Our home planet is the third planet from the Sun, and the only place we know of so far that’s inhabited by living things.
While Earth is only the fifth largest planet in the solar system, it is the only world in our solar system with liquid water on the surface. Just slightly larger than nearby Venus, Earth is the biggest of the four planets closest to the Sun, all of which are made of rock and metal.
The name Earth is at least 1,000 years old. All of the planets, except for Earth, were named after Greek and Roman gods and goddesses. However, the name Earth is a Germanic word, which simply means “the ground.”
Since the Copernican revolution of the 16th century, at which time the Polish astronomer Nicolaus Copernicus proposed a Sun-centred model of the universe (see heliocentric system), enlightened thinkers have regarded Earth as a planet like the others of the solar system.
Concurrent sea voyages provided practical proof that Earth is a globe, just as Galileo’s use of his newly invented telescope in the early 17th century soon showed various other planets to be globes as well. It was only after the dawn of the space age, however, when photographs from rockets and orbiting spacecraft first captured the dramatic curvature of Earth’s horizon, that the conception of Earth as a roughly spherical planet rather than as a flat entity was verified by direct human observation.
Humans first witnessed Earth as a complete orb floating in the inky blackness of space in December 1968 when Apollo 8 carried astronauts around the Moon. Robotic space probes on their way to destinations beyond Earth, such as the Galileo and the Near Earth Asteroid Rendezvous (NEAR) spacecraft in the 1990s, also looked back with their cameras to provide other unique portraits of the planet.
The earth is made up of three different layers: the crust, the mantle and the core.
The Crust
This is the outside layer of the earth and is made of solid rock, mostly basalt and granite. There are two types of crust; oceanic and continental. Oceanic crust is denser and thinner and mainly composed of basalt. Continental crust is less dense, thicker, and mainly composed of granite.
The mantle
The mantle lies below the crust and is up to 2900 km thick. It consists of hot, dense, iron and magnesium-rich solid rock. The crust and the upper part of the mantle make up the lithosphere, which is broken into plates, both large and small
The core
The core is the centre of the earth and is made up of two parts: the liquid outer core and solid inner core. The outer core is made of nickel, iron and molten rock. Temperatures here can reach up to 50,000 C.
Also,Earth's atmosphere is composed of about 78 percent nitrogen, 21 percent oxygen, 0.9 percent argon, and 0.1 percent other gases. Trace amounts of carbon dioxide, methane, water vapor, and neon are some of the other gases that make up the remaining 0.1 percent.
Viewed from another planet in the solar system, Earth would appear bright and bluish in colour.
Easiest to see through a large telescope would be its atmospheric features, chiefly the swirling white cloud patterns of midlatitude and tropical storms, ranged in roughly latitudinal belts around the planet. The polar regions also would appear a brilliant white, because of the clouds above and the snow and ice below.
Beneath the changing patterns of clouds would appear the much darker blue-black oceans, interrupted by occasional tawny patches of desert lands. The green landscapes that harbour most human life would not be easily seen from space. Not only do they constitute a modest fraction of the land area, which itself is less than one-third of Earth’s surface, but they are often obscured by clouds.
Over the course of the seasons, some changes in the storm patterns and cloud belts on Earth would be observed. Also prominent would be the growth and recession of the winter snowcap across land areas of the Northern Hemisphere.
Scientists have applied the full battery of modern instrumentation to studying Earth in ways that have not yet been possible for the other planets; thus, much more is known about its structure and composition. This detailed knowledge, in turn, provides deeper insight into the mechanisms by which planets in general cool down, by which their magnetic fields are generated, and by which the separation of lighter elements from heavier ones as planets develop their internal structure releases additional energy for geologic processes and alters crustal compositions.
When it comes to Earth's atmosphere, we'll weather the weather, whatever the weather, whether we like it or not.
Earth is the only planet in the solar system with an atmosphere that can sustain life. The blanket of gases that surrounds our home planet not only contains the air that we breathe but also protects us from blasts of heat and radiation emanating from the sun. It warms the planet by day and cools it at night.
Rotation
An observer in space will see that Earth requires 23 hours, 56 minutes, and 4 seconds to make one complete rotation on its axis. But because Earth moves around the Sun at the same time that it is rotating, the planet must turn just a little bit more to reach the same place relative to the Sun. Hence the length of a day on Earth is actually 24 hours. At the equator, the Earth rotates at a speed of about 1,700 km per hour, but at the poles the movement speed is nearly nothing.
Revolution
For Earth to make one complete revolution around the Sun takes 365.24 days. This amount of time is the definition of one year.
The gravitational pull of the Sun keeps Earth and the other planets in orbit around the star. Like the other planets, Earth’s orbital path is an ellipse so the planet is sometimes farther away from the Sun than at other times.
The closest Earth gets to the Sun each year is at perihelion (147 million km) on about January 3rd and the furthest is at aphelion (152 million km) on July 4th.
Earth’s elliptical orbit has nothing to do with Earth’s seasons.During one revolution around the Sun, Earth travels at an average distance of about 150 million km. Earth revolves around the Sun at an average speed of about 27 km (17 mi) per second, but the speed is not constant. The planet moves slower when it is at aphelion and faster when it is at perihelion.The reason the Earth (or any planet) has seasons is that Earth is tilted 23 1/2oon its axis. During the Northern Hemisphere summer the North Pole points toward the Sun, and in the Northern Hemisphere winter the North Pole is tilted away from the Sun.