April 2010 Philadelphia Chapter of Pax Christi U.S.A.

The Birth of Earth

Our planet formed relatively late in the evolution of the universe. The initial blossoming forth of the universe (the “big bang”) began about 13 or 14 billion years ago. Our Earth is only about 4 or 5 billion years old, and it had to be that way. Why? It’s a fascinating story.

What emerged first at the beginning of the universe was simply empty space, a miniscule volume, rushing from an incredibly hot temperature into a rapid expansion and cooling. There also emerged time itself. And that is all there was— space and time.

The first matter began to emerge out of the “quantum void” with the appearance of matter-antimatter pairs. In complete violation of classical physics, these matter-antimatter pairs emerged out of the space-time continuum, literally out of nothing. How can that be? Quantum physics allows such things, even if classical physics does not.

Of course, matter and anti-matter immediately annihilate one another as soon as they come into contact, and most pairs suffered this fate. However, the universe was expanding so rapidly that some survived. Through some unexplainable mechanism (some purposeful goal embedded in the evolutionary process), there was a slight excess of matter particles over antimatter particles. It is from this slight excess that the entire material of the universe is derived.

This earliest form of matter consisted of electrons and quarks, the quarks soon combining to form protons and neutrons. The formidable task of combining protons and neutrons into elements began, but could not proceed far. Most of the protons, about 75 percent, simply captured electrons and became hydrogen atoms. The rest were able to combine through the process of nuclear fusion to become helium, along with a sprinkling of some other light elements.

Up to this time, the universe had been opaque, the photons of light being continuously captured and released by highly energetic particles and never being able to escape. With further cooling, the light was able to travel significant distances and the Universe became transparent (And God said “Let there be light!”).

It was now time for the gas and dust to become gravitationally attracted and coalesce into stars and galaxies. However, the future did not look hopeful, as not much can be put together simply from hydrogen and helium. Nonetheless, stars were formed, some rather tiny, some middle-sized like our sun, and some really big.

As the stars-to-be began attracting more and more gas and dust to themselves, they experienced great compression from the gravitational forces and as a result interior temperatures began to rise. If the mass was big enough the temperature could rise to the millions of degrees needed to begin nuclear fusion, the process of combining neutrons and protons to form elements beyond helium. So the universe, unable to make higher elements simply from the expansion process, devised another way to make them by cooking them (in the process of nuclear fusion) in the interior of stars.

The smallest stars did not have enough mass to raise interior temperatures high enough to have much nuclear fusion. As a result, they glowed faintly and aged slowly. Any planets which might have formed around them would have very limited potential, since there would be no higher elements.

Middle-sized stars like our sun would become hot enough to ignite nuclear fusion reactions and furthermore the fusion reactions would release energy, causing the interior temperature to rise even higher. After a period of fusing hydrogen to helium, the temperature would rise enough to gradually produce higher elements, although not beyond the next twenty or so in the periodic table even under the best conditions. Among the elements produced would be carbon, oxygen and nitrogen,

elements essential for life, so, in principle, living creatures would have the material from which they could have evolved. The problem, of course, is that the required elements would be present in the interior of the star and not in the planets where life would have to dwell.

These middle-sized stars would burn their nuclear fuel relatively slowly, over a period of about ten billion years, at the end of which they would gradually expand into less dense and faintly glowing objects. Such, indeed, will be the ultimate fate of our own sun, which at this point is about half way through its life.

The largest stars are massive enough that they reach the very highest temperatures, thereby triggering nuclear fusion to produce most of the higher elements and burning their fuel rapidly. When they have consumed most of their nuclear fuel, these stars undergo a violent explosion, becoming many times brighter than a typical star and scattering debris from their interior far into the surrounding space. The debris itself becomes even hotter and triggers nuclear fusion to form the remaining higher elements. A star in such a state is known as a “supernova.”

In our little corner of space, out in one of the spiral arms of the Milky Way galaxy, such a supernova event took place. From the debris, new stars were born, one of which was our sun. It was a middle-sized star, destined to have a lifetime of about ten billion years and to become hot enough to trigger nuclear fusion and produce solar radiation. Out of some of the remaining debris, an accretion disk formed, similar to the rings of Saturn. Most significantly, having had its origin in the supernova event, the debris contained all the chemical elements and therefore provided adequate material for life. With time the accretion disk resolved into various planets and moons, one of which was Earth.

It is fascinating how the evolutionary process is always able to find ingenious ways around what seem insuperable difficulties. The solution always comes as a surprise. Here we have the problem that the elements need to be produced in a super-hot cooker but used for life in a much cooler location. Impossible! How can the elements be moved from the one place to the other? Enter the supernova. Spectacular! Elegant! Effective! Wow, are we lucky!

Dom Roberti

Dom Roberti, PhD, is a member of CPF

http://www.ecospirit.cpfphila.org/