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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 |