The sun, the star at the centre of the Solar System, is a burning hot ball of shining gas. In it, every second, millions of ‘hydrogen bombs’ are exploding — turning hydrogen into helium.
The earth belongs to a family of eight planets, each of which is in orbit around the sun, which includes the moons orbiting around their planets, and lumps of rock called asteroids and comets with their long tails of dust and gas.
Among the eight planets and a ‘dwarf planet’ that orbit the sun, Mercury, Venus and Mars are rocky wastes. Jupiter, Saturn, Uranus and Neptune are globes of gas, pluto is classified as a ‘dwarf planet’ for its small size. Only the earth has water and enough oxygen to support animal and human life.
When the earth formed 460 crore years ago, it glowed red hot and the molten metals sank into the centre while the lighter rocks floated to the surface. Buried deep in the heart of our planet is a metal core of iron and nickel that is larger than the moon. The outer layer of the core is a liquid metal, but at the centre enormous pressure has compressed it into a solid one. Around the core, there is a thick layer of hot rock called the mantle. This acts as a heated blanket, holding in the warmth. Around the mantle is a third layer called the crust. The thickest parts of the crust are about 60 kilometres deep, and its surface is formed with rocks, clay and water on which we live.
The mantle contains traces of radioactive uranium which steadily gives out heat. This creates a more fluid part of the mantle known as the asthenosphere. Above the asthenosphere lies the lithosphere, which includes the outermost mantle and the crust. The lithosphere is made continental plates which float on the fluid asthenosphere. These plates are constantly moving, causing the continents to drift apart, mountains to form, the ground to shake, and volcanoes to erupt. Without the heat and light of the sun, the earth would be a frozen, dead world.
However, the earth has not always been how it is now. Soon after it formed as a gas ball, about 460 crore years ago, this planet was a big roasting cauldron. Over millions of years the surface cooled and the atmosphere, oceans and continents formed. Life began in the oceans about 3,500 million years ago with tiny, microscopic life-forms. Many scientists think that animals and plants started to live on the land about 400 million years ago. And then came the human beings through evolution.
This is our planet — our dear earth. But global warming due to our indiscriminate use of our environment is becoming an impending threat to us. Many species of flora and fauna may disappear from the planet. We must bear in mind — Pollute and perish, Preserve and flourish.