Category Social Sciences

SPINNING EARTH

 

 

 

The Sun appears to us as if moves around the Earth. In fact, the Earth spins around on its axis like a top, one turn every day. The place where you live, points towards the Sun in the day, and away from it at night.

The Earth spins on its axis at a great speed: the surface of the Earth moves at more than 1,500 km/h. Gravity provides the force which stops us being thrown off the Earth. Gravity extends a long way from the Earth, and pulls anything within its range towards the Earth. The Moon and artificial satellites are held in orbit round the Earth by the pull of its gravity.

 

 

 

 

The seasons

The seasons are caused by the Earth’s orbit around the Sun. The diagram shows how the Earth’s axis is slanted. During summer in the northern world, the midday Sun is over a region north of the equator, so its rays are more concentrated and feel hotter. During winter, the Sun is over a region south of the equator, and the rays reaching the north spread out over a larger area. They are less concentrated, so they feel less hot. Places south of the equator have their summer when places north of the equator have winter.

 

 

 

 

 

Continue reading “SPINNING EARTH”

CLIMATE

Different parts of the globe have very different climates. It gets hotter as you travel towards the equator because the Sun’s rays are more concentrated there. Places near the sea are usually cooler in summer and warmer in winter, than places inland. This is because the sea heats up and cools down less easily than the land, and so keeps the land near the sea warm in winter and cool in summer.

These differences in temperature cause movements of air across the Earth’s surface, called winds. Air movements, in turn, cause clouds and rain to form, as warm, moist air is cooled by rising up over hills.

 

 

 

The Sun’s rays travel about 150 million km to reach the Earth, providing our planet with light and heat. By rotating once every 24 hours, the Earth keeps the distribution of heat and light balanced with regular alternating periods of daylight and darkness.

The Sun’s rays fall at both the equator and the poles. At the equator, the Sun’s rays are spread over a smaller area than rays reaching the Earth at the poles. This means that sunlight reaching Polar Regions is less intense than sunlight reaching the equator. It also means that places near the poles are colder than places near the equator.

 

 

 

 

 

Temperatures drop considerably at the two poles, which are mainly covered in snow and ice.

 

 

 

 

 

 

 

The hottest and driest climates on Earth are found in the deserts.

 

 

THE ATMOSPHERE

 

 

 

 

The air you breathe forms a thin layer – the ‘atmosphere’ – around the Earth. This stretches up for a few hundred kilometres. As you go higher, there is less air. At the height where planes fly, there is too little air to breathe.

Most plants and animals need atmospheric gases in order to live. Animals rely on ‘oxygen’ to breathe and plants rely on ‘carbon dioxide’ to make their food. The air also contains nitrogen, small amounts of other gases, and some water vapour and dust. The ‘stratosphere’ and ‘ionosphere’ contain small amounts of ‘ozone’, which is a form of oxygen. A layer of ozone prevents harmful ultraviolet rays from the Sun reaching the Earth’s surface.

 

 

 

 

 

 

 

The aurora is caused by charged particles from the Sun hitting the atmosphere.

 

 

 

 

 

 

 

Exosphere

The highest, outer region of the Earth’s atmosphere is called the ‘exosphere’. Here, conditions are not very different from outer space as there is only very little air indeed.

Ionosphere

The ‘ionosphere’ is made up of electrically charged particles produced when radiation from the Sun hits the upper atmosphere. Near the poles, this causes a brilliant display of lights, the ‘aurora’.

Man-made pollution is now causing a hole to appear in the ozone layer.

Stratosphere

The ‘stratosphere’ extends up to about 80 km above Earth. As you travel upwards in this layer, the temperature rises slightly; nevertheless temperatures are below freezing point.

Troposphere

The ‘troposphere’ contains the air we breathe. Clouds rain and snow all form in this layer. As you travel up through the troposphere, it becomes colder.

EARTH’S BALANCE

The parts of the world affecting our lives are called the ‘environment’. This includes the Earth’s crust, oceans, atmosphere, plants and animals. If the balance between things added and things taken away from the environment is upset, the environment will change.

Many of the things we take from the Earth, like metals and fossil fuels, take millions of years to be replaced naturally. Other things, like wood from trees, are replaced more quickly, but if we use them too fast, they will disappear. Some things we produce, like poisons and waste, are not removed as quickly as we add them to the environment, so they build up as pollution.

Household waste is a serious pollution threat – the UK produces 27 million tonnes each year.

 

 

 

 

Cutting down huge forests can cause changes in the Earth’s atmosphere.

 

 

 

 

 

 

Pollution from industry can also disturb the Earth’s balance.

MORE ABOUT PLANET EARTH

Moving Crust

As the plates of the Earth’s surface move towards each other, one plate may rise over the other one. The one which goes up forms mountains and the one which goes down is slowly melted below the Earth’s surface. Where two plates move away from each other, magma is free to escape. It solidifies to form rock, and a ‘mid ocean ridge’ or a ‘volcanic island’ is formed.

 

 

 

Folding

Movements in the Earth’s plates can also cause the Earth’s surface to buckle and split. Where the surface splits and slips, a ‘fault’ is produced. Where the surface buckles, a ‘fold’ is formed. Many familiar features of the landscape are caused by folds and faults, and these can often be seen in layers of rocks at seaside cliffs. The diagram shows some of the features that can be produced in these ways.

 

EXPLORING THE SOLAR SYSTEM

Watching the Solar System from the Earth is one way of finding out about it. To learn more, people have used rockets to travel into space. There they have been able to look at parts of the Solar System more clearly. But although the first men landed on the Moon in 1969, no one has visited any of the planets. They are too far away and conditions are dangerous for humans.

However, as you have seen space probes – robot controlled unmanned spacecraft – have been sent far into the Solar System. The space probe Voyager 2 has travelled through the Solar System and is now well beyond the orbit of Pluto. As it travels it takes pictures and sends them back to Earth.

 

 

 

Voyager 2

This space probe gas already travelled across millions of kilometres of space, and has collected information on Jupiter, Saturn, Uranus and Neptune. The craft’s onboard computers are reprogrammed during its flight by electronic signals from Earth. The entire vehicle weighs only 815 kilograms. It carries equipment for 11 scientific experiments which are powered by a nuclear generator.

 

 

 

 

 

This is a photograph of the surface of Mars. The surface of Mars – you can see the solar panels of the lander at the bottom of the photo.