Formation of Our Solar System

Many scientists believe that our solar system was formed from a giant, rotating cloud of gas and dust known as the solar nebula. According to this theory, the solar nebula began to collapse because of its own gravity. Some astronomers speculate that a nearby supernova (exploding star) triggered the collapse. As the nebula contracted, it spun faster and flattened into a disk.

The nebular theory indicates that particles within the flattened disk then collided and stuck together to form asteroid-sized objects called planetesimals. Some of these planetesimals combined to become the nine large planets. Other planetesimals formed moons, asteroids and comets. The planets and asteroids revolve around the sun in the same direction, and in more or less the same plane, because they were originally formed from this flattened disk.

Most of the materials in the solar nebula, however, was pulled toward the center and formed the sun. According to the theory, the pressure at the center became great enough to trigger the nuclear reactions that power the sun. Eventually, solar eruptions occurred, producing a solar wind. In the inner solar system, the wind was so powerful, that it swept away most of the lighter elements - hydrogen and helium. In the outer regions of the solar system, however, the solar wind was much weaker. As a result, much more hydrogen and helium remained on the outer planets. This process explains why the inner planets are small, rocky worlds and the outer planets, except for Pluto, are giant balls composed almost entirely of hydrogen and helium.

Earth

The earth is a huge sphere. The surface of which is made up of rock, soil and water. It is surrounded by air. The planet earth is only a tiny part of the universe, but it is the home of human beings and many other living things. Animals and plants live almost everywhere on the earth's surface. They can live on the earth because it is just at the right distance from the sun. Living things need the sun's warmth and light for life. If the earth were to be too close to the sun, it would be too hot for living things. If the earth were to be too far from the sun, it would be too cold for any organism to survive. Both plants and animals need water to survive, which the earth has in plenty. Water covers most of the earth's surface (about 81%).

Earth

A thin layer of rock called the crust forms the earth's surface. All life on the earth is found on this crust or in the water that covers about 70 percent of it. Beneath the crust is hot rock. A ball of molten metal lies at the center of the earth.

The earth ranks fifth in size among the planets. It has a diameter of about 13,000 kilometers. The earth is about 150 million kilometers from the sun. The atmosphere of the earth contains enough oxygen to support animal life.

Earth has three types of motion:

• It spins like a top

• It travels round the sun

• It moves through the Milky Way with the rest of the solar system