The Universe Within (6 page)

E
ver since the big bang, innumerable stars and galaxies have emerged and disappeared. We are relative newcomers to this party. By “we” I mean our entire
solar system.

It took big ideas and big science to see how our little patch of the universe came into being. The Swedish thinker
Emanuel Swedenborg was occupied by important questions throughout his life. Born in 1688, he lived most of his eight decades believing he should have one great idea per day. In his early years, he worked as a natural philosopher seeking to intuit the structure of the natural world. He inferred, for example, the presence of nerves and a nervous system. Turning his thoughts to the cosmos, Swedenborg proposed a theory for the origin of the solar
system. He envisioned that the sun developed from a cloud of gas and dust that collapsed on itself and condensed. As the sun took shape, the primordial dust remained as a disk of debris that swirled around the young star. Over time, portions of this cloud coalesced to form the planets of the
solar system. The idea was to remain dormant until two decades later, in 1755, when the philosopher
Immanuel Kant had his go at developing ideas on the origin of the solar system. The theory he ultimately developed was largely similar to Swedenborg’s.

Pierre-Simon Laplace (1749–1827) was one of the greatest mathematicians of all time, called by some the French Newton. Laplace’s name peppers the fields of mathematics and statistics. There are, for example, the Laplace equation, the Laplacian operator, and the Laplace transform, tools to understand electricity, magnetism, and the motion of bodies in space. His real passion was to uncover the order in the heavens, the shape of the planets and the orbits of celestial bodies. With this intellectual goal, he converted the philosophical ideas of Swedenborg and Kant to the precise language of mathematics.

If a dust cloud in space gets to the right size, Laplace conjectured, particles inside will interact such that gravity will pull them together as other forces act to separate them. This push-pull means that a relatively amorphous cloud of dust can, under conditions where the pull wins out, develop into a swirling disk of debris. Over time, the gravitational attraction of the particles of dust in the disk break it into separate concentric rings—imagine a striped Frisbee. If the mass of dust in the rings is large enough, the particles could then condense to form the various planets of the solar system. These big events would happen not overnight but over timescales of millions of years.

Laplace’s mathematical reformulation of Swedenborg’s and Kant’s ideas served as midwife for their transformation from interesting concepts to testable predictions. But the problem was that the technology to make the necessary measurements did
not exist in the late eighteenth and early nineteenth centuries. Consequently, our understanding of the formation of the solar system stagnated for over a hundred years.

Enter big science. In 1983, scientists from the Netherlands, Britain, and the United States developed a
satellite that could
map the stars from an orbit around Earth. This predecessor to the
Hubble Space Telescope was designed to perform one kind of observation really well: measure the
infrared spectrum of the entire sky to assess how much
heat is emanating from different stars. Through the course of their lives, stars emit everything from visible light to infrared,
ultraviolet, and
gamma rays. Our eyes sense only a small fraction of the light stars create, so astronomers use a wide range of
telescopes, each tuned to different
wavelengths of light, to capture a more complete view.

Because infrared signals from deep space are often weak, every source of interference needs to be removed from the sensors, even those made by vibrating
atoms. To still the atoms, the device was cooled by liquid
helium to a temperature of -452 degrees Fahrenheit. With room on board for only one year’s supply of the coolant, the whole project became a race against time. It did its job, and the satellite, now defunct, continues to orbit the sky. In the years since, a small community of scientists has proposed a mission to give the satellite a helium recharge to put the sensors back in business. Limited budgets and the development of better technology have kept the satellite switched off.

Despite the short life span of the satellite’s detectors, the mission was a huge success. In less than a year it charted almost 96 percent of the sky. The satellite mapped new
asteroids and
comets until, in early 1984, it captured a glimpse of a star radiating far too much heat for its size and type. We have a good idea about how much heat different kinds
of stars should produce, and something was clearly different about this star. The source of that extra radiation became clear upon closer inspection of the images. The star was encircled by a vast cloud of dust and debris
that held heat. This system,
Beta Pictoris, became the first example of a
solar system caught in the act of being born. A prediction born as intuition and converted to mathematics was confirmed after two hundred years.

Soon after its
formation, our solar system would have looked like Beta Pictoris. This moment of our history was chaotic; rocky debris fragments of different sizes collided with one another as they swirled around the sun. The gravitational pull of the sun meant that heavier material would orbit closer to it, while lighter particles and gas orbited farther away. To some extent, this state of affairs remains in effect today, with the solar system composed of
rocky inner
planets,
Mercury,
Venus, Earth, and
Mars, and gaseous outer ones,
Jupiter,
Saturn,
Uranus, and
Neptune.

Whether the object of a search is Easter eggs, fossil bones, or a new kind of solar system, one discovery typically leads to the next. What once was rare turns up everywhere, often right under our noses. The years since the recognition of the
dust surrounding Beta Pictoris have witnessed the launch of new satellites, the construction of ever-bigger telescopes, and the use of powerful
computers to crunch all the data returning to Earth. This technology has changed our view of the heavens. Far from being a lonely solar system, ours is only one of many in the
galaxy. The sky is filled with other worlds at different stages of their development surrounded by planets of almost every description.

Powerful technology and great ideas have transformed our notions of the heavens. But do not discount the impact of pure luck.

