There is no other planet in our Solar system quite as beautiful when viewed from space as the planet Earth.
Earth has a diameter of 12,800 km and a mass of 6.0 x 1024 kg. It is the third planet from our sun.
According to data obtained through radioactive dating, the Earth is estimated to be approximately 4.6 billion years old.
Earth is a terrestrial planet, which means that it is made up of rock as opposed to gaseous substances. Earth's structure is divided up into 4 main components. Earth's surface is called the crust. The oceans, which comprise 70% of Earth's surface, are called the hydrosphere. Earth's hydrosphere is clearly visible form outerspace, and contributes to the beauty of the planet when viewed from space (and here on Earth too!).
Underneath Earth's crust and hydrosphere is the mantle. Underneath the mantle is Earth's core.
Above the Earth's surface, we have the atmosphere, and at very high altitudes we have the magnetosphere, which is trapped by Earth's magnetic field.
Earth is certainly special in that it is the only planet that we know of that supports life. It is also the only planet in our solar system that has abundant liquid water, moderate temperatures, and an oxygen (21%) atmosphere.
Earth's atmosphere prevents us from having wild temperature swings. Our atmosphere and magnetosphere also helps protect us from radiation from the sun, and from falling near Earth objects. Near Earth objects are objects like asteroids or meteoroids that typically burn up on their descent through Earth's oxygen atmosphere and therefore don't usually make it all of the way to Earth's surface.
Earth is a fantastic planet, teaming with life, and we really should take better care of it.
Why is there life on Earth, but nowhere else that we know of? Most scientists believe that the presence of water is necessary to support life. Also, the temperature range on Earth is just right. If Earth were closer to, or further away from the Sun, then Earth would be either too hot or too cold to support life. Earth is located 150 million km (93 million miles) from the sun (Dutch, 2004). As it turns out, the temperature conditions on Earth are just right to support many different life forms. This is not only because of our location in reference to the sun, but also the thickness of our atmosphere is perfect. If our atmosphere was much thicker, Earth might be too hot to support life, but if our atmosphere was thinner, it might be too cold to support life.
Earth's Orbit and Rotation
Every 24 hours Earth rotates on its axis (counterclockwise). Earth also orbits the sun in a counterclockwise direction. It takes Earth about 365 days to make one complete orbit around the sun. As you can see, our time conventions are based on Earth's rotation and orbit.
Dutch, Steven I. "Earth." World Book Online Reference Center. 2004. World Book, Inc. http://www.worldbookonline.com/wb/Article?id=ar171540.
Photo of Earth: Courtesy of NASA Glenn Research Center.