Sizing Up the Earth

San Francisco Bay perspective. Created with Google Earth.

San Francisco Bay perspective. Created with Google Earth.
San Francisco Bay perspective. Created with Google Earth.

What has a mass of about 6 yottakilograms, occupies a volume of space of about 1 million million cubic-kilometers, is about 40 kilometers fatter than it is tall, and you could walk around it in about one year? Guesses, anyone? Did I mention it's open for business day and night. Still wondering?

If you guessed the planet Venus, close! Very close. It's actually good ol' Earth I've been thinking about lately, as a planet and home. These days, it's quite easy to think of our home world as shrinking, made smaller and smaller every day by modern transportation, telecommunications technology and our unprecedented propensity to make use of them.

My own daughter, long ago when she was an 8-year-old, made an observation on the size and scale of the Earth as we stood atop the Oakland Hills looking down upon most of the San Francisco Bay. "I can see the Bay," she said, pointing downward, "and an astronaut in space can see it, too." The scale of our small planet struck me at that moment in a different way than usual, for she was right. Here was a geographic feature that I could not only see in one sweeping gaze, but I could hop in my car and go visit any point on that feature in under an hour (traffic willing). And, yes, someone way out in space, seeing the Earth in its demi-entirety (‘cause you can only see half a planet at a time) could see it, too, as a major feature on the globe.

From this modern tiny-planet perspective, it's amazing to think of times when much of the planet was unknown to any one group of humans. What is a 5-hour plane ride today, between Europe and the East Coast of the U.S., was a big dark unknown only a few hundred years ago.

But, it doesn't take much to get back a perspective of Earth as a very, very large place. All you have to do is scratch below the surface we dwell on.


And while a journey to the center of the Earth places a linear perspective on it size (Jules Verne's very athletic explorers would have had to climb downward nearly 4000 miles!), it's the volume of our orb that packs a wallop of magnitude.

The entire world that we have direct experience with is the thinnest of onion layers, right here at the surface. All of those mountains, plains, vast desert expanses and forested wilds; all of that watery ocean surface and its great dark depths; all of that air-filled sky that comes right down to the ground and seems to stretch upward forever—all of that is thinner than a layer of tissue paper wrapped around a beachball. Think about the unexplored subterranean territory, even just the part close to the surface in Earth's crust! Think of all the gold down there, maybe forever beyond our reach. (You have to imagine there's far more gold inside the Earth than the dusting we've scraped off the surface, after all.)

In terms of volume, if you measure the space of the universe that we humans (and all life on Earth) live in as extending from the Earth's surface to the top of the troposphere (about 10 kilometers up), the interior of the Earth encompasses over 400 times as much space—and, to our knowledge, all of that is filled with rock and metal, mostly iron, oxygen, silicon, and magnesium.

Why, there's enough iron in our planet (about 2 yottakilograms of it) to build -- oh, about 2 million billion Golden Gate Bridges.

Earth may seem kind of small and cramped at times, but take heart in the fact that, in our Solar System, it's the largest "there" there is, after the Sun and gas giants.