Our solar system emerged out of such fiery transformation. Five billion years ago a shimmering cloud created by supernova explosions began its gravitational collapse into a thousand new star systems. Throughout this vast cloud, new centers of attraction appeared with an infant star, like a jewel shining at the heart of each center. One of these centers became our Sun with its eight planets—a solar system. This vast ocean of our solar system is like a womb that eventually brings forth life.
How did this happen?
In the beginning our infant Sun was completely surrounded by hydrogen, carbon, silicon, and other elements disbursed by the supernova explosions. As they drifted through space these elements would brush against each other and begin to cohere into tiny balls of dust. Over millions of years these “planetesimals” continued accreting and growing until they were the size of boulders and then as large as mountains. Not all collisions resulted in larger bodies. Many were so violent that they tore both bodies apart. But over millions of years these planetesimals continued to absorb all the loose matter circling about. Our solar system, with its eight planets, its band of asteroids, and its one infant sun, slowly came into being.
It is remarkable to realize that over immense spans of time stellar dust became planets. In the earliest time of the universe this stellar dust did not even exist because the elements had not yet been formed by the stars. Yet hidden in this cosmic dust was the immense potentiality for bringing forth mountains and rivers, oyster shells and blue butterflies.
Such a process occurs over and over again in the unfolding of the universe: the self-assembling powers of the universe create new structures that allow new forms of creativity to emerge.
The long process from stellar dust to planets is filled with violence and chaos and yet gives rise to new portals of creativity. Even though this birthing took place billions of years ago, there are reminders of that original process. When at night we see a shooting star, that meteoric path of light streaking across the sky, we are witnessing one of the original pebbles of the early solar system finally coming to rest after four and a half billion years of circling the Sun alone.
Earlier peoples could only speculate about the formation of the planets and the Sun and the Moon. Yet in looking up at the night sky they had a sense that they were living amidst an ocean of energy swirling with stars and planets. They sought to orient themselves in this vast ocean by naming the planets and seeing living forms in the constellations of the stars. The deep drive to participate in the universe led to the creation of stories and myths—the planets were persons, the stars were kin, the Sun was a god.
In cultures around the world, this urge for participation gave rise to numerous efforts to map the movements of the heavens. To align with the planets was a means of grounding humans in the immensity of the cosmos. The rhythms of time and space were clarified—the calendar was established, seasonal rituals were determined, the cycles of agriculture were defined. Human life could thus be navigated by the planets and the stars—on land or on sea.
We too are seeking our path into the universe as we discover more about the planets—their movement and their composition. It was difficult for us humans to realize that we are living on a planet traveling around a star. One of the great moments of modern science was Kepler’s discovery that planets moved not in circles but in elliptical orbits. This became a final step in the remarkable revelation, begun by Copernicus, that the planets moved not around the Earth but around the Sun. We are still absorbing the stunning realization that we are living in a vast solar system centered on a massive star.
It was only in the twentieth century that we discovered what planets are made of and how they were formed. There are two basic kinds of planets—larger planets that are gaseous and smaller planets that are rocky. In our solar system, Jupiter, Saturn, Neptune, and Uranus are the large planets. They have enough gravity to hold onto the lightest elements and thus they remain in the form of a gas. But they do not have enough gravitational strength to press the elements together into fusion processes that would enable them to become stars. As a result they remain gaseous, balanced between the realms of the rocky planets and the burning stars.
The smaller planets are Mercury, Venus, Earth, and Mars. When they first formed they were largely molten rock, but slowly, over hundreds of millions of years, these planets cooled. Eventually, Mercury and Mars solidified and became rigid all the way to their centers. But Earth—and possibly Venus—remained in a partially molten state. This special condition was the start of a new adventure in our solar system.
