From our position on the ground, just outside our home, we can see only a small fraction of our planet. Suppose we can levitate, and we’ll see far more. As we rise through the atmosphere, the air molecules spread out. Gravity is pulling them downward, and it can only hold a very thin layer to the Earth’s surface. As we rise past the top of the largest thunderstorm, approximately 12 miles up, 90 percent of the molecules in the atmosphere are beneath us. The deepest point in the ocean is 7 miles below sea level, and below that, there is dense rock for about 4,000 miles before you get to the center. Without a rocket, we humans are confined to a vertical range of a measly 18 miles, playing on the edge of the giant planet we call home. A layer of paint coating a ping-pong ball has the same thickness relative to the sphere it covers.
At a height of 62 miles, we are officially at the boundary between Earth and outer space, and we can see the globe rolling past beneath us—green, brown, white, and blue, spinning in the blackness of space. From up here, the scale of the ocean is shocking: a planet-sized shell made of one simple molecule repeated over and over again. Water is the canvas for life, but only in the Goldilocks zone,* the energy range within which the molecules move about as a liquid. Give those molecules extra energy, and their vibrations will shake apart any complex molecules that they house. More energy still, and they will float away as a gas, useless for protecting fragile life. At the lower end of the Goldilocks range, as you reduce the energy, the vibrations slow until the molecules must slot themselves into an ice lattice. Immobility like that is the enemy of life. Even the process of building these inflexible ice crystals can burst any living cell that contains them. Our planet is special not just because it has water, but because that water is mostly liquid. From our vantage point here on the edge of space, Earth’s most precious asset dominates the view.
Perhaps, down there, as the Pacific Ocean glides past, a blue whale is making sound waves, calling into the gloom. If we could watch that sound traveling beneath the ocean surface, we would see it traveling outward like ripples on a pond, taking an hour to reach California from Hawaii. But the sound is hidden in the water, and no evidence of it is visible from up here. The oceans are filled with sound, overlapping pressure oscillations pulsating outward from breaking waves, ships, and dolphins. The deep rumblings of Antarctic ice can travel underwater for thousands of miles. From our viewpoint on the edge of space, you would never know that any of it was there.
Everything on the planet is spinning, traveling once around the Earth’s axis every day. As winds travel across the spinning surface, they tend to keep going in a straight line, although friction with the ground and confinement by the air around them constrains their path. From up here, we can see that the winds in the northern hemisphere tend to turn to the right, relative to the ground, as they carry on in spite of the spin of the Earth. So weather, especially the weather farther away from the equator, spins. Hurricanes rotate, and so do the smaller storms that we can see rolling across the oceans. The eye of the storm is the hub of each wheel, and each wheel must spin because the Earth spins.
Over Antarctica, thick snow clouds are gathering. Inside each one, billions of individual water molecules exist as a gas, jiggling around with the oxygen and nitrogen. But as the cloud cools, they are giving up their energy and slowing down. When the most sluggish molecules bump into a nascent ice crystal, they lock on, each in a fixed place in the ice lattice. As the snowflake is buffeted up and down inside the cloud, the molecules on all six sides of the original crystal find themselves in the same conditions, and stick in the same way. Molecule by molecule, a symmetrical snow crystal is built. After hours of slow growth, the crystal is large enough for gravity to win the battle and it tumbles from the bottom of the cloud. Below is the Antarctic ice sheet, the largest agglomeration of ice on Earth, stretching sideways for thousands of miles and down for thicknesses of up to 3 miles. The accumulation of ice is so heavy that the continent itself has been pressed downward under the additional weight. But every molecule of that white expanse fell in a snowflake, and the pile of snowflakes has been growing for a long time. Some of the water here has been frozen for a million years. In that time, the molecules have vibrated about their fixed crystal lattice location continuously, but never fast enough to become a liquid again. In contrast, the molecules being pushed out of Hawaii’s volcanoes as lava are only just dropping below 1,100°F for the first time since the Earth was formed, 4.5 billion years ago.