The atmosphere, which surrounds and sustains life, is the stage set within which the drama of weather played. Extending from the Earth’s surface to perhaps 965 kilometers or 600 miles or more into space, the atmosphere divides into several layers, each comprised of gases in varying quantities and densities, namely the troposphere, the stratosphere, the mesosphere, and the thermosphere.
The Moon is Earth’s next-door neighbor in space. Moon rocks are distinctly different from Earth rocks, and this difference suggests that the Moon was once hotter than the Earth has ever been and emphasizes that the Moon has no air and no water. The oldest rocks found on the Moon are 4.6 billion years old. The oldest rock yet discovered on Earth dates from only 3.8 billion years ago.
Earth is the planet we inhabit, a nearly spherical body which rotates every twenty-four hours from west to east around an imaginary line called its axis. The planet Earth, one of nine planets which circle the Sun, completes its revolution in about 365 days and 6 hours. It is the third planet from the Sun, and the only one we know that supports life. The planet Earth is nearly 4,600 million years old and most probably took over 100 million years to form into a ball of rock. The first tiny signs of growth appeared some 3,500 million years ago and life as we know it has evolved over the last 40 to 50 million years.
The water on the Earth’s surface that now fills our seas and oceans got there as part of a process that started with the origin of the Earth itself. The material from which the Earth and the other planets were later to be formed probably began as a cloud of gases spinning around the Sun. These gases gradually condensed, making solid particles. Many of them collided and built up larger and larger concentrations of matter.
The part that was eventually to become the Earth seems to have cooled and begun solidifying about 4.6 billion years ago and as the spinning movement shaped matter into a ball, it contracted even further. Under these pressures, matter at the center of the newly formed Earth began to heat up again and became molten. When this happened, water that had contained inside the Earth was released to the surface as vapor and added to the primitive atmosphere. When it cooled and condensed, it fell to the surface as rain and eventually formed the first oceans.
All the planets visible in the night sky are members of the Sun’s family or the solar system. Planets shine with a steady light while real stars often twinkle. This is because a planet is a disc of light, whereas a star is so distant that it is always just a point of light. The Sun is a typical star in that it radiates heat and light of its own, but the planets shine only by the light they reflect from the Sun. Most stars are much larger than planets. The five planets that can be seen without the aid of a telescope are Mercury, Venus, Mars, Jupiter, and Saturn. After the invention of the telescope, astronomers discovered three more distant planets – Uranus in 1781, Neptune in 1846 and Pluto in 1930.
To the planets, animals, and peoples of the Earth, the Sun is a unique and vital star. Every living thing on the Earth owes its existence to the fact that the Sun is nearby and keeps shining and has done so for about 5 billion years. The energy that comes from the burning of coal, oil and natural gas was once sun-energy. These fuels are the remains of plants and animals that grew in the warmth of sun-energy millions of years ago. The nearest star, apart from the Sun, is 300,000 times farther away and the weak star energy we receive from it cannot possibly replace sun-energy.
The selection of world facts and figures that follow provide the traveler with some background information on a world that seems to be more within our reach every day and a chance to look at this world as a whole before becoming engrossed in the more detailed country-by-country descriptions in the pages that you may find on this website.