In the wee hours of the morning on February 8,
1969, a massive fireball woke residents of the Mexican state of Chihuahua. A visitor from space had arrived: a large meteorite that broke apart in the atmosphere. After learning of the event, scientists and collectors poured into the area in droves. Given the size of the boom, the collectors had expected a bonanza, but they had no idea of the extent until they looked carefully inside the rock. Tiny white patches interrupted the dull gray body of the rock itself. Meteorites with these specks were known before, but they were incredibly rare. Laboratory work on the few other meteorites with inclusions like these revealed grains that hint at the chemical signature of primordial
rocks of the solar system.

The meteorite exploded into fragments that spread over about twenty-five square miles of desert. Two to three tons of fragments have been collected in the years since the impact. Even today, more than forty years later, pieces are occasionally found.

The impact could not have occurred at a more opportune time. In 1969,
Project
Apollo was in high gear. With
Apollo 8
having circled the
moon just two months before the meteor strike and another as-yet-undetermined
Apollo mission set to land on it, labs across the country were gearing up to investigate the chemistry of
moon rocks. Now, at no expense to the taxpayer, special rocks from space had arrived right on our doorstep. Not only that, but the meteor was so huge prior to breaking up that there were a large number of fragments to share among the different chemistry laboratories capable of making sense of them.

Scientists performed the routine analysis of the atoms inside the rocks. Some of the mineral grains are so similar to those of Earth rocks that they point to a shared history of the bodies of our solar system, just as
Swedenborg,
Kant, and
Laplace predicted. Other minerals can be
dated using the
decay of the atoms inside as a kind of clock. When a mineral forms, the atoms come together as a crystal structure. Once born as a crystal, some of the atoms, such as uranium and lead, change at a regular pace as defined by the laws of physics and chemistry. If you know the relative abundances of the different forms of the atom inside the mineral, and the rates at which they convert to one another, then you can calculate the time since the mineral formed (see Further Reading and Notes for more details).
Uranium 238 converts into
lead 206 very slowly; it takes 4.47 billion years for half the original amount to decay in this way. This slow rate of atomic change makes uranium and lead ideal atoms to measure the
age of very
ancient crystals. The uranium and lead concentrations of the Mexican meteorite point to an age for when the solar system got its start: 4.67 billion years ago.

But what was happening on Earth during these early moments? Direct evidence is hard to come by. In the ideal world, we would have a rock that formed at the moment Earth’s crust cooled and has lain undisturbed for the billions of years since. The easiest
geological conditions to study are those in which one layer of rock lies on top of the next, much like a birthday cake. The deepest layers would be the object of the hunt because typically those would be the most ancient. You could
drill a deep core for them, but this is way too expensive for the typical
geology budget. What’s more, the drilling would be a bit of a shot in the dark: it would be hard to know where to look miles under the surface of Earth. You’d be better served to find places where the ancient rock layers are poking out at the surface of the crust. The challenge with finding these places is that the surface of the planet is continually being reworked. Mountains and oceans rise
and fall. Under the action of such a dynamic planet, rock layers are buried, heated, and then eroded by water and wind. If the ideal geological conditions are regular cakelike layers, imagine a cake pulled asunder, crushed, and then superheated. Now throw 99.99999 percent of that dessert away. The hunger you’d experience trying to eat that cake would be similar to that of geologists who seek to find artifacts of the planet’s formation.

Some places just feel primordial, almost like an ancient landscape frozen in time. At the
Jack Hills in the arid desert of Western Australia, lowland scrub pokes out from orange and yellow bluffs of rock. Aboriginal art lies etched on boulders, the artists having died tens of thousands of years ago. The region’s climate is so hot and dry that the nearby bays and inlets of Shark Bay are home to odd doorknob-shaped mats of microbes. These
microbial communities are some of the most ancient living relics on Earth, with their closest relatives
fossils that are over 2 billion years old. Fittingly, the bluffs of rock that jut to the surface match like jigsaw puzzle pieces to ancient ones buried deeply elsewhere. These are old-looking rocks too; heavily transformed by heat and pressure over time, they carry their history like wrinkles on a face. These rocks from the geological basement have been witness to most of the entire history of our planet.

Befitting such survivors, these layers have experienced eons of torment; from formation inside hot volcanic fluids to great pressures as they lay buried underground, finally to the stresses and strains that came when the layers were wrenched to the surface. Moment after moment is recorded in these layers; the trick, as always, comes from learning how to see the history inside.

Every rock in the ground is an artifact that, when you know how to interpret it, becomes a time capsule, a thermostat, even a barometer of the health of our planet. To wrest these details from stones, we have to zoom from a bird’s-eye view of rock layers all the way down to a microscopic one. The
smallest components of rocks—the individual grains of sand or minerals inside—often
tell the biggest stories. One of these grains, zircon, has unique properties. It is virtually indestructible, and it can survive superheating, high pressure, erosion, and virtually every other torture that the planet can throw at it.

Large, clear crystals of zircon make great fake diamonds. To those interested in the formation of the planet,
zircons are far more valuable than gems, because zircon’s durability makes it an ideal window into the ancient
Earth. The rocks that contain zircons can come and go, but zircons are (nearly) forever. The clocks of
uranium and
lead from the Jack Hills produce a range of
ages from 4.0 to 4.4 billion years.

The chemistry of zircons tells us more than the
age of Earth. It holds a true surprise. The abundances of the various forms of
oxygen inside the crystal can only have come from rock that interacted with
liquid
water as it formed.