Earth
Everyone you've ever met is from Earth. Unless you have something interesting to tell us. Earth is the prototype for terrestrial planets. It rotates fairly slowly. It consists of a mixture of rock and iron. Its interior is divided into layers, that is, differentiated. Like most terrestrial planets, Earth has a relatively thin atmosphere.
Earth is also special in so many ways. It is the only place in the universe where we know life to exist. We have liquid water in our oceans and free oxygen in our atmosphere, which was not at breathable levels until just a few hundred million years ago. Earth also has plate tectonics, which makes it a very interesting place to live, sometimes too interesting. This animation shows how the crust of Earth has floated around over the last 750 million years.
The interior of Earth is, of course, unexplored. However, we do have some sense of what goes on inside our planet. The main layers of importance are the core, the mantle and the crust. We have not yet been able to drill deep enough to reach the mantle of Earth, but one organization is close. Let's hope they don't make a Crack in the World.
The iron core of Earth generates an appreciable magnetic field around the planet. Charged particles from the Sun stream outward in what is called the solar wind and are trapped in a region known as the Van Allen belts, after the University of Iowa physicist who helped discover them last century. Here is a picture of the Van Allen belt. And here is a diagram of the Van Allen belts.
The atmosphere of Earth can be divided into distinct layers. One benefit our atmosphere is that it blocks certain harmful types of radiation. The surface temperature on Earth can vary quite a bit but is between -20 degrees Celsius and 40 degrees Celsius most of the time, making liquid water a common thing at the surface.
The most prominent surface feature on Earth is ocean. There are large, ancient craters to be found here and there. Most notable is the giant Chicxulub crater, which is thought to have been involved in the mass extinction of 65 million years ago. Why are there so few craters on the continents of Earth? It is not because we have not been hit in the past.
Here are the essential facts about the Earth
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Updated 10/6/2010