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Chapter One
Origins of the Earth
INFINITIES AND INFINITESIMALS
Everything in our universe, including the Earth and
its living creatures, obeys the laws of physics, laws
that became manifest in the first moments of time.
Much of what we know to be true about the physical
universe, like the curvature of spacetime and
the fact that electrons are both particles and waves,
is very difficult to visualize, even for people who
spend their lives thinking about such topics.
Moreover, as physicists and mathemeticians probe
ever more deeply, they present us with ever more
mind-boggling concepts, like the idea that sub-atomic
particles may in fact be minute, vibrating
"superstrings" of space, that our four-dimensional
universe may actually be ten-dimensional, that the
observable universe may be much smaller than the
true universe, and that there may be many other
universes besides our own.
Fascinating as these known and speculative
manifestations of physics may be, they prove not to
be central to our story of life. Why? Because when
Earth life was coming into being, some ten billion
years after the universe had come into being, the
laws of physics were a given. Life had no choice but
to evolve in the context of quantum indeterminacy
and gravitational fields and quarks held together by
gluons. Therefore, while these facts underlie all of
life, and constrain what can and cannot occur during
biological evolution, we can describe how life
works without referring to them, in much the same
way that we can describe what a painting looks like
without referring to the absorption spectra of its
pigments.
What is central to the origin of Earth life is the
history of the universe--the cosmic dynamics that
yielded our star, our planet, and the atoms that
form living things. We can tell the story sparingly,
without pausing to define terminology, allowing
the flow of events to suggest the enormous times
and distances involved.
THE UNIVERSE STORY
The observable universe is about fifteen billion
years old. In the beginning, everything that is now
that universe, including all of its space, was concentrated
in a singularity, maybe the size of a pinhead,
that was unimaginably hot (at least
100,000,000,000,000,000,000,000,000,000
degrees) and unimaginably dense. It all let loose
during an event called the Big Bang, a misleading
term in that there wasn't really an explosion. What
happened was that the compacted space expanded
very rapidly, carrying everything else along with it.
During the first three minutes of this expansion,
all sorts of high-energy physics took place that
yielded the current tally of subatomic particles in
the universe, including protons, neutrons, and electrons.
Some of the protons and neutrons fused to
form helium ions, and random clumps developed in
the expanding material so that it was not perfectly
homogeneous. And then things started to settle
down, with the space continuing to expand and
cool until, after several hundred thousand years,
temperatures were low enough that the protons and
helium ions could acquire electron shells and
become stable hydrogen and helium atoms. The
expansion continued for another 15 billion years,
yielding the present observable universe,
1,000,000,000,000,000,000,000,000 miles in
diameter. Whether it will continue to expand or
start to contract back again (the Big Crunch) is one
of the many unknowns of cosmic evolution.
Because the early hydrogen and helium atoms
were distributed inhomogeneously in the expanding
space, close neighbors tended to move closer
and then closer together, attracted by gravity. The
result was that the universe became "lumpy," with
vast gaseous clouds scattered here and there, occasionally
colliding and merging with one another.
These protogalaxies then differentiated, and continue
to differentiate, into billions of galaxies, each
giving rise to billions of stars.
A star starts out as a gaseous cloud, about
three-quarters hydrogen and one-quarter helium.
The atoms are brought together by gravitational
attraction and, as they fall closer together, they
speed up until the temperature is so high that they
are stripped of their electrons and the hydrogen
nuclei start to fuse, forming helium ions. These
fusion reactions release heat, causing the gas to
expand and counterbalancing its tendency to contract.
As a result, the star stabilizes in temperature
and size, often for billions of years, burning its
hydrogen fuel.
Once the hydrogen begins to run out, the rate
of nuclear fusion slows down and the gases no
longer expand as readily. As a result, the star begins
to contract again, eventually becoming so dense
and hot that its helium nuclei start to fuse together,
forming larger nuclei like carbon, oxygen, calcium,
and other "light" elements of the periodic table.
What happens next depends on the size of the
star. A small star becomes unstable at this stage and
puffs away its outer layers, seeding the galaxy with
its newly minted light elements and leaving behind
a remnant known as a white dwarf. A giant star
keeps collapsing, getting hotter and hotter and
forming heavier and heavier nuclei until it starts to
make iron, which it can't burn. When a critical
amount of iron accumulates, the core of the star is
crushed by gravity into what is called a neutron
star, and the shock waves generated by the crushing
process cause a huge explosion in the star's outer
layers--a supernova. Very heavy nuclei, including
radioactive elements like uranium, are created during
the supernova phase, and all the new kinds of
nuclei are released into gaseous clouds where they
cool, acquire electrons, and become atoms.
