Earth is a special spot in the solar system for so many reasons—its sprawling continents, its blue seas, its New York-style pizza. But one Earthly thing stands out above the rest: its earthlings. Ours is the only planet known to harbor life. In fact, Earth’s unique combination of air, water, and land nurtures life of every sort, from microscopic amoebas to submarine-size blue whales to you, an intelligent life form contemplating the clockwork of the solar system.
Earth’s veil of atmosphere not only provides the right mix of breathable air for animals and plants, it also acts as a sort of force field against solar radiation and deadly space debris. As much as 22,000,000 pounds (10,000,000 kilograms) of meteors burn harmlessly in the Earth’s atmosphere each day. The solar system’s other planets are typically too hot or too cold to support liquid water, but Earth is just right. Life began more than 3.5 billion years ago in our oceans, which cover nearly 70 percent of the planet’s surface and are a source of the water vapor responsible for our weather. And before you get eager to blast off and explore the rest of the solar system, consider this: Scientists know more about the surface of the moon than they do the depths of the oceans. Our world still holds plenty of mysteries for the solar-system explorer.