THE MAKINGS OF A TRULY
A Rock, A River, A Tree
Hosts to species long since departed
Marked the mastodon,
The dinosaur, who left dry tokens
Of their sojourn here
On our planet floor,
Any broad alarm of their hastening doom
Is lost in the gloom of dust and ages.
—Maya Angelou, from “On the Pulse of the Morning”
You’ve probably heard this one: The reason our planet is so great for life is the extreme good fortune of our location in the solar system. If Earth moved just a mile closer to the Sun, we would all burn up, and if it moved just a mile farther away, the oceans would freeze. I’ve heard this claim from so many people—students, school teachers, friends, and even preachers—that it’s apparently attained the status of an urban legend.
It sounds pretty good, and like most urban legends it contains a kernel of truth: There must indeed be some distance from the Sun that would be too hot for life to survive on Earth, and some distance at which it would be too cold. But the distance isn’t a mile, nor even a few million miles, as you can realize just by thinking about Earth’s orbit around the Sun: Earth’s orbit is not a perfect circle, but rather is an ellipse (oval) in which our distance from the Sun varies from a minimum of about 91 million miles each January to a maximum of about 94 million miles each July. Thus, according to the urban legend, our whole planet would burn up each January and freeze each July. In reality, this 3-million-mile variation in distance has virtually no effect on the weather at all, a fact that becomes obvious when you remember that the northern hemisphere has