Millions of years ago the planet earth, a very tiny part of the universe, did not exist. It was about 4,600 million years ago that the planet earth and the other planets were formed around Sun that was till then just another star in the Solar system.
It happened when Gasses and other small particles of matter first came together and stick to each other to form a cloud. Gradually the cloud became a ball that began to heat from the inside, causing the matter to melt; and forming a crust on the outside. Gasses and steam that erupted from the hot liquid center formed water and atmosphere. Then the crust cooled and hardened and our planet earth came into being. The crust’s parts which were lying high became the continents and water accumulated in low-lying parts formed oceans.
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The shape of the Planet Earth
Throughout history, the shape of the planet earth has intrigued scientists. Even before the Middle Ages, people believed that the planet earth was flat. Although Pythagoras was the first person to announce that the planet earth is spherical, people did not accept his view and the concept of the planet earth being flat persisted till about 300 years ago. In fact, in those times, people did believe that if they sailed too far in one direction, they would fall off the earth.
It was Sir Issac Newton, a great English scientist, who was the first to claim that the planet earth is not ‘spherical’, but ‘oval’. Today it has become an established fact that the planet earth is not a perfect sphere; it is slightly flattened at the poles, and it swells at the equator because of the rapid spinning of the planet earth. In recent years the scientist have come to know that there is another small bulge at the North Pole; resultedly, the earth is now considered to be pear-shaped.
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The Planet earth’s crust
The outermost surface of the planet earth is termed the ‘crust’; its (the Crust’s) thickness varies from about 40 kilometers to about 10 kilometers.
It is about 40 kilometers thick beneath continents and 10 kilometers thick beneath oceans; it possesses only about 1 percent of the earth’s volume and ends at the next layer known as the mantle. The crust joins the mantle along a boundary called Mohorovicic discontinuity. Scientist often arranges the upper portion of the mantle, that at the top is as rigid as the crust, with the crust and call it the lithosphere.
The crust of the planet earth, contrary to the belief that it is a huge shell of solid rock, is in fact broken into 20 or so huge plates called tectonic plates which are always shifting due to which the cracks present in the crust keep widening and narrowing. Sometimes, when molten rock pushes up from the layer underneath the crust through these cracks, volcanoes are formed. It is very important to mention here that the planet earth is the only planet with its crust divided into moving plates.
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The earth’s mantle, that comprises approximately 70% of earth’s volume, is a 2,900 kilometers thick rocky shell. It is made up of two layers and lies under the crust.
The thickness of the outer part of the mantle is about 600 kilometers. The temperature of the mantle is 2000 degrees Celsius. It is composed of magma, the molten rock, that has the consistency of a hot tar. The inner layer of the mantle is more solid but not rigid, than the outer layer; it is like plastic and moves very slowly.
The core of the Planet Earth
The core, the heart, of the planet earth consists of a fluid outer core and a solid inner core. The outer core, having temperatures up to 3000 degrees Celsius, is made up of chiefly liquid iron that flows in the massive corkscrew-like currents, which produce the earth’s magnetic field.
The inner core of the planet earth is hotter than the outer core; its temperature can scale up to 5500 degrees Celsius, exuding tremendous pressure due to which the iron crystals in the inner core form a solid ball.
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Unique Feature of Earth as a planet
The planet earth is unique in the solar system as it is the only planet so far that has ever had a life of any kind. This may, of course, change in the future, but so far the earth is the only planet that supports life.
On earth life is possible because most of its surface is covered with water and atmosphere protects the planet from most of the sun’s dangerous radiation.
The atmosphere, the layer of gasses surrounding the planet earth, is made up of about 77 percent Nitrogen and about 21 percent Oxygen. Precisely, the planet earth is unique in that it is warm-but not boiling; cold-but not freezing all the time. Water covers three-fourth of its surface and its atmosphere possesses Oxygen; that is why in the solar system it is the only planet that has a life.
The Sun is just one of 100 billion stars arranged in a shape like fried egg. This huge star city is called the galaxy. The location of the planet earth in the solar system, galaxy, and Universe exhibits the difference between the lush, vibrant planet that the earth is and a barren wasteland, devoid of life.
The planet earth, just one planet whose distance from the Sun is just right to support life, is the third planet out from the sun, between Venus and Mars. Normally, on an average, the distance of the planet earth from the sun is of 148.8 million kilometers; however, the distance varies depending on the time of the year. The planet earth remains closest to the sun on January 3rd and it is known as perihelion; it is farthest away from the sun on July 4, and this is called aphelion.
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Formation of the Universe and Big Bang Theory
Scientists believe that the Universe began about 13 and 18 million years ago. According to some scientist, the Universe came into existence with an awesome explosion that they have named ‘the Big Bang’.
The Big Bang Theory deals with the explanation (of) what happened at the very beginning of the universe. Scientists are firm in their belief that the Universe came into existence at a specific point in time, and before that there was nothing. During and after that moment the Universe came into being, and the Big Bang Theory is considered an effort to explain what occurred during, and after that moment.
The universe, that is believed to have begun as an infinitesimally small, infinitely hot, and infinitely dense speck of matter, began to expand and burst in a gigantic explosion between 10 and 20 million years ago. This massive explosion called the Big Bang, hurled matter in every direction. Within a split second were created all the forces that shape the universe and all forms of matter.
The universe created by the Big Bang is still expanding and codling even to this day; the explosion was so massive that material is still hurtling away in all directions at amazing speeds.
According to some theorists, after the Big Bang, the universe was hotter than the Sun; there were no stars, but a burning soup of hydrogen nuclei and electrons that speeded around on their own.
As space stretched, the universe cooled that allowed the hydrogen nuclei to capture electrons and made, in the process, that is called neutral hydrogen. The early universe, therefore, was opaque, obstructing the release of light like morning fog.
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