My Science School

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.

Fact File: Mountains such as the Rockies in South America, do not see a dramatic movement in the snow line. This is because they are so high up. The climate is very cold in winter and the summers are short-lived.

 

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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.

Fact File: Eskimos live in houses made completely of snow called igloos. The Eskimos cut away blocks of snow and build the igloo as though they are bricks. Because where they are built is so cold, the igloos do not melt.

 

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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.

Fact File: Rainforests have developed in areas where the soil is very fertile and where there is a great deal of rainfall. The varied vegetation suggests the soil is extremely nutrient-rich.

 

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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.

Fact File: Soil is not just a single, consistent layer of material.

 

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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.

Fact File: When rivers reach land close to sea level, they begin to meander, forming a snake-like shape on the land. This is caused by the gradual dropping of the sediment it carries where the flow is weak.

 

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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.

Fact File: Too much rainwater can have disastrous effects on the land. Flooding washes away fertile soil, and begins eroding the land.

 

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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.

Fact File: Some people believe that animals are good predictors of weather. One such belief is that if cows are standing in their field, then dry weather is expected. If they are lying down, however, rain is expected.

 

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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.

Fact File: Lighthouses were built to worn ships at sea that they were approaching land and rocky water. Their beam of light across the waves made travelling by boat much safer.

 

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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.

Fact File: Some living things have adapted to survive long periods of time without water. Plants such as cacti have the ability to conserve water. They also minimize water loss as they have no leaves, and photosynthesis takes place in the stem. They have roots which reach deep into the ground for water.

 

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The Sun is our nearest star. Stars are massive reactors generating energy in their cores. It is the heat and light from the Sun that makes life on earth possible. The Sun for us is a pretty steady and dependable thing. Whether we can see it or not, we know it is always there, and the answer to this question is – the Sun NEVER stops shining.

As the Earth spins on its axis, the Sun always shines on one side giving us daylight. Another time when the sun is not visible is during a solar eclipse. This is when the Moon blocks the Sun’s light from the Earth, so that the Sun seems to disappear.

Fact File: The direction of the Earth’s rotation means that the Sun appears to rise in the east and set in the west. The Earth rotates towards the east, so the Sun first becomes visible from that direction.

 

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About one-third of the world’s land surface is covered by desert. Not all these deserts are hot and arid.

Antarctica is the biggest cold desert in the world. The blanket of two-km-thick ice covering the Tundra, howling winds and freezing temperatures stop plants and land-living animals from surviving. But the ocean around this frozen desert is full of fish and krill, so the coasts are home to millions of birds. Once the Antarctic winter sun sets, it is dark for more than two months.

The Gobi desert in Mongolia and western China is also very cold in the winter, when temperatures drop below freezing. However, the temperature in the summer is hot.

Fact File: One of the animals that has survived the Arctic conditions is the polar bear. In very cold climates, animals need excellent insulation to stop their body heat from escaping. This can be in the form of dense hair, fur or feathers, or on the inside, in the form of a thick layer of fat or blubber.

 

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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.

Fact File: About one-third of the world’s land surface is covered by desert. Deserts are found wherever there is too little water to allow much plant life to grow. Salt deserts form when shallow seas and lakes dry up, leaving a deposit of smooth salt.

 

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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.

Fact File: There is an old saying regarding the weather: if the oak tree has its leaves before the ash then it will be a fine summer.

 

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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.

Fact File: The higher we go the less air pressure there is. This is the reason that space suits and the cabins of high-flying planes are pressurized. They are designed to maintain the air pressure our bodies must have.

 

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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.

Fact File: Fog particles are small, less than 1/25,000 of an inch in diameter. When you have a dense fog and can’t see in front of you, it is because there may be as many as 20,000 of these particles in one cubic inch.

 

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