of the world where there is no rainfall for long periods of time, local water cycles do stop. When one event in the cycle fails to happen, the cycle breaks down.

But water can neither be created nor destroyed – it will always exist in some form. If you consider the world as a whole, with one big water cycle, the processes involved are always occurring somewhere: this cycle never stops.

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The longest drought in recorded history took place in Calama, in the Atacama desert of Northern Chile.  For four centuries, beginning in 1571, no rain fell in the area. It was not until 1971 that rainfall was first recorded again. The Atacama desert, which lies between the Andes and the Pacific ocean, is recognized as the driest place in the world.

The Atacama desert remains so dry because it lies in a region where there is constant high air pressure, with little air movement, and with few clouds overhead.

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Water becomes salty when minerals (including salts) dissolve into it. This process begins when rainwater falls on the land and erodes rock. The minerals found in rock are dissolved into the rainwater.

These dissolved minerals in the rainwater enter streams and rivers, gradually working their way into the seas and oceans.

This is a process which is constantly taking place, so the level and concentration of salt in the oceans and seas is always increasing. Some of the minerals are consumed by organisms in the water, but the vast majority of them make up the saltiness of the water.

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The longest heatwave ever recorded was in Marble Bar, Australia when the temperature stayed above 38 . It lasted for 162 days from 23 October 1923 to 7 April 1924.

The highest average annual temperature recorded is 34.4  in Dallol, Ethiopia.

The lowest recorded temperature (outside of the poles) was -68  in Verkhoyansk, Siberia, on 6 February 1933.

The lowest average annual temperature of -56.6  was recorded at the Plateau Station, Antarctica.

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Mirages form in hot deserts where the air is so hot it bends and distorts light rays. The shimmering images that a mirage produces have often tricked travellers in deserts. People think that they can see an oasis or town on the horizon, but in reality it is not there.

Under certain conditions, such as a stretch of pavement or desert air heated by intense sunshine, the air rapidly cools with elevation and therefore increases in density and refractive power. Sunlight reflected downward from the top of an object. When the sky is the object of the mirage, the land is mistaken for a lake or sheet of water.

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People have been able to forecast the weather for hundreds of years. Meteorologists have used simple instruments like thermometers, rain gauges, barometers and wind gauges for many years, but with the arrival of satellite photography, weather forecasting has been transformed. With the use of computers, increasingly accurate forecasting is now possible.

Traditional forecasters have been known to use pine cones, which open and close according to the humidity of the air. An open cone is supposed to mean dry weather. Seaweed also responds to changes in humidity. Dry seaweed indicates dry weather.

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A barometer is used to measure the changes in air pressure. Air pressure varies across different parts of the Earth’s surface, and these differences cause winds. Air moves from an area of high pressure, or an anticyclone, to an area of low pressure, or a depression. Depressions are usually associated with worsening weather conditions and rain. In a mercury barometer the air pressure pushes down on the mercury, which is forced up the barometer to give an accurate reading.

Air pressure is greatest at sea level, where it amounts to 14.7 pounds a square inch. It is greatest there because that is the bottom of the atmosphere. At highest altitudes the pressure is less.

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It is tiny water droplets condensing from moist air that cause fog and mist to rise. The water droplets can occur at ground level. The air can only hold a limited amount of water. If the air suddenly cools, its capacity to hold water is reduced, which results in a mist or fog.

When fog develops, visibility can be affected quite badly. Mist is less dense. It often occurs on calm, clear nights when heat rises, forming a thin layer of mist close to the ground. Mist often forms over water because a mass of warm air passes over a cold stretch of water.

Sometimes visibility is affected in built up areas due to mist and fog, but this is sometimes mistaken for smog. Smog is a buildup of exhaust fumes and factory smoke which hangs over the area until a huge amount of air movement can blow the smog away.

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A monsoon is a season of very heavy rain falling is tropical countries. Monsoons are most common near the Equator. They occur when seasonal winds spring up carrying moist air in from the sea. Important crops such as rice depend entirely on the monsoon season to provide the right growing conditions.

If the monsoon rains fail, famine often follows. There are also some special winds called monsoon winds. These are winds that change their direction with the season. In India, the monsoons blow south as hot, dry winds in the wintertime, and blow north in the summer, bringing heavy rainfall.

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Mount Everest, which is in the Himalayas, is 8,863 metres high. At these altitudes, mountains are always covered in snow and ice, and there is little oxygen to breathe. Mount Everest was finally conquered on May 29, 1953, when a Nepalese guide, Tenzing Norgay, and a New Zealander, Edmund Hillary, reached the highest point on the Earth’s surface. Since then, many people have climbed Everest, and all the world’s major peaks have now been conquered.

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Mountains can be formed in three different ways. Volcanoes form mountains when lava from deep inside the Earth cools and hardens on the surface.

Other mountains are formed when two plates move towards each other under pressure or where an oceanic plate is pushed under a continental crust. The pressure causes the ground near the joining plate margins to fault and fold. The ground is forced upwards to form mountains. The Rockies, Alps, Andes, Urals and Himalayas were all formed in this way.

Finally the Earth’s crust can fracture and create faults which mean that large blocks of land can be moved upwards or downwards. Faults in the rocks normally occur when there is a lot of pressure on the rocks. Mountain building is a slow process and happens over centuries.

