Earth

Earth is the third planet from the sun. Earth is the largest of all the planets in our Solar System. It is unique because it is the only planet that is fit for sustaining life. It is the home to about 7 billion people and is made up of 30% land and 70% water. The Earth uses the Sun to provide it with warmth, light, and energy. If the Sun were hollow, we could fit one million Earth-sized planets inside of it! The Earth's atmosphere is one of the main factors that makes life on the planet possible. The Earth's atmosphere is made up of three primary gases: oxygen, nitrogen, and argon. The atmosphere extends outward from the planet for almost 6,000 miles but most of the atmosphere is packed into the first 16 miles. The higher a person travels, the less packed the atmosphere becomes. This means that the higher you go the lighter you become! Also, there are many gases that effect the Earth's weather patterns. Carbon dioxide is one of these gases that absorbs heat and helps keep the Earth warm enough for life to exist. Another important gas found in the Earth's atmosphere is ozone which is made up of oxygen. The ozone acts as a giant sheet of sunscreen, absorbing the sun's radiation to protect the planet's plants and animals. The Earth also has what is known as a water cycle or the hydrologic cycle. The water cycle regulates the planet's water moving it throughout the land and sky. The Earth's biosphere is defined as the area around the planet where life exists. This area is very large and consists of different cycles and biomes that maintain the balance of life.
 * All About Earth**

**Astronomy Mythology**: In Roman mythology, Earth was the mother of the mountains, valleys, streams and all other land formations. Her Greek name was Gaea and she was married to Uranus.

Distance from the Sun: 150 million kilometers 1 Orbit around the Sun: 365.3 days 1 Full Rotation: 23 hours 56 minutes Average Temperature: 45 degrees F Moons: 1 moon, Luna
 * Fast Facts:**

Earth's moon, Luna, is covered with mountains, valleys, old volcano sites, and many bowl-like holes called craters. It is located about 384,400 kilometers away from the Earth. Luna is unique because it can be seen from Earth without the use of a telescope. The Earth's moon regulates the ocean tides and keeps the Earth's tilt on its axis regular. This is why we have seasons on Earth. When the North Pole is tilted towards the sun, then the Northern Hemisphere is in its warmer seasons and the Southern Hemisphere is in its colder seasons. When the South Pole is tilted towards the sun, then the Southern Hemisphere has its warmer seasons and the Northern Hemisphere is colder. Also, Luna is very close in size to the Earth which is why many scientists consider the two to be a double planet system.
 * Earth's Moon**

Scientists use the Earth to study all of the other planets. Since human life cannot exist on any other planet, we have to use what we know about the Earth to try to guess what the other planets are be like. This is called Comparative Planetology.
 * Did you know?**