Facts about Earth
Introduction to our Planet's Atmosphere and Interior Layers
Earth is remarkable because it is currently the only planet we know in the entire universe to harbor life.
Earth is the third of the four terrestrial (rocky) planets and the largest in size, at 12,756 kilometers in diameter. It has one large moon, which is unique among the other inner planets. Mercury and Venus have no moon and Mars has two small ones that are captured asteroids.
Earth takes approximately 365 days to orbit the Sun once, thus equalling one Earth year. Earth spins on its axis in approximately 24 hours, thus equalling one Earth day.
Information about Our Atmosphere
Earth's atmosphere is composed of 77% nitrogen, 21% oxygen, and traces of argon, carbon dioxide, and water. The atmosphere is about 560 kilometers thick and consists of different layers. Each layer gets thinner as you move away from Earth. The layer closest to the surface is called the troposphere. It extends upward to about 20 kilometers. Above this is the stratosphere to 50 km, the mesosphere to 85 km, the thermosphere to 690 km, and the exosphere to 10,000 km where the solar wind takes over. Space shuttles orbit in the thermosphere and this is also where much auroral activity takes place. Temperatures of the atmosphere near the surface can range from -90 degrees Fahrenheit to over 120.
This Terrestrial Planet's Interior Layers
Earth began forming about 4.6 billion years ago along with the rest of the solar system. The outer surface of Earth is called the crust, and it extends down to about 40 kilometers before it switches to mantle. The mantle is sometimes divided into two parts, the upper and lower mantle. The mantle reaches down to about 2800 kilometers before the core begins. The core can also be divided into two parts, the inner and outer core.
The thickness of the crust varies depending on location. Under land mass and mountains the crust is thicker, where deep in the ocean it is thinner. The crust is solid, as well as the inner core, but the other layers are more fluid and molten. The core is believed to be made mostly of iron with temperatures ranging up to 7500 Kelvins.
Plate Tectonics
Earth's crust consists of plates that are constantly shifting. As they pull apart and push together, earthquakes occur. Over the history of Earth the land masses have wandered significantly as they came together and broke apart, before ending up with what we see now. They are continuing to change daily.