The gaseous clouds now go on to aggregate
into second-generation stars that are more complex
than their predecessors because they include some
of the new kinds of atoms. The second-generation
stars proceed to burn their hydrogen and collapse,
forming more new elements in the process, and the
released detritus then reaggregates into third-generation
stars that are yet again more complex. Such
birth-and-death stellar cycles are apparently destined
to continue for billions of years into the
future.
THE EARTH STORY
So now we can look at our own context. The Milky
Way is a medium-sized galaxy, and the Sun, located
in one of its spiral arms, is a second- or third-generation
medium-sized star that formed from the
atoms released by a nearby supernova. The Sun has
existed for about 4.5 billion years and has enough
hydrogen to burn for another 5 billion years or so.
During its terminal phases it is expected to become
so hot that the Earth will turn into a cinder.
While the Sun was forming, some of the surrounding
material assembled into small aggregates
that grew and collided and merged with one another
and eventually stabilized as its orbiting planets,
moons, and comets. Importantly, some of these
aggregates, including what is now Earth, contained
generous quantities of the atoms spewed out by
supernovae: These include the iron and radioactive
elements that form the Earth's broiling core, the silicon
that forms its crust, and the carbon, oxygen,
nitrogen, and other elements that are essential for
life. Moreover, comets colliding with the young
Earth provisioned it with yet more atoms from distant
supernovae, and also brought in a great deal of
water in the form of ice. Gases trapped in the
Earth's interior were released through fissures and
volcanos and became trapped by gravity to form
the early atmosphere, and the floating surface settled
into large masses that drift and crash into one
another in continuous geological activity, defining
and redefining the continents and ocean basins.
After about half a billion years of consolidation,
the physical conditions on Earth became such that
life could originate and continue.
Reflections
I've had a lot of trouble with the universe. It began
soon after I was told about it in physics class. I was
perhaps twenty, and I went on a camping trip,
where I found myself in a sleeping bag looking up
into the crisp Colorado night. Before I could look
around for Orion and the Big Dipper, I was overwhelmed
with terror. The panic became so acute
that I had to roll over and bury my face in my pillow.
* All the stars that I see are part of but one
galaxy.
* There are some 100 billion galaxies in the universe,
with perhaps 100 billion stars in each
one, occupying magnitudes of space that I cannot
begin to imagine.
* Each star is dying, exploding, accreting,
exploding again, splitting atoms and fusing
nuclei under enormous temperatures and pressures.
* Our Sun too will die, frying the Earth to a crisp
during its heat-death, spewing its bits and
pieces out into the frigid nothingness of curved
spacetime.
The night sky was ruined. I would never be
able to look at it again. I wept into my pillow, the
long slow tears of adolescent despair. And when I
later encountered the famous quote from physicist
Steven Weinberg--"The more the universe seems
comprehensible, the more it seems pointless"--I
wallowed in its poignant nihilism. A bleak emptiness
overtook me whenever I thought about what
was really going on out in the cosmos or deep in the
atom. So I did my best not to think about such
things.
But, since then, I have found a way to defeat
the nihilism that lurks in the infinite and the infinitesimal.
I have come to understand that I can
deflect the apparent pointlessness of it all by realizing
that I don't have to seek a point. In any of it.
Instead, I can see it as the locus of Mystery.
* The Mystery of why there is anything at all,
rather than nothing.
* The Mystery of where the laws of physics came
from.
* The Mystery of why the universe seems so
strange.
Mystery. Inherently pointless, inherently
shrouded in its own absence of category. The
clouds passing across the face of the deity in the
stained-glass images of Heaven.
The word God is often used to name this mystery.
A concept known as Deism proposes that God
created the universe, orchestrating the Big Bang so
as to author its laws, and then stepped back and
allowed things to pursue their own course. For me,
Deism doesn't work because I find I can only think
of a creator in human terms, and the concept of a
human-like creator of muons and neutrinos has no
meaning for me. But more profoundly, Deism spoils
my covenant with Mystery. To assign attributes to
Mystery is to disenchant it, to take away its luminance.
I think of the ancients ascribing thunder and
lightning to godly feuds, and I smile. The need for
explanation pulsates in us all. Early humans, bursting
with questions about Nature but with limited
understanding of its dynamics, explained things in
terms of supernatural persons and person-animals
who delivered the droughts and floods and plagues,
took the dead, and punished or forgave the wicked.
Explanations taking the form of unseen persons
were our only option when persons were the only
things we felt we understood. Now, with our
understanding of Nature arguably better than our
understanding of persons, Nature can take its place
as a strange but wondrous given.
The realization that I needn't have answers to
the Big Questions, needn't seek answers to the Big
Questions, has served as an epiphany. I lie on my
back under the stars and the unseen galaxies and I
let their enormity wash over me. I assimilate the
vastness of the distances, the impermanence, the
fact of it all. I go all the way out and then I go all
the way down, to the fact of photons without mass
and gauge bosons that become