Earth’s story is one of a planet finding a way to remain in the creative zone between the chaos of roiling gas and the rigidity of solid rock. When Earth was still in a partially molten state, gravity drew the heaviest metals, such as iron and nickel, thousands of miles into the core. These accumulated until eventually this dense iron core extended halfway up to the surface. Piling up on top of the core came matter such as iron-rich silicates and magnesium, components of the denser rocks. These iron-bearing magnesium silicates formed the middle area of the Earth, the mantle. Lastly, Earth’s crust formed around the mantle. Only ten to one hundred miles thick, the crust is composed of light felsic rock, like granite, surrounded by large areas of ocean crust, formed largely of basaltic rocks, crystallized from upwelling magma. We can imagine Earth as an egg. Its inner core is like the yolk, its mantle is like the egg white, and its crust is like the shell.
This same process occurred on Mars, but it froze in this state. The amazing thing about Earth is that it did not freeze. A seething disequilibrium continued. The intense gravitational pressure and the heat generated by radioactive decay within the Earth produced a flow of magma as large as Earth itself. The heat gave rise to plumes of matter that floated to the surface and broke through as lava. As it cooled and solidified, the matter began its descent back into the center of the planet. This dynamic recycling of elements has, for billions of years now, operated as a process of renewal on a planetary scale.
The great convection cycle of rising and falling matter is what moves the crust over the surface of the planet. That the continents fit together like a jigsaw puzzle was first noticed by sixteenth century explorers, such as Ferdinand Magellan, who could draw upon their circumambulatory voyages to sketch maps of the entire planet. But it was not until 1915 that one scientist, Alfred Wegener, took the next step and hypothesized that the reason the continents fit together geometrically was because they were actually in motion and had once been parts of a single, connected land mass. Following his surmise, scientists over the next half century assembled the theoretical models and empirical data necessary to show that, indeed, the Earth’s crust was in motion.
The understanding provided by this theory of plate tectonics must be considered one of the most significant in history, the geological equivalent to Charles Darwin’s discovery of natural selection and the Einstein-Hubble discovery of an expanding universe. For just as the work of Einstein and Hubble enables us to hold the dynamics of the entire universe in mind, and Darwin’s theory enables us to conceive of life as a single, complex narrative, so too the theory of plate tectonics illuminates for us the ways in which Earth developed its geological and topographic features over the past four billion years.
Earth has continuously woven itself into new combinations out of the seething movements of Earth’s plates. The plates would collide with one another and be forced back down to be melted and recycled in the mantle. Precisely because Earth lived in the zone between chaos and rigidity, its matter churned and crystallized into several thousand new minerals and a vast number of polymers. Many of these polymers existed nowhere else in the solar system and provided a precious portal for Earth’s creativity. But that creativity also depended in particular ways on Earth’s dynamic relationship with its offspring, the Moon.
Just as a shooting star on a summer night can thrill us with its display of radiance, so too does the Moon enchant us. We feel the rhythm of its waxing and waning; we are fascinated by its luminous light; we are stunned by a lunar eclipse. We sense its mysterious effect on us like its gravitational pull on the changing ocean tides. A full Moon brings forth a flood of romance; a new Moon awakens promise and possibility.
Just as the rhythm of the Moon is embedded in the tides and in the months of our calendars, the mythic power of the Moon is celebrated in story and song. The Moon is the source of hundreds of myths ranging from the Man in the Moon for Europeans and Americans to the Rabbit in the Moon for the Chinese and Japanese.
Because of this power of attraction we have wondered, “Where does the Moon come from?” This has only recently been clarified by scientists. The Moon’s origin took place at the beginning of our solar system, four and a half billion years ago. As we described earlier, this was a time when the matter left over from the Sun’s birth was accumulating into ever larger spheres, the planetesimals. The process giving rise to our Moon began when a large planetesimal the size of Mars collided with Earth, plowing right through the surface in the most violent encounter Earth has ever experienced. Some of the colliding planetesimal was absorbed into Earth. As Earth was largely molten, it quickly resumed its spherical shape.
