Estimates vary from 2 million to 100 million. No one knows how many species there are on earth. Without its tailor-made moon, our planet would wobble like a spinning top, perhaps even tipping right over and turning on its side, as it were! The resulting climatic, tidal, and other changes would be catastrophic. The moon also contributes to the planet’s stable spin axis. Mere coincidence? It seems unlikely.įor one thing, the moon is the principal cause of ocean tides, which play a vital role in earth’s ecology. Thus, when compared with other moons in our solar system, our moon is unusually large in relation to its host planet. Its diameter measures just over a quarter of that of the earth. The perfect “neighbor”: If you had to choose a “next-door neighbor” for the earth, you could not improve on the moon. For good reason, it has been called “a very special star.” 2 The sun, meanwhile, is the perfect “powerhouse.” It is stable, it is the ideal size, and it emits just the right amount of energy. Moreover, earth’s path is almost circular, keeping us roughly the same distance from the sun year-round. The ideal “street”: No less “prime” is earth’s “street,” or orbit within our solar system “city.” About 93 million miles (150 million km) from the sun, this orbit lies within a limited zone that is habitable because life neither freezes nor fries. “We live in prime real estate,” says Scientific American magazine. Farther out, those elements are too scarce farther in, the neighborhood is too dangerous because of the greater abundance of potentially lethal radiation and other factors. This “habitable zone,” as scientists call it, contains just the right concentrations of the chemical elements needed to support life. To begin with, our “city,” or solar system, is located in the ideal region of the Milky Way galaxy-not too close to the center and not too far from it. By way of comparison, let’s call the Milky Way galaxy earth’s “country,” the solar system-that is, the sun and its planets-earth’s “city,” and earth’s orbit within the solar system earth’s “street.” Thanks to advances in astronomy and physics, scientists have gained deep insights into the merits of our special spot in the universe. When you write down your address, what do you include? You might put in your country, city, and street. Could the earth be located in a better position to host life?
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