We're lucky to live on such an incredibly perfect planet, where the air is exactly the mix of chemicals we need, there's lots of water, and the temperature is just right — at least in some places some of the time. Of course, in reality we're here because of all those circumstances that foster life as we know it. Here are 13 of the most fortunate circumstances of our world:
1. Third Rock: There's a reason we've found life on Earth and nowhere else. Our world orbits the sun at just the right distance — not too hot, not too cold. This habitable zone is where water can exist in liquid form — a basic requirement for life. Nobody is bragging about their oceanfront property on Mars or the cool breeze on Venus.
2. The Moon: But be thankful for our great big beautiful satellite. Without the moon, you might not be here. Its gravitational tug creates tides (with the help of the sun), and one theory holds that life originated in tidal regions. Another suggests tides may have set up conditions for sea creatures to transition and become the first land animals. [Top 10 Amazing Moon Facts]
3. Stable Rotation: Earth's rotation brings the sun up each morning and, thankfully, puts it back down. If it weren't for this, one side of the world would be unbearably scorched and the other would freeze life to death. So you know, the moon is stealing some of Earth's rotational energy, slowing us down by about 1.5 milliseconds every century. If you can hang around for about 140 million years, you'll finally get that extra hour in the day you've been wishing for.
4. Constant Gravity: Nobody expects gravity to go anywhere anytime soon, but it's interesting to note that scientists don't really understand how gravity works. We take it for granted, but gravity helps make us who we are. It defines our strength, contributes to the shape and form of every living thing. An average male human transported to Mars could dunk on a 26-foot-tall basketball hoop (due to the reduced gravity that presumably gives aliens those long necks). A 200-pound man trying to stand on Jupiter (good luck) would weigh 480 pounds and would have to get a lot stronger just to jump more then a few inches. [6 Weird Facts About Gravity]
5. Protective Magnetic Field: If Earth did not have a strong and relatively stable magnetic field, we'd all be fried by cosmic rays and solar storms. That said, the field, which emanates from the poles and encircles the planet, is not actually all that stable. Since the early 1800s, the magnetic north pole has crept northward by more than 600 miles (1,100 kilometers). The pace has picked up to about 40 miles (64 km) per year lately, roughly double the pace a century ago. About every 300,000 years or so the magnetic poles flip, a process that takes thousands of years. Scientists say we're overdue for another flip, which means your distant future descendants will need to buy new compasses.
6. Temperate Zones: Some life has adapted to the most frigid places on Earth (including Antarctica, where the planet's record low was set at minus 128.6 degrees Fahrenheit, or minus 89.2 degrees Celsius) and its hottest deserts (including El Azizia, Libya, where the record high of 136 degrees F, 57.8 degrees C, was recorded). But life achieves greatest diversity in more temperate climes, namely the tropics, where moderation rules. [North vs. South Poles: 10 Wild Differences]
7. The Deep Blue Sea: About 70 percent of our world is covered by oceans. The significance can't be overstated: Abundant liquid water is the most significant distinguishing factor on this planet that supports life.
8. Sea Level: Oceans can be a blessing and a curse. Until recent decades, the idea of "sea level" was a stable concept. That was fortunate for people building beach houses. But the situation is changing. Melting ice caps and glaciers, along with warmer seas, are causing ocean levels to rise. Some islands are in the process of going under, and coastal regions everywhere may be affected. Along the U.S. Eastern Seaboard, sea level has risen 0.08 inches (2 millimeters) per year from 1950 to 2009.
9. Green, Not Purple: We take green for granted, but green is an important color. It is nature's sign that sunlight, carbon dioxide and water are being converted into plant food by photosynthesis — the process that provides the basis for animal life. Early in the planet's history, life may have been purple, one theory goes, assuming microbes used some molecule other than chlorophyll. Who knows if purple would have tasted good!
10. Electric Earth: Dozens of U.S. residents are killed by lightning every year. But lightning may be a key to the origin of life. With water, methane and other chemicals in the atmosphere, lightning can create amino acids and sugars that are building blocks of life. The well-known Miller-Urey experiment in 1953 raised the possibility that lightning may have been a key to the origin of life.
11. Major Recycling Effort: Some worlds are pretty static, even dead from a geological perspective. They lack the internal movement we call plate tectonics. Earth, on the other hand, is constantly changing, recycling its crust into the mantle and bringing the superheated material from below back to the surface. Yes, that generates deadly earthquakes and killer volcanoes. But one theory on the origin of life holds that it began around deep-sea volcanic vents, where there was heat and lots of interesting minerals oozing forth. Recycling on this huge scale may thus be a key to life.
12. Space: Earth doesn't exist in a vacuum. The space in our solar system is dotted with asteroids and comets, plus dust and traces of gas. Even now, small space rocks rain down on Earth daily. Big ones slam into the planet often enough to keep NASA on constant lookout. And in the early years of the planet's formation, giant collisions with comets and asteroids brought water and other important chemicals to the planet, making the origin of life possible. [Top 10 Ways to Destroy Earth]
13. Staying Power: Earth was formed about 4.54 billion years ago. It took hundreds of millions of years before simple life forms appeared. However, it wasn't until very recently — around 585 million years ago — that any advanced multicellular animal life developed, and these were just tiny sluglike creatures the size of a pill. Humans have walked the surface of Earth for an eye-blink of geologic time — perhaps 4 million years. If our star and our world had shorter life spans — as many do — we'd never have gotten on our own two feet and developed brains big enough to ponder just how lucky we are to be here.