No human areas of reasoning are infallible and discussions of the universe as a whole are filled with uncertainty. The ancient Egyptians theory of the universe of varied with that of the Chinese, of the Mayan and so on. Initially assuming that the Earth was flat ancient astronomers later believed in a universe with the Earth at its center and a vast sphere revolving around it. On the inner surface of this sphere lay the stars. As man evolved, so did the theories. Bishop James Ussher referring to the Old Testament placed the creation in the year 4004 BC. Galileo Galilei disagreed stating that the Bible teaches us how to go to heaven, not how the heavens go. In 240 BC Eratosthenes estimated the circumference of Earth to be about 42,000 km. In 1492 Christopher Columbus derived the distance to be 29,000 km. It is actually 40,075 km.
Earth is the only planet in the Solar System where life is known to have evolved. For long, we have been taking our rock solid planet Earth beneath our feet for granted. It has always been a comforting illusion that we are safe from the hazards of the universe as long as our feet are planted on the solid surface of Earth. However we fail to realize that seemingly solid surface of the Earth is actually composed of a series of drifting plates. Since the time it was formed 4.6 billion years ago, the Earth was probably solid throughout, but 500 million years of radioactive decay heated the Earth causing the metallic material to melt and separate from the non-metallic silicate material. The metallic material sank towards the center of the Earth pushing the silicate ones up. The molten material now 4200 miles in diameter is known as the core. The constant motion of this magnetic field gives the Earth its magnetic field. The layer on the outer part of the core is known as mantle, 1800 miles thick. Covering the mantle is crust. The outer crust of the Earth called lithosphere is divided into seven major plates and twelve minor ones each approximately 60 miles resting on a less stable softer layer called asthenosphere. Imbedded in these plates are the continents surrounded by mass of water called oceans.
Transfer of heat energy within the Earth cause the plates to drift in the process of which they collide & either slip over or under. In some cases they grind or drift apart. It is along the boundaries of such collisions the earthquakes & volcanoes occur. Last month's earthquake at Gujarat killed thousands. Avalanches & landslides, cyclones, famines, floods, epidemics, tornadoes etc. along with earthquakes & volcanoes are the mass destruction machinery on Earth. Sometimes it seems as if nature's design to control the world's population. Others like a comet or asteroid impact make it appear to be a cruel cosmic joke. The very randomness and suddenness of some natural disasters are sometimes their most devastating qualities. The destruction of dinosaurs, volcano at Pompeii, Armenia earthquake, Bengal famine, cyclone in Andhra Pradesh, China's Yellow River floods. If it was Black Death during Middle Ages now it's AIDS.
Man's economic activities have involved all of nature's subsystems - the biosphere, atmosphere, hydrosphere & lithosphere to an extent that they may be compared with the above disasters. Billions of tons of organic & non-organic substances are used for material production. The consumption of oxygen in this process leads to reduction of its total volume in the atmosphere, the rate of carbon dioxide emission from burning of fossil fuel is more than its absorption by plants & sea water, aerosols emission exceeds the emission from a volcanic activity. Oil spills from ocean tankers is more than the amount of oil coming naturally from the lithosphere. The list is endless. The only consolation is the ban of Nuclear Tests in outer space.
A the year 1994 late Carl Sagan, the famous astronomer wrote a book entitled Pale Blue Dot. It contained a Voyager photograph of Earth, which was a single pixel - a pale blue dot. He wrote "On [that dot] everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives ... The Earth is a very small stage in a vast cosmic arena. Think of the rivers of blood spilled by all those general and emperors so that, in glory and triumph, they could become the momentary masters of fractions of a dot".
Think of it, the Earth however big it may seem is just a dot & yet as on date, the only one we have.
