It’s probably best if we don’t think too much about Earth. After all, it’s a tiny orb spinning more than 1000 mph at the equator while simultaneously zipping through space at 67,000 mph. It circles a mysterious, 10,000°F sun that’s more than 100 times its size, and spends most of its orbit narrowly (in a cosmic sense) avoiding collisions with giant chunks of rock that could practically wipe its surface clean. But if you’re feeling brave, here are a few things you might not know about Earth.
1. Earth is about 93 million miles away from the sun.
As you probably know, at this distance, it takes one year for Earth to complete one revolution of its orbit, and 24 hours to complete one rotation on its axis. The surface of Earth has temperatures ranging from -126°F to 136°F. The planet is about 7900 miles in diameter (though the deepest we've ever drilled is 7.6 miles). There are roughly 332.5 cubic miles of water on the planet, which is enough that, if the water broke away from Earth and organized itself into a sphere, it would have a diameter of 860 miles—about 40 percent that of the moon.
2. The first photograph of Earth from space was taken in 1946.
It’s a grainy, black-and-white shot of a tiny slice of our world, curved with the ink of space as a backdrop. In 1960, weather satellites began sending photographs back to Earth, images that were still hideously deformed but scientifically valuable, especially for meteorologists, who now had stunning views of cloud systems from which to work. NASA’s ATS-III satellite in 1967 returned the first color images of Earth in its entirety. At last, we could see our living world, ringed in space and wrapped in billowing clouds.
On Christmas Eve, 1968, Apollo 8 astronaut William Anders sent back Earthrise, a now-iconic photograph of a fragile cerulean orb rising over the lunar surface. But the most famous photograph of the Earth, by far, was taken about four years later, on December 7, 1972: the Blue Marble. You’ve probably seen it countless times, but you may be less familiar with how astronaut Harrison Schmitt described the sight to Mission Control: “I’ll tell you, if there ever was a fragile-appearing piece of blue in space, it’s the Earth right now.”
3. Earth has a natural satellite.
Earth is the first planet, moving outward from the sun, that possesses a moon. We call our moon “the moon” (which will be a real headache centuries from now, when we’ve colonized the solar system). Every 27.32 days, the moon completes an orbit of Earth, which is why it has phases. When Earth is between the sun and the moon, we see the moon in full illumination (a round orb). As it circles Earth, less and less of its visible surface is illuminated, until at last the moon is between the sun and Earth. At that point, the “far side” of the moon is in full illumination, and from our perspective, the moon is receiving no light at all. The cycle then repeats itself, with more of its disc being illuminated as the month elapses, until it is again full. Because the length of the moon’s orbit is just shy of a month, every so often a month (which derives from the word moon) has two full moons, the second of which is called a blue moon.
The moon does spin, but in synchronous rotation with Earth. In other words, it spins at the same speed as its orbit. As a result, Earth gets to see only one side of our only natural satellite. The best guess for the origin of the moon involves an object the size of Mars smashing into Earth 4.5 billion years ago, sending debris into space. This debris organized itself into a molten form of the alabaster orb we know and love. Within 100 million years, an early crust had begun to form. Today, the moon influences the tides of the ocean and eases our axial wobble, keeping things (more or less) nice and stable—a perfect condition for life.
4. Earth is the only body in the universe known to harbor life.
When it comes to life, there are a lot of maybes in the solar system. Maybe Mars supported life billions of years ago. Maybe Jupiter's moon Europa is teeming with life today. The problem is that there is no evidence anywhere of anything that wiggles, walks, or swims … except on Earth. And it has been tough going.
Four billion years ago, Earth’s surface was sterilized during the Late Heavy Bombardment, when asteroids pummeled the inner solar system. To get some idea of what things must have been like during the LHB, look at the moon. Most of its craters were formed during that time. Life survived on Earth in large part thanks to the hydrothermal vents at the bottom of the ocean.
There have been five mass extinctions on Earth, the worst of which (the Permian-Triassic, or “P-T Event”) was 250 million years ago, wiping out 96 percent of marine species and nearly three-quarters of land vertebrates. Sixty-six million years ago, the Chicxulub impact wiped out 75 percent of all life and ended the reign of the dinosaurs. Things recovered nicely, though, and today, biologists think there could be 8.7 million species of life on Earth. That’s not bad considering the universe’s apparent hostility to life, and makes what we have going here all the more special and worth preserving. And we’d better get on it: Many scientists argue that we’re in the midst of a sixth mass extinction—and we can only partially blame it on cats.
5. Climate change is threatening life on Earth.
“Global warming is real, it’s caused by people, and it’s a big problem,” Willis told Mental Floss in 2017. “Every year the impacts of human-caused climate change get bigger and bigger, and are felt more and more across the planet.” We feel the effects of climate change today, but the worst is yet to come in terms of economic and social disruption: “Right now we have a choice about what kind of planet we want to have in the future. And the choice is: Do we want to continue to burn fossil fuels and heat up Earth, or do we want to try and stabilize our climate and keep it more or less like we’ve had it for the last 10,000 years?”
6. Earth is the only planet with stable water at its surface.
Icy moons like Europa and Enceladus have subsurface oceans of liquid water, and Titan, in addition to a possible subsurface water ocean, has vast lakes of liquid methane covering its surface—but no other celestial object has oceans of H2O like ours.
Unfortunately, they're rising. NASA's Jason-3 spacecraft measures the height of the ocean with 1-inch accuracy. Every 10 days, it collects data on the entire ocean, revealing details about such things as ocean currents and how they change, tilts in the ocean's surface, and the average volume of the ocean. “The oceans are growing for two reasons,” Willis said. “One is because they absorb heat trapped by the greenhouse gases, and the other is that the ice in places like Greenland and Antarctica and tiny glaciers all across the planet are all melting and adding extra water to the oceans. This satellite measures these things combined, and in a way it’s really taking the pulse of our planet.”
A decade ago, the ice sheets in Greenland and Antarctica were thought of as stable. They are the last remaining ice sheets that cover huge land masses, and today they are disappearing. In 50 years, their melting will be the dominant source of global sea level rise. "Every time a big discovery is made," says Willis, "it seems like the picture is worse than we thought it was. The possibility for really rapid ice loss and rapid sea level rise is greater than we thought."
7. In some ways, Earth's oceans are harder to study than other planets.
The oceans remain a giant unknown for scientists. Knowing more about them would answer many of our questions about life and the life of Earth. “Two-thirds of the planet is covered with water, and you can’t see through it. And you can’t shoot microwaves through it, and radio waves, and all the other kinds of things that we use even to measure other planets,” Willis said. “If you probe the ocean, there are still a lot of big mysteries down there.”
To understand how oceans really work would explain, for example, where the heat from global warming is going. Though the oceans absorb 95 percent of the heat trapped by greenhouse gases, it’s still a mystery where that heat energy actually goes. Similar questions exist as to how the oceans interact with ice sheets.
8. It isn't too late to take action for Earth's future.
But it will take a concerted effort to change our behavior—before it’s too late. “We think of global warming as something that happens in our cities, and it is happening there, but really 95 percent of the heat that’s being trapped is going in the oceans. And I don’t think people realize that. It just seems like, well, we’re getting the brunt of global warming here in Los Angeles—but that’s not true, really. It’s the sea life and the oceans that are getting the brunt of the change,” Willis said.
“One thing we should keep in mind is that all hope is not lost,” he continued. “We are beginning to see changes in our economy, we’re beginning to see the growth of renewable energy, and the strong desire to move to a fuel source that doesn't cook us, and I think that’s a good thing.”
A version of this story was published in 2017; it has been updated for 2023.