Earth
Earth is the third planet from the Sun and the only known world that supports life. Its unique combination of liquid water, a breathable atmosphere, and a protective magnetic field make it an oasis in the vastness of space. Earth is the largest of the four rocky planets and the densest planet in the solar system.
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- Diameter
- 12,756 km
- Mass
- 1 Earths
- Distance from Sun
- 1 AU
- Surface gravity
- 9.81 m/s²
- Average temperature
- 15°C
- Known moons
- 1
- Orbital period
- 365.3 Earth days
- Rotation period
- 23.9 hours
- Ring system
- No
Source: NASA Planetary Fact Sheets (nssdc.gsfc.nasa.gov)
Atmosphere
Nitrogen (78%), oxygen (21%), argon (0.9%), carbon dioxide (0.04%). Supports life and creates weather.
In Depth
Earth stands alone in the known universe as a cradle of life. Our planet's habitability depends on a remarkable combination of factors: a distance from the Sun that allows liquid water to exist (the 'habitable zone'), an atmosphere thick enough to retain heat but thin enough to allow sunlight through, and a magnetic field strong enough to deflect the solar wind. Earth's surface is 71% water — the oceans contain about 1.335 billion cubic km of water. Active plate tectonics recycle the crust, regulate the carbon cycle, and build mountains. The atmosphere is primarily nitrogen and oxygen, a composition maintained by biological processes. Earth's single large moon stabilizes the planet's axial tilt at about 23.4°, giving us predictable seasons. The planet's liquid iron outer core generates a magnetic field extending thousands of kilometers into space, forming the magnetosphere that shields all surface life from harmful solar and cosmic radiation. Earth formed about 4.54 billion years ago, and the earliest evidence of life dates to roughly 3.7 billion years ago.
Notable Features
- 01
The only known planet to harbor life
- 02
71% of the surface covered by liquid water oceans
- 03
A strong magnetic field generated by a liquid iron outer core
- 04
Active plate tectonics constantly reshaping the surface
Exploration & Missions
Earth is the most studied planet in the solar system. Thousands of satellites orbit it, monitoring weather, climate, land use, and ocean conditions. The first photograph of Earth from space was taken in 1946 from a V-2 rocket. The iconic 'Blue Marble' photo taken by Apollo 17 astronauts in 1972 became one of the most reproduced images in history. NASA's Earth Observing System includes missions like Terra, Aqua, and the Landsat series, providing continuous global observations since the 1990s. The ISS has orbited Earth continuously since 2000 with human crews aboard.
Fun Facts
Earth is the densest planet in the solar system at 5.51 g/cm³, largely due to its iron-nickel core.
The deepest point on Earth — Challenger Deep in the Mariana Trench — is 10,935 meters below sea level, deeper than Mount Everest is tall.
Earth's rotation is gradually slowing: days were about 22 hours long 600 million years ago.
About 97% of Earth's water is saltwater; only 3% is fresh, and most of that is locked in ice caps.
Frequently Asked Questions
Why is Earth called the Blue Planet?▾
When viewed from space, Earth appears predominantly blue because its oceans cover about 71% of the surface. Water absorbs red wavelengths of light and reflects blue wavelengths, giving the planet its distinctive color. The nickname was popularized after astronauts first saw Earth from space.
How old is Earth?▾
Earth is approximately 4.54 billion years old, determined by radiometric dating of meteorites and the oldest known Earth rocks. The oldest mineral grains (zircons) found on Earth are about 4.4 billion years old, suggesting the crust formed relatively quickly after the planet's formation.
What protects Earth from the Sun's radiation?▾
Earth has two main shields. The magnetic field (magnetosphere) deflects most charged particles from the solar wind. The ozone layer in the stratosphere absorbs about 97-99% of the Sun's harmful ultraviolet radiation. Together, they make the surface safe for life.
Learn More
The 8 Planets in Order: An Interactive Guide for Students — an in-depth article covering all 8 planets, with size comparisons and learning activities.
Data source: NASA Planetary Fact Sheets
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