You can define Earth in many ways, but above all else it is home. It’s not just home for us humans. It supports the life of millions of plant and animal species too.
While Earth may seem like the center of our universe, it's one of more than 1 million objects in the solar system. And technically the universe has no center.
We live on one of eight planets in a solar system so vast it's hard to fathom. Here's just one example: The sun is at the center of our solar system, and Earth, the third planet from the sun, is more than 93 million miles away from the sun. Neptune is the farthest planet from the sun. It is 2.78 billion miles from the sun.
Now back to Earth. Our home planet is about 71% water and 29% land, and all that land and water supports the many millions of plant and animal species that call it home.
We've just brushed the surface of what Earth is, so keep reading to learn even more.
It's really old, but it won't last forever
Earth formed more than 4.5 million years ago! It was formed as a result of gravity. Essentially, gravity pulled masses of swirling dust and gas together to form our home planet. Even though it has been spinning for billions of years, it will not last forever.
Words to know
Celestial: Relating to the sky.
Contract: To decrease in size, number or range.
Radiate: To emit in the form of rays or waves.
Tectonic: Relating to the structure of the Earth’s crust and the processes that take place within it.
Earth revolves around the sun, and the end of Earth's existence is linked to the sun. Eventually, the sun will run out of fuel. When that happens, the core of the sun will begin to contract. This will cause nuclear reactions. It will also cause extra heat produced deep within it to puff out and radiate toward other celestial bodies.
When this happens, the solar system's innermost planets — Mercury and Venus — will be swallowed up by the sun. Earth's fate is less certain because of its distance from the sun. Modeling suggests it will not survive the sun dying out as an intact planet. This may seem like a dire fate, but NASA predicts the sun still has about 5 billion to 6 billion years worth of fuel left.
While Earth may exist for billions more years, whether it can support human life is another matter. Since the mid-1800s, human activity has been causing Earth's climate to change, according to NASA. These changes are causing our oceans to get warmer, ice sheets to get smaller and sea levels to rise, among other effects. Climate change has also caused an increase in the frequency of extreme weather events. If Earth's climate continues to change, it will at some point make the planet unlivable for humans and other living things.
It isn't quite round
No one would blame you for thinking our home planet is a perfectly round sphere. However, in reality it isn't and never has been. Not quite anyway.
Earth bulges slightly at the Equator, but it's an ever-so-slight bulge caused because it rotates on an axis. Earth measures 7,926 miles when measured at the Equator but 7,900 miles when measured from the North Pole to the South Pole. If our planet was a perfect sphere, those two figures would be equal.
The 26-mile difference is slight in the grand scheme of things. Earth is only about 0.3% larger at the Equator than it is when measured from it poles, and the difference is too small to be perceptible when seen from space or in photographs.
Earth may be getting less round too. Recent research shows that Earth is getting wider at the Equator, and it is believed to be because the glaciers are melting. Another wild fact: Earth's shape is not constant. It's actually always changing. Some of these changes are regular and cyclical, such as those caused by daily tides. Earth's shape also changes as tectonic plates shift or after violent events such as earthquakes, meteor strikes and volcanic eruptions.
It has really high highs and really low lows
Northern Illinois and the Midwest are known for their flat landscape, but rugged, mountainous terrain covers many parts of our planet. The highest point on Earth is Mount Everest, which stretches more than 29,000 feet — or more than 5 miles — into the sky. It is in Nepal and Tibet and is part of the Himalayan mountain range. The highest point in the United States is Denali in Alaska. It is 20,310 feet tall.
The lowest point on Earth is the Dead Sea, which is located between Israel and Jordan. It sits 1,414 feet below sea level. In addition to being the lowest point on Earth, it is also one of the saltiest bodies of water on the planet. It is more than 9 times saltier than the ocean and too salty for many organisms to live in. The lowest point in the United States is Death Valley in California, which is 282 feet below sea level.
The lowest spot on the surface of the Earth is nothing compared to the deepest depths of the oceans. The deepest spot in the ocean is called Challenger Deep, and it is 35,876 feet deep. You could put Mount Everest in Challenger Deep and its peak would still be more than 1 mile below the water's surface. Another helpful comparison: You could stack 20 Willis Towers (formerly the Sears Tower) on top of one another and it still wouldn't be as tall as Challenger Deep is deep.
Challenger Deep is in the western Pacific Ocean at the southern end of the Mariana Trench. The closest landmass to the Mariana Trench and Challenger Deep is the U.S. territory of Guam, which is about 1,300 miles east of the Philippines and 2,900 miles north of Australia.
Earth's name is unique
With just one exception, all the planets in our solar system are named for ancient Greek and Roman gods. That one exception? Our home planet of Earth. The term Earth has been used for at least 1,000 years.
The term "earth" is derived from an Old English word pronounced "eorthe." That term is derived from the Anglo-Saxon word "berth." Other European languages that are related to English have similar words. In Dutch, they use the word "aarde." German speakers use the term "erde." The terms can refer to our planet or the ground itself.
It's squishy
The ground we stand on is solid, but Earth's interior is actually more squishy than solid. Have you learned that Earth is composed of three layers: the crust, or outer layer; the mantle, which is Earth's middle layer; and the core, or inner layer. The majority of Earth's volume — about 84% of it — is its mantle, which is 1,802 miles deep. The mantle is where the squishiness comes from.
Earth's mantle mostly consists of rock, but because of high pressure and high temperatures, it is in a semi-solid state rather than a solid state. Because it is not solid, the matter in the mantle can flow rather than stay in place. This movement is what leads to earthquakes, volcanic activity and shifts in the Earth’s tectonic plates.
Earth's crust is solid because of activity in the mantle. The crust is only the outer 1% of Earth, and it formed over millions of years. Essentially, eruptions of lava and water-containing minerals caused the outer layer of the mantle to become solid. That solid layer is what is today Earth's crust.
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