Earth is the third planet from the Sun in the solar system. Earth's average distance from the Sun is 92,900,000 mi (149,476,000 km), and defines one astronomical unit. Earth is an oblate spheroid with a surface area of 196,938,800 square miles (510,485,000 square kilometers). The elliptical orbit of Earth around the Sun takes approximately 365.26 days with respect to the background stars, and defines one sidereal year. Radiometric dating has led to a widely accepted date for Earth's age of about 4.6 billion years.

The bulk of scientific knowledge about Earth has accumulated only within the past few centuries and has evolved into the disciplines of geophysics and geology. Geophysics is the study of Earth as a planet and the space surrounding it, and the interactions between Earth and extraterrestrial forces. Geophysics contains three major divisions of study: the solid-earth, the atmosphere and hydrosphere, and the magnetosphere.

Solid-earth studies are concerned with...