- The word "Earth" comes from the Old English word "ertha," meaning ground or land.
- Despite what is commonly believed, the Earth has been known to be (roughly) spherical since antiquity.
- Earth is the only known body in the universe to possess life.
- Until the 16th century the Earth was believed to be the center of the universe, with all objects orbiting around it.
Earth's atmosphere is composed of 78% nitrogen, 21% oxygen, and trace amounts of other gases including argon and carbon dixoide.
- The substantial amount of oxygen found on Earth is the result of plantlife's comsumption of carbon dixoide during the process of photosynthesis.
- An important component of Earth's atmosphere is the Ozone Layer—a "shell" of a special type of oxygen that protects the Earth from harmful solar radiation.
- Oceans cover over 70% of Earth's surface.
The first life on Earth developed in the oceans.
- Earth's water was initially trapped within the planet; however, over time this water was brought to surface as a result of the planet's volcanic activity.
- Only 30% of Earth's surface is dry land.
- Compared with other solid bodies in the Solar System, the Earth's surface has realtively few visible impact craters. The lack of craters is due to Earth's geological processes reshapping its surface.
Earth's highest point is Mount Everest. Its height is 8.8 km.
Earth's lowest point is Challenger Deep, found 10.9 km beneath sea level.
- Earth is the fifth largest planet in the Solar System, and largest of the terrestrial planets.
- The orbit of Earth is one of the most circular of all the planets.
- One year on Earth last a little over 365 days. This "little over" part is almost 1/4 of a day, and hence the reason we have a leap year every 4 years.
- The axis around which Earth rotates is tilted 23°. The effect of this tilt is the different seasons we experience.