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Earth - Our Home
Our home planet is the third planet from the Sun, and the only place we know of so far that’s inhabited by living things. While Earth is only the fifth largest planet in the solar system, it is the only world in our solar system with liquid water on the surface. Just slightly larger than nearby Venus, Earth is the biggest of the four planets closest to the Sun, all of which are made of rock and metal.
Namesake
The name Earth is at least 1,000 years old. All of the planets, except for Earth, were named after Greek and Roman gods and goddesses. However, the name Earth is a Germanic word, which simply means “the ground.”
Potential for Life
Earth
Earth has a very hospitable temperature and mix of chemicals that have made life abundant here. Most notably, Earth is unique in that most of our planet is covered in liquid water, since the temperature allows liquid water to exist for extended periods of time. Earth's vast oceans provided a convenient place for life to begin about 3.8 billion years ago.
Some of the features of our planet that make it great for sustaining life are changing due to the ongoing effects of climate change.
Size and Distance
With a radius of 3,959 miles (6,371 kilometers), Earth is the biggest of the terrestrial planets and the fifth largest planet overall.
From an average distance of 93 million miles (150 million kilometers), Earth is exactly one astronomical unit away from the Sun because one astronomical unit (abbreviated as AU), is the distance from the Sun to Earth. This unit provides an easy way to quickly compare planets' distances from the Sun.
It takes about eight minutes for light from the Sun to reach our planet.
Atmosphere
Near the surface, Earth has an atmosphere that consists of 78% nitrogen, 21% oxygen, and 1% other gases such as argon, carbon dioxide, and neon. The atmosphere affects Earth's long-term climate and short-term local weather and shields us from much of the harmful radiation coming from the Sun. It also protects us from meteoroids, most of which burn up in the atmosphere, seen as meteors in the night sky, before they can strike the surface as meteorites.
Moon
Our satellite
Magnetosphere
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Core
Our planet's rapid rotation and molten nickel-iron core give rise to a magnetic field, which the solar wind distorts into a teardrop shape in space. (The solar wind is a stream of charged particles continuously ejected from the Sun.) When charged particles from the solar wind become trapped in Earth's magnetic field, they collide with air molecules above our planet's magnetic poles. These air molecules then begin to glow and cause aurorae, or the northern and southern lights.
The magnetic field is what causes compass needles to point to the North Pole regardless of which way you turn. But the magnetic polarity of Earth can change, flipping the direction of the magnetic field. The geologic record tells scientists that a magnetic reversal takes place about every 400,000 years on average, but the timing is very irregular. As far as we know, such a magnetic reversal doesn't cause any harm to life on Earth, and a reversal is very unlikely to happen for at least another thousand years. But when it does happen, compass needles are likely to point in many different directions for a few centuries while the switch is being made. And after the switch is completed, they will all point south instead of north.
10 Need-to-Know Things About Earth
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MEASURING UP
If the Sun were as tall as a typical front door, Earth would be the size of a nickel
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WE'RE ON IT
Earth is a rocky planet with a solid and dynamic surface of mountains, canyons, plains and more. Most of our planet is covered in water.
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RINGLESS
Earth has no rings.
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THIRD ROCK
Earth orbits our Sun, a star. Earth is the third planet from the Sun at a distance of about 93 million miles (150 million km).
BREATHE EASY
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Earth's atmosphere is 78 percent nitrogen, 21 percent oxygen and 1 percent other ingredients—the perfect balance to breathe and live.
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ORBITAL SCIENCE
Many orbiting spacecraft study the Earth from above as a whole system—observing the atmosphere, ocean, glaciers, and the solid earth.
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PROTECTIVE SHIELD
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AS THE WORLD TURNS
A day on Earth is 24 hours. Earth makes a complete orbit around the sun (a year in Earth time) in about 365 days.
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OUR COSMIC COMPANION
Earth has one moon.
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HOME, SWEET HOME
Earth is the perfect place for life as we know it.
Our atmosphere protects us from incoming meteoroids, most of which break up in our atmosphere before they can strike the surface.
Pop Culture
Storytellers explore the nature of our planet and possible alternate realities in many books, movies, and television shows. The iconic film "Planet of the Apes" (and its sequels) takes place in a future in which astronauts "discover" a planet inhabited by highly intelligent apes and primitive humans, only to realize later, much to their dismay, that – spoiler alert! – it was Earth all along.
In the long-running and re-booted television series "Battlestar Galactica" – tired survivors of a war with highly evolved robots called Cylons are on a quest to find Earth, a long-lost colony.
In other stories, Earth has been abandoned or destroyed, such as in the Joss Whedon series "Firefly," or the book and its film adaptation "The Hitchhiker's Guide to the Galaxy." In the animated feature "Titan A.E." – Earth has been destroyed by an alien species, but a well-placed planet builder recreates it and all the species that live on it.