But huge portions of both Earth and the colliding planetesimal were blasted out into space and formed a ring of lava around the Earth. The Moon and Earth, liquefied into magma by the collision, now separated and cooled. In a process similar to the formation of the planets, the Moon eventually stabilized. Because it was smaller, it froze into a fixed terrain of rugged highlands and smooth lowlands after one billion years.
Originally the Moon was closer to Earth. Earth was rotating more quickly and thus each day was only five hours long. Over some four billion years the Moon has been spiraling gradually outward away from Earth. As we view the Moon in the night sky we see it now as an ancient offspring of Earth, radiant with light reflected from the Sun, floating through an ocean of shimmering darkness.
If the Moon holds the mystery of night, the Sun empowers the day. Like the Moon, the Sun has an enormous effect on us—we seek its light for warmth and comfort. When we are deprived of it—especially in long winter months—we can become melancholic or anxious. The Sun literally lights us up.
For many cultures the Sun was considered a god—Ra in Egypt, Amaterasu in Japan. Great structures, such as those at Stonehenge in England and at Chaco Canyon in North America, were designed to observe the movements of the Sun. In modern times Claude Monet and other impressionist painters sought to capture the shimmering dance of light. The return of the Sun’s light at the winter solstice and its diminishment at the summer equinox are still marked by festivities around the world.
But what is the source of the Sun’s power, and how does it affect the planet? This massive burning star releases its energy in every direction, freely bestowing its light on our world. At ninety-three million miles away, we on Earth receive only the tiniest sliver of this energy. Yet all life on Earth depends upon this sliver.
In pondering the source of the Sun’s power we can now reflect on something no earlier people could know. This knowledge became available in 1905, when Einstein discovered the equivalence of mass and energy. We now know that the Sun is converting four million tons of its mass into energy every second. In its core, the element hydrogen is being transformed into helium, releasing light in the process. The Sun is transforming its very essence into light. With each passing instant, more of its mass is becoming energy.
How riveting to discover that this transformative process at the center of our solar system brought forth life on our planet. Without the Sun, photosynthesis and green plants would not have blossomed forth, and other forms of life would not have evolved. Life is dependent on the roaring energy of the Sun—light becomes nourishment for the entire Earth community. This is the heart of transformational processes that pervade the universe. We see it in the vast explosion of the supernova; we observe it in minute chemical transformations. It is what the Chinese call the fiery furnace of the cosmos.1
The fiery furnace of the universe displayed itself also in the early formation of Earth. Like soup in a huge cauldron, Earth cooked and cooled over millions of years. Volcanic processes released molten lava as well as huge clouds of dust particles and water vapor into the atmosphere. Earth was struck by large and small planetesimals, which brought more water and other compounds into the roiling mix.
The temperature of this early atmosphere was so hot that the rains turned to steam and dispersed as water vapor far above the ground. When the water eventually could reach the surface of the Earth, it formed lakes and ponds, but these quickly boiled back into steam. Earth was a fiery cauldron, in which its elements moved freely and quickly between solid, liquid, and gaseous states. This was a time of wild, frenzied activity—volcanoes rising up from the bottom of the oceans and boiling with lava, huge waves churned up by the tidal force of the nearby Moon. The oceans were a deep brown color; the sky was a pinkish-orange from an atmosphere rich in hydrogen sulfide.
As Earth continued to cool, the steam that rained down for millions of years eventually covered the surface of Earth with an ocean of water. But then a giant asteroid would once again smash through the ocean and the fragile crust, heating up the planet so that the rock melted into liquid and the ocean water boiled back into steam. Water was constantly transforming and being transformed.
Dust from asteroid impacts as well as from volcanic explosions blocked out the Sun. Night covered the Earth for millennia, until massive torrents of rain brought the dust back to Earth and a new ocean formed.
After millions of years, more stable conditions emerged for rock, water, and air. Earth became encircled by great tidal oceans and was held by a thin layer of atmosphere. Within such a double embrace of oceans and atmosphere, Earth brought forth a new marvel—the living cell.