Earth is the third planet from the Sun and the only planet currently known to harbor life. It has a molten core that generates a protective magnetic field that shields against the solar wind and flares. Earth is the only planet that has surface water.

Tectonic plates float on the hot magma just below the solid rocky crust of the Earth. These plates make up the continents of Earth and have shifted over time, creating mountain ranges and causing earthquakes. For example, Africa and South America were once adjacent, but are now separated by the Atlantic Ocean.

The Moon is the largest moon in the solar system relative to its planet. Overall, our Moon is similar to the magma of the Earth. It was formed by a gigantic impact with another planet early in the solar system that blasted magma and crust into orbit around the Earth. That material pulled together via gravity and the Moon was formed. The Moon stabilizes the tilt of the Earth, helping the development of life.

Rocks returned from the Apollo missions date the Moon to 4.5 billion years. This is consistent with primordial meteorites that date the Solar System to 4.6 billion years.

Water on Earth was delivered by impacts of comets and icy asteroids in the early era of the Solar System. There is evidence that the amino acids found in comets may have provided the building blocks for early life on Earth.

  • Earth
  • Moon
  • Earth Symbol
Orbit Specifications
Semi-major axis 1.496 x 108 km
1.00000261 AU
Eccentricity 0.012
Orbital Period 365.2563 d
Physical Characteristics Specifications
Mean radius 6,371 km
0.533 Earths
Mass 5.97219 x 1024 kg
3.0 x 10-6 Suns
Mean density 5.515 g/cm3
Surface gravity 9.780327 m/s2
0.99732 g
Axial tilt 23° 26' 21.4119''
Moon Specifications
Radius 1,737.4 km
Mass 7.349 x 1022 kg
Semi-major axis 384,400 km
Orbital period 27 d 7 h 43.7 m