My Science School

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.

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.

 

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.

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.

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 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.

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.

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.

 

 

 

Our world is home to many millions of living things. From the hot, dry deserts to the frozen Polar Regions, at the depths of the oceans, and even inside the bodies of other creatures! All living things are specially adapted to enable them to survive in their different environments.

Living things may look very different, but they all share some basic characteristic: they need oxygen and ‘nutrients’ for nourishment; they move and grow; they get rid of waste substances; they react to things around them; and they can also reproduce.

 

 

 

 

 

Polar bears are specially adapted to live in the cold extremes of the Polar Regions.

 

 

 

 

 

 

 

Chameleons change the colour and pattern of their skin, to blend in with their surroundings and protect themselves from attack.

 

 

 

 

 

 

 

Lions are camouflaged in the hot, dry plains of Africa.

Imagine you were looking at a waxwork model of a child. They model might confuse you at first. It may look very realistic and even share many of the physical features of a child. But you would soon be able to tell that the waxwork was not a living thing.

A real child can move. A child needs to eat and breathe to survive, and gets rid of waste materials, like faeces and urine, from its body. A child can see and hear things happening nearby and will act accordingly. Eventually the child will grow and may even have children of its own. The waxwork model may appear to be very lifelike but it can do none of these things.

Living things can move about, sometimes very quickly, like these human sprinters.

 

 

 

Living things need nutrients for nourishment. This hummingbird is feeding on flower nectar, a good source of sugar. In turn, the flower has been feeding on sunlight and nutrients from the soil.

 

 

 

 

 

 

 

 

We plant many kinds of trees, shrubs and flowers in public places and in our gardens.

There are about two million different types of living things today! Although they share similar features, there are also great differences between them. People have found it useful to sort living things into groups. The two largest groups are the plant and the animal kingdoms.

 

Within these groups there are many different types, or ‘species’. So scientists divide the plant and animal kingdoms into smaller groups. Animals are firstly divided into those that have backbones, the ‘vertebrates’, and those that do not, the ‘invertebrates’. Plants have also been divided into many different groups that distinguish between their structure and their leaf or flowering cycles.

 

The animal kingdom

Most animals are invertebrates (without a backbone). For example, earthworms, butterflies, spiders and crabs are just a few invertebrates. Vertebrates can be put into five groups: fish, amphibians (vertebrates which spend part of their lives in water and part on land), birds, reptiles and mammals. Mammals are the only animals which produce milk to feed their young.

 

Continue reading "THE VARIETY OF LIFE"

Where did all the different types of living things come from? Nobody knows for certain, but many scientists think that plants and animals have gradually developed, or ‘evolved’, over millions of years. As they have changed, they have become better adapted to survive.

For example, millions of years ago plants had no flowers. They relied solely on the wind and the rain to transport their pollen to other plants, so that new seeds could develop. But over time, plants developed simple flowers to attract insects. Insects accidently pick up sticky pollen as they feed on flower nectar, and carry it to nearby plants, helping the flowers to reproduce.

 

 

Human beings may have evolved from ape-like animals. These developed the ability to stand upright on just two feet, so that they could then use their hands for other things. Over millions of years they learnt how to use tools and developed these to become successful hunters.

 

 

 

 

 

 

Fossils are the remains of plants and animals that have been preserved in rock. They give us clues about the life of ancient living things. Scientists can work out the age of fossils by dating the rocks in which they are found.

 

 

 

 

 

Insect-pollinated plants tend to have fragrant, brightly coloured flowers to attract insects.

All living things are made up of tiny building blocks called ‘cells’. Cells are too small to see without a microscope. Some living things have one cell, but the human body consists of about a hundred trillion cells!

Almost all cells contain a nucleus. The nucleus is very important as it controls everything that happens inside the cell. Around the nucleus is a jelly-like substance called ‘cytoplasm’. Here, lots of chemicals are stored. Around the cytoplasm is a very thin ‘skin’ called the cell membrane? This holds the contents of the cell together and controls what enters and leaves the cell. Plants and animals have different types of cells. These cells are all designed for a particular job.

 

 

 

 

 

Plant cells

Plant cells are each surrounded by a ‘cell wall’ made of cellulose, which gives the plant structure and support. They each have a nucleus and cytoplasm. Plant cells usually have a very regular shape.

Animal cells

Animal cells don’t have any cell walls (just a cell membrane). This is because animals use other ways of supporting themselves, such as skeletons. Animal cells are usually irregular in shape.

 

 

 

 

 

 

Special cells have caused pigmentation in these zebras’ coats, creating a striped camouflage.

 

 

 

 

 

 

 

A leaf under a microscope clearly shows the structure of a plant cell.

Living things need certain substances to move, grow and keep themselves alive. Animals eat plants or other animals as their main source of nutrition.

This food is chemically complicated and must be reduced to simpler materials by a process called “digestion”. Chemicals in the body break down the nutrients in food, which the body then uses for growth and energy. Waste materials are then excreted by the body.

 

 

 

 

Photosynthesis

Plants and animals depend on each other for feeding and breathing. Plants take carbon dioxide from that air and absorb water and minerals from the soil. They use the Sun’s energy to convert these simple substances into sugars and starches and produce oxygen. This is called “photosynthesis”.

Animals, like gorillas, use plants as a source of food. They also breathe in the oxygen that plants release. Animals produce carbon dioxide which they breathe out and they excrete waste water and chemicals from their bodies. Plants depend on all these substances.

 

 

 

 

 

Plants need oxygen in order to carry out certain life processes. Plants use photosynthesis to produce oxygen but they also absorb oxygen from the soil (through their roots) and from the air (through small holes in their leaves).

 

At night, plants take oxygen from the air because there is not enough sunlight for photosynthesis to take place. During the day plants produce their own oxygen – much more than they need. This excess oxygen is released into the air.

 

Plants provide oxygen for humans and animals to breathe.

 

 

 

 

Squirrels need to eat about a pound of food a week to maintain an active life.

Most animals have to move to find their food and to avoid predators and other dangers. Many of these animals have muscles to help them move. Muscles help fish to swim, birds and insects to fly and many animals to walk and run.

Plants move by growing in different directions. When water is in short supply, plant roots grow deeper into the soil to find it. Shoots grow taller to find more sunlight. Plants also need to move their pollen and seeds. Pollen and seeds are ‘dispersed’ – spread around – from their parent plant so that they have their own space to grow. They may be carried by animals, water or the wind.

 

 

 

 

Most snakes get from place to place by throwing their bodies into curves. When a snake moves, waves of muscular contraction flow from head to tail. Its sides also push against irregularities on the ground (represented by the orange arrows in the diagram).

 

 

 

 

 

 

 

Virtually every part of a cheetah’s body has been adapted to maximize its running speed.

 

 

 

 

 

 

 

Climbing plants, like ivy, use walls for support, and grow towards the sunlight.