About Planet Earth - Introduction

Earth is the fifth largest planet in the Solar System.
The Earth is around 4.6 billion years old.
Earth is the only presently known planet in the Solar System to support life. The earliest fossil evidence for life dates back 3.5 billion years ago.
71% of Earth's surface is covered in water.
The Earth is the densest planet in the Solar System.
The Earth travels at an orbital speed of 108,000 km (67,000 miles) an hour.
The Earth has only one satellite,the Moon.The Moon is the second brightest object in the sky.
The Earth's atmosphere is composed mainly of nitrogen (77%), oxygen (21%), argon (.93%), and carbon dioxide (0.03%).
The surface features on Earth are extremely varied with vast oceans, tall mountains, rolling plains, canyons, swamps, and deserts. The tallest mountain on our planet, Mount Everest in the Himalayas, stands at an altitude of 8,872 m (29,108 ft). Located in Africa, the Sahara, the largest desert on Earth, spans over 500,000 sq km (2,123,000 sq miles) of land. The Grand Canyon, a canyon of multi covered rock terraces cut by the Colorado River, stretches over 350 km (217 miles) of land.
71% of the Earth's surface is coverered in water, which holds vast amounts of ocean life and maintains the temperature of the planet.
Earth has an average surface temperature of 13 degrees C (55.4 degrees F). The planet would be much colder without greenhouse gasses, such as carbon dioxide and water vapor,to trap outgoing thermal radiation. The greenhouse effect raises the planet's temperature 35 degrees C (95 degrees F).