Why life exists

Our sun seems big and important to us. But really it is no different form all the stars what we see as tiny points of light in the night sky. The stars seem so small because they are so far away but some are actually much bigger than our sun.Some are older, and some are younger. By studying the star scientists can guess how our sun, and the planets that circle round it, were formed.

Formation of star
They all probably formed about 4,600 million years ago, and started as an enormous spinning cloud of gas. Gradually, the gases at the center of the cloud condensed together to form the plants. The outer planets, which lie far from the light and warmth of the sun, are called masses of gas and ice. The inner planets lying closer to the sun are very hot. The earth, too was very hot when it first formed. It which gradually cooled and turned to liquid. Then a solid crust of rock formed on its surface. Even today, the inside of the earth is still hot, and when volcanoes erupt they throw out molten rock which we call lava.
The atmosphere of the earth at first contained gases such as hydrogen, carbon dioxide, methane and ammonia. Water, too, was only a steamy vapour in the air. It look millions of years for the first rain to form. Only then cloud streams and river appear. The seas and oceans formed when pools of water gradually ran together.

The beginning of life
Many types of chemical together were dissolved in these warm water. When lightning from storms struck into the water, electrical energy linked the chemical together in many different ways. Eventually, a chemical appeared that could make more molecules like itself. That was the beginning of life. Scientists believe that this first form of life appeared about 3,000 million years ago.

The first living things
The earliest types of life must have been quite tiny and simple, like bacteria. They probably got their energy from breaking down other complex chemical around them. Some of these early living things evolved a green chemical that absorbed the energy from the sunlight in order to make their own food. These were the first plants and must have been like microscopic single-celled algae. Animals cannot make food. They get their energy from eating plants or eating other animals. So they could only evolve after the first plants, perhaps 1,000 million years ago. these first animals were tiny single-celled organisms.
Every living organism must be able two things. It must be able to use energy to make more of its own body chemicals so that it can grow. And it must able to reproduce, making more organism, each like itself.

Evolution
Each pair of animals or plants can produce very many offspring, but in each generation most of the offspring die before they grow up. That is why scientists speak of a " struggle for survival ".
Though each organism is very like its parents, no two organisms are quite identical. Perhaps one plant may be able to grow a little faster, or one animal may be able to run a bit further than its brothers and sisters. Any animal or plant with such an advantage is more likely to be able to survive to grow up and produce its own offspring. In this way, by the " natural selection " of those with advantages, animals and plants gradually change or " evolve " over many generations.