Earth
Planet
Facts
- Diameter
- 12,756 km
- Mean distance from the Sun
- 149.6 million km
- Orbital period
- 365.2 days
- Rotation
- 23.9 hours
- Axial tilt
- 23.4°
- Atmosphere
- 78% nitrogen, 21% oxygen
- Age
- about 4.5 billion years
Earth is the third planet from the Sun and, as far as we know, the only place in the universe that hosts life. It lies in the so-called habitable zone, the band where temperatures let water stay liquid on the surface: oceans cover about 71% of the planet.
It is also the densest planet in the Solar System. Its iron and nickel core, partly molten, generates a magnetic field that surrounds it like a shield, deflecting the solar wind and protecting the atmosphere. The auroras are the visible sign of this invisible defence.
The atmosphere, 78% nitrogen and 21% oxygen, has not always been like this. Oxygen is a “waste product” of life: about 2.4 billion years ago cyanobacteria, through photosynthesis, released so much of it that they changed the planet's chemistry for ever.
Earth's surface is also constantly on the move. The crust is broken into plates that slide slowly over the mantle, raising mountains, opening oceans and recycling rocks in a cycle that no other known planet shows in this form.
Sources
- NASA NSSDC, Planetary Fact Sheet (Metric)
- NASA Science, Earth: Facts
- NASA Science, What is the habitable zone or “Goldilocks zone”?
- NASA Science, Earth's Magnetosphere: Protecting Our Planet from Harmful Space Energy
- NASA Astrobiology, Antarctic Microbes Hold Clue to Earth's Oxygen
- NASA Science, Basics of Space Flight, Chapter 1: The Solar System
- USGS, This Dynamic Earth: Understanding plate motions