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The island of Krakatau, Indonesia (west of Java) was a small volcanic island. The volcano itself had laid dormant for over 200 years until August 1883. On May 20 one of the cones erupted violently and three months later the whole island blew up. It was the biggest explosion in recorded history. For two and a half days the island was in total darkness because of the amount of dust in the air. A cloud of ash rose 80 km into the air. The eruption caused a tidal wave which killed 36,000 people. The explosion could be heard and felt in Australia, 3,500 km away.

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The word dormant actually means ‘sleeping’. So when people talk about a volcano being dormant, it really means it is temporarily sleeping and might erupt at any time in the future. An extinct volcano, on the other hand, is one that will not become active again. Like earthquakes, volcanoes mainly occur along fault lines. Earth’s crust to release the pressure that has built up. When there is very little pressure the volcano can remain in a dormant state for many, many years. On the island of Maui there is a volcano called Haleakala which rises to a height of about 10,025 feet. It is the world’s largest inactive volcano. Its crater is about 20 miles around and some 2,720 feet deep.

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Sometimes there is a big news story about an earthquake that happened in some distant part of the world. Although people living in that area didn’t feel the earth shake, scientists probably made a complete and exact have special instruments called seismology. The seismograph picks up the one rock mass rubbing against the other. The energy of this rubbing is changed to vibration in the rocks. This vibration can travel many thousands of miles.

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Our planet is a very restless place. Every 30 seconds, the ground suddenly rumbles and trembles. Most of the movements are so slight that they are not felt. Others can be so large they cause complete disaster. Big cracks appear in the land, streets buckle and buildings simply crumble. In fact whole towns and cities can be destroyed. These are called earthquakes and the reason they occur is because the Earth’s crust is made up of moving parts called plates. When these plates slide past or into each other, the rocks jolt and send our shock waves.

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In the former Soviet Union the direction of several rivers was diverted or even reversed to provide water for irrigation. Some of the rivers running into the Aral Sea were diverted northwards in a huge water management project to irrigate land north of the region. In some cases the direction of their flow was reversed. The result was that the Aral Sea began to dry up because no more river water flowed into it.

Sometimes the flow is reversed naturally, but this only happens 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.

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

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Some sort of force or energy is needed to start a wave, and it is the wind that provides this energy in the water. Wind blows the surface layers of the sea, gradually a rolling movement of waves. As these waves near the coast, the sea-bed interrupts their rolling movement and they mount up and break onto the beach. The water inside a wave moves round and round in a circle. Near the shore, the circular shape of the wave is changed and it becomes squashed. The top of the wave becomes unstable, so when it hits the beach, it topples and spills over. On beaches with a shallow slope the waves pile up to a great height before breaking, causing surf.

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In Antarctica and the Arctic, the oceans freeze because the temperatures are so low. Seawater, unlike fresh water, continues to increase in density as its temperature decreases towards freezing point (about -1.8 ). In fact Antarctica contains 90 per cent of all the ice on the Earth. Scientists have calculated that should all this ice melt, sea levels would rise by 60 m causing world-wide flooding. An accumulation of sea ice can cause an iceberg which floats in the sea because it is less dense than water.

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 The Moon is 400 times smaller than the Sun but about 400 times closer. So we see them both as about the same size.

A solar eclipse is when the Moon blocks out the light from the Sun. This can make the day turn dark as all the light from the Sun is blocked out in a total part of the light is blocked out.

The Sun is our nearest star. It is 149.6 million km (92.9 million miles) away from Earth. It is the heat and light from the Sun that makes life on earth possible. The huge gravity pull of the Sun keeps the planets of our solar system orbiting around it.

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The Earth casts a long shadow into space, and when this shadow passes over the Moon it can cause an eclipse.

A lunar eclipse can only happen during a full Moon, when the Sun is directly behind the Earth. It happens only occasionally, because the orbit of the Moon is slightly tilted and so the shadow usually misses it. Lunar eclipses can last for over one hour, but they do not completely black out the shadowed part of the Moon. Some sunlight always filters through, making the shadow look a reddish-brown colour. Eclipses can only be seen from certain parts of the world.

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The shortest day of the year is in the winter solstice which is 21 December. When the Northern Hemisphere is turned toward the Sun, the countries north of the equator have their summer season, and the countries south of the equator have their winter season. When the direct rays of the Sun fall on the southern hemisphere, it is their summer and it is winter in the northern hemisphere. There are two days in the year when night and day are equal all over the world. They come in the spring and fall, just halfway between the two solstices. One is the autumnal equinox in September, and the other is the spring equinox in March.

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The earth revolves around the Sun and at the same time it revolves on its own axis. As it moves around the Sun, it is also spinning like a top. If the axis of the earth were at right angles to the path of the Earth around the sun, all the days of the year would be the same length. However, the earth is tilted at an angle of 66.5 . In June the northern hemisphere is tilted towards the Sun and it receives more sunshine during a day. This is its warmest season called summer. On the 21 June the Sun is directly over the Tropic of Cancer and it is midsummer in the Northern hemisphere. This is the time known as the summer solstice.

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