Category Geography

ROCKS AND EROSION

 

Rocks are not as permanent as they seem. Rain, wind and freezing weather can cause them to break up over a period of time, into tiny pieces which are washed away by rain and rivers. This process is called ‘erosion’. Where rivers slow down or meet the sea, the rock fragments are left behind forming ‘sediment’, such as sand or mud. Layers of sediment gradually thicken and the tiny pieces of rock become stuck together to form larger rocks. These are called ‘sedimentary’ rocks.

Erosion and sedimentation are slow processes. They may take thousands of years to have a noticeable effect on the landscape about us.

 

 

 

Sedimentary rocks

‘Sedimentary’ rocks are made of layers of small particles. For example, chalk cliffs are made from layers of very small shells and skeletons of sea animals.

 

 

 

 

Metamorphic rocks

Sedimentary rocks are changed when they are subjected to heat and pressure near a volcano. This is how ‘metamorphic’ rocks, like marble are formed.

 

 

 

 

Igneous rocks

‘Igneous’ rocks are formed from magma which has cooled, either slowly inside the Earth, or quickly on the surface. Pumice or pummy stone and granite are formed like this.

 

 

 

 

The Delicate Arch, Utah, USA. Rock shapes like these are formed by erosion.

RICHES OF THE EARTH

All the metals we use are taken from the Earth. Most of them are found in rocks, combined with other substances, while some, like gold and copper are found as pure metal. Many of the ‘fossil fuels’ we use, like coal, gas and oil, are also taken from the Earth. Coal is usually dug out of the ground while gas and oil are extracted by drilling deep holes in the Earth.

Rocks in the Earth’s crust can often be used for specialized jobs. For example, one rock called ‘mica’ is found in thin transparent sheets. It can be used to make windows for high-temperatures ovens, where glass would melt.

 

 

How coal was formed

Coal has formed over millions of years from the remains of ancient forests growing on swamps.

As forest trees and plants died, they fell into the swamps forming layers of dead vegetation. Later, sedimentary rocks formed on top of these layers.

The pressure caused by the rocks made the layers of vegetation denser and harder and formed them into a solid rock – coal.

 

 

 

 

 

Coal is a fossil fuel often mined from underground.

EARTH’S OCEANS

The oceans cover about two-thirds of the Earth’s surface and have existed for more than 3,000 million years!

The top layer of the ocean has a rich plant and animal life, the ‘plankton’. Millions of these minute organisms produce food for all the other sea animals. Plankton is one of the oldest forms of life on Earth. Deeper down at about a hundred metres, it is too dark for plants to grow, so the ocean bottom is mostly bare.

Winds blowing across the ocean cause waves. When winds blow over a great distance across the sea, they build waves which may be many metres tall.

 

 

 

The tides

Tides are caused by the pull of the Moon and the Sun on the waters of the Earth. When both the Sun and the Moon are in line with the Earth, their pulls add up, and the tides are very large. These are called ‘spring tides’. When the Sun and Moon are out of line with the Earth, their pulls oppose each other, and the tides are not so large. These are called ‘neap tides’.

 

 

 

 

Cannon Beach, Oregon, USA. The action of the waves can cause erosion of the coastline.

 

 

 

 

 

Papua New Guinea islands, Pacific Ocean – the seas make up two thirds of the Earth’s surface.

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.