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In Atom: An Odyssey from the Big Bang to Life on Earth . . . and Beyond, Lawrence Krauss tackles an enormous task in describing the life of an oxygen atom from its beginnings to its end. On a number of occasions, Krauss abandons the atom to relate scientific ideas, principles, and stories of exploration that are relevant to that time in the atom’s life. Although parts of the book are quite speculative, Atom is a marvelous work that records a possible history of the cosmos from beginning to end. Even though it is written with an approach similar to that taken by David Darling in Deep Time: The Journey of a Subatomic Particle from the Moment of Creation to the Death of the Universe—and Beyond (1989), this work by Krauss is much more complete, drawing upon many new advances in scientific knowledge. Atom also contains similarities to a chapter inThe Periodic Table (1975), by Primo Levi, in which Levi traces the life of a carbon atom for some 235 years after a carbonate rock in which it resides is discovered in 1740.

Although the reader must be willing to exert frequent intellectual effort when reading Atom, the reward is well worth it. Krauss clearly explains the modern ideas of physics, astronomy, geology, and biology and integrates them into the development of stars, planets, and the origin of life. The book is entertaining and easy to read, particularly after the atom reaches Earth. The book generates awe and wonderment about the universe.

Since it would require a quantum theory of spacetime not yet formulated to explain what happened prior to the Big Bang, Krauss starts with that event. At the onset of the Big Bang, which is believed by most scientists to have generated the universe, there were no atoms or elements. Krauss suggests that the entire visible universe would then fit into a volume about the size of a baseball. The energy and density of mass inside that space were inexplicably high. Under those conditions, the four fundamental forces in nature—gravitational, electromagnetic, strong nuclear, and weak nuclear—were all unified, acting as one underlying force for all particles. A battle had been waging between matter and antimatter prior to the Big Bang to determine which one would provide the building blocks of the universe. Although the reason is rather obscure, Krauss points out that a minuscule imbalance occurred in the favor of matter, most likely due to a microscopic asymmetry associated with the fact that time moves forward, not backward.

After the Big Bang, there was an extremely hot primordial soup of elementary particles, consisting of free quarks, electrons, photons, neutrinos, gluons, and their antiparticles. Within a fraction of a second after the Big Bang, the resulting expansion of matter produced some cooling. Quarks were then subjected to the strong nuclear force. Some were attracted together to form the eight protons and eight neutrons that would eventually be involved in the formation of the oxygen atom tracked by Krauss. However, since free neutrons decay into protons, the only neutrons in existence ten minutes after the Big Bang were those that had bonded with protons to form helium nuclei. Based on statistical probabilities, Krauss believes that the building blocks that would ultimately combine to form his oxygen atom had now become twelve key hydrogen nuclei and one key helium nucleus.

Approximately 330,000 years after the Big Bang, as the universe continued to expand and cool, temperatures finally declined enough for atoms to begin forming. Due to localized spatial density variations, gravity began assembling clumps of matter at various locations in the universe. The struggle between gravity pulling inward and gas pressure pushing outward generated interactions that spread the eventual building blocks of the oxygen atom far apart, unlikely to ever get together again. As temperatures continued to drop, molecules began forming and protostars evolved from the gaseous matter.

Of the particles that would finally join to produce the key oxygen atom, Krauss suggests that four of the key hydrogen atoms traveled to a distant pregalactic gas cloud, where they remain unheard from until very late in the story. The other eight key hydrogen atoms and the key helium nucleus take up residence in a huge, pregalactic gas cloud that becomes the breeding ground for new stars. As the battle between gravity and gas pressure finally reaches a state of equilibrium in one of the protostars, a star is born. Four of the key hydrogen atoms and the key helium atom are components of this star. Krauss notes that they are probably kilometers apart. The other four key hydrogen atoms in this galactic cloud are light years away from the new star.

At this juncture, Krauss diverts to discuss the astrophysics associated with the life of a massive star. At times like these, the oxygen atom gets lost in the science, and Krauss and the reader have to refocus on what the story is really about. As the new star generates energy through the process of nuclear fusion, the four key hydrogen atoms within the star are transformed into a helium atom. The star continues to burn, with numerous cycles of expansion and collapse, until after millions of years, it undergoes a supernova explosion. The ensuing shock wave sends the two key helium atoms zooming into space. Due to the force of gravity, they eventually join the other four key hydrogen atoms residing in this galaxy to participate in the life of another star. As this second-generation star evolves, these four key hydrogens are transformed into a helium atom. When the star ultimately undergoes a supernova explosion, the three key helium atoms join to form a carbon atom. Krauss points out that this carbon will likely participate in the formation of a number of organic compounds, including carbon dioxide. Eventually, due to the force of gravity, it is seized by a passing comet.

In the meantime, gravity has been actively organizing localized clumps of dust and gaseous matter into planetesimals (small, solid bodies present in the early stage of solar system development), and eventually into planets in this galactic system. By happenstance, the comet carrying the key carbon atom is attracted to an inner planet where water vapor exists and the conditions for the evolution of life are possible. The key carbon atom bound in a molecule of carbon dioxide interacts with water vapor to form carbonic acid. Carried as a component of acid rain, the key carbon atom becomes chemically integrated into a limestone rock, is subducted into the upper mantle of the planet, and finally reemerges through the vent of a volcano as part of a carbon dioxide molecule.

Approximately one billion years after the Big Bang, the galaxy containing the key carbon atom and the galaxy where the other four key hydrogen atoms reside are pulled together by gravity. The two galaxies pass through each other, ultimately to form a new galaxy, the Milky Way. In the process, the four key hydrogen atoms are joined together to form helium. In one of the spiral arms far from the center of the new galaxy, a star evolves. The key carbon atom and the recently formed key helium atom are brought together in the evolving star. Prior to the explosion of the star, the carbon and helium bond to produce the oxygen atom. When the star subsequently explodes, the resulting shock wave sends the oxygen atom speeding through space.

Attached to an aluminum oxide grain in a large rocky snowball of matter, the oxygen atom begins an orbit near the planet Jupiter. Over a long period of time, the large snowball receives a gravitational kick from Jupiter that sends it through the solar system toward the Sun. As the Sun heats the matter, a tail forms behind the snowball. The resulting comet is gravitationally attracted to the inner planet Earth. Upon entering Earth’s atmosphere, the comet breaks into several pieces. The piece carrying the protagonist oxygen atom crashes into the ocean. Subsequent evaporation returns it to Earth’s atmosphere in a molecule of carbon dioxide. Krauss again diverts to discuss many fascinating aspects surrounding the history of geological, geophysical, and biological evolution on Earth.

After the oxygen atom descends to the Earth in acid rain, it claims a spot in a limestone rock on the ocean floor. Over time, tectonic interactions subduct it toward Earth’s upper mantle. Through the processes of mantle convection and volcanism, the oxygen escapes through a hydrothermal vent and reemerges into the atmosphere in a carbon dioxide molecule. Ingested by a microbe, the carbon dioxide is converted into a complex carbohydrate. When the organism dies, the oxygen atom follows a very familiar course, being buried in Earth’s crust, subducted to the upper mantle, spewed out of a volcanic vent into the atmosphere in carbon dioxide, and eventually ingested back into the life cycle.

As the amount of oxygen builds up in Earth’s atmosphere, due primarily to volcanic activity, living forms are compelled to develop the capability of respiration in order to support more complex cell functions. Nucleated cells develop with mitochondria, the centers for the respiratory function. Larger life forms evolve. Over the next few hundred million years, the oxygen atom witnesses the Cambrian explosion of life, the Paleozoic extinction, the Mesozoic extinction, and a vast parade of different living species, finally participating in human life.

Although the story of the protagonist atom is very speculative and occurs only as the result of a combination of many rare events, Krauss argues that it probably happened just as he told it for at least one of the oxygen atoms that is part of Earth today. Each human being may have inhaled one or more oxygen atoms that followed Krauss’s prescribed course. As a result of such processes, all human beings can rightfully be called “star children,” being composed of atoms generated in stellar evolution somewhere in the universe.

What will happen to the oxygen atom in the future? Krauss speculates about future events associated with Earth, including the possible development of humanlike robots, the evolution of the Sun, and the escalation of the greenhouse effect. After being inhaled by the grandchildren of the current population of Earth, and other, future generations, Krauss predicts that the oxygen atom will be stored in an oxidized rock in Earth’s crust or in a carbon dioxide molecule in Earth’s atmosphere. As the Sun evolves toward a red giant stage, Earth will heat up tremendously. Due to the decreasing gravitational pull of the Sun, Earth will migrate outward to where Mars presently resides. Before Earth is consumed by the blazing heat, Krauss allows the oxygen atom to escape into the cosmos. During its long sojourn on Earth, it experiences more transformations than it will in the rest of its history.

Will the oxygen atom be absorbed by another evolving star and eventually wind up on another living planet? Krauss believes that the odds of its doing so are infinitesimal. He notes that the oxygen atom could wind up in the core of a dead star, as part of a heavier element in some supernova explosion, or even inside of a black hole, never to be seen again. However, he chooses a route for the atom that takes it out of the Milky Way galaxy. The shock wave of a supernova explosion carries it into the emptiness of outer space. Headed in no particular direction, traveling near the speed of light, it may live forever as a free oxygen atom, unless protons, like neutrons, eventually decay. Assuming that this scenario is true, the neutrons and protons of the oxygen nucleus will finally break down into electrons and positrons. Billions or trillions of years into the future, the protagonist atom will no longer exist. Then, does the universe continue to expand or does it collapse in a Big Crunch and the process start all over?

Sources for Further Study

Booklist 97 (February 15, 2001): 1095.

Discover 22 (August, 2001): 78.

Publishers Weekly 248 (March 5, 2001): 75.

Scientific American 284 (April 20, 2001): 106.

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