Category Geography

MORE ABOUT CLOUDS

 

 

 

The fluffy, white clouds you see on fine, summer days are called ‘cumulus’ clouds. When these rise up to form dark ‘cumulo-nimbus’ thunderclouds, there is a good chance of a heavy shower or a thunderstorm.

‘Cirrus’ clouds are the thin, wispy clouds you sometimes see very high in the sky on dry days. They usually mean a front is arriving, so you can expect the weather to change. As a front moves nearer, the cloud gets lower, turning into ‘alto-stratus’ or small ‘alto-cumulus’. Tall heaps of alto-cumulus means there may be a storm. Lower down, grey ‘nimbo-stratus’ clouds often cause continuous rain. ‘Stratus’ clouds form as a low sheet and often cause fog.

INTRODUCTION – PLANET EARTH

Planet Earth is our home. It is also home to millions of different plants and animals. Like the human race, the planet Earth has a history – only many millions of years longer.

 

 

 

 

The Utah desert in the United States. Deserts cover a fifth of the Earth’s surface.

 

 

 

 

Have you ever wondered what makes the light and dark of the day and night? Or what causes leaves to fall from trees, the sun to rise, or the tides to change? Find out how the movement of our planet around the Sun causes different patterns for life on Earth, and how the Earth’s climate has evolved throughout the planet’s history.

 

 

 

 

The Earth’s oceans are home to many different species of wildlife.

PLANET EARTH

 

When you look out to sea, the horizon (or skyline) seems curved. This is because our planet is shaped like a ball; it measures about 13,000 km across. The land and water that you see are only a small part of the Earth’s surface. Seen from space, Earth is almost perfectly round and appears to have a smooth surface. The highest mountain is 9 km high, and the deepest ocean is about 11 km deep. These distances are very small compared to the size of the Earth.

 

The Earth is one of many planets in our solar system. But it is the only planet which has the right conditions for human life. Other planets are too cold or too hot for us to live there, or their atmospheres are too poisonous.

Our planet Earth is made up of the atmosphere the land and the oceans.

 

THE EARTH’S ORIGIN

 

The Earth began over 4,600 million years ago. We believe that the Earth and other planets were formed from a flat gas cloud around the Sun. This cloud formed into small, cold particles which attracted one another, collided, and formed larger particles. This took place over a few million years. As the larger particles collided, they became hot, and melted. Iron from these formed the central core of the Earth, and other substances surrounded it.

The molten outer layer of the Earth cooled to form a thin shell. Sometimes molten rock escaped from under the surface in volcanic eruptions, as it still does today. Gases escaped from inside the Earth to form an ‘atmosphere’.

 

 

 

 

Structure of the Earth

The outer layer of the Earth is a thin, solid skin, called the ‘crust’. Below it is a region called the ‘mantle’? The outer layer of the mantle is made of molten rock, called ‘magma’. Below the mantle is a region of molten rock under great pressure. The central region of the Earth is a solid core.

Scientists predict that the temperature in the Earth’s core is about  6,000 degree C. They have studied temperature changes at different depths beneath the Earth’s surface and also believe that the melting point of iron – found near the Earth’s central core – is a good indication.

 

 

Continue reading “THE EARTH’S ORIGIN”

CHANGING EARTH

The remains of ancient animals, or ‘fossils’, tell us that our planet and the life on it were once very different from today. Throughout the ages, the Earth and its climate have changed, sometimes dramatically – like the coming of the ice ages. The most recent ice age began 70,000 years ago, and lasted for 60,000 years.

 

 

 

Plants and animals living on Earth have adapted to changes in the planet, to improve their chances of survival. Sometimes plants and animals have also caused changes to the Earth. For example, the soil in your garden was partly formed from the rotting remains of dead plants and animals, called ‘humus’.

 

 

 

 

 

 

 

 

During the ice age, the Earth’s land was mainly covered with snow and ice.

 

 

 

 

 

The Earth in a day

Imagine the changes of the Earth’s lifetime squashed to fit into a 24-hour day. On this scale, there would be no life on Earth until about 6.30am, when the first microscopic plants and animals would appear. Large animals with backbones, like fish, would not appear until about 9.15pm. The first plants would appear about 9.45pm and some fish would take to the land at 10.00pm. Reptiles would appear at about 10.30pm. Dinosaurs and early mammals would be living on Earth about 11 pm, but mammals would only become common about 11.40pm. People would appear on Earth 40 seconds before midnight and the first written history would be documented about ten seconds before midnight.

MOVING CONTINENTS

The Earth’s crust is relatively thin, and is formed of large, flat pieces, called ‘plates’. Each crustal plate may be thousands of kilometres across. These plates are moved very slowly by movements of the magma underneath. Where two plates push against each other, the crust crumples to form mountains. Where they move apart, magma can escape to form new rocks. Originally the Earth’s land was close together, but over time the crustal plates have moved the land apart.

 

 

 

 

Changing times

200 million years ago the main land masses that we know today were all grouped close together (1). Over many millions of years, crustal plates carrying the continents have moved away from one another (2). 65 million years ago the continents had moved even further apart (3). Today the continents are still moving a few centimeters each year (4). The coastlines are also being slowly eroded by the sea. How will the continents look in 100 million years time?

 

 

 

 

When crustal plates press against each other, they do not slide smoothly. Instead, they press and press until suddenly they break at a weak point. As they break, there is a sudden movement of the crust, which we feel as an earthquake.

Occasionally, some of the mantle can push through weak points in the crust, and form a volcano. The crust is usually weaker along or near the lines where plates meet.

Earthquakes can cause a great deal of destruction.

 

 

 

 

 

The Sierra Nevada Mountains, USA, were formed by two crustal plates pushing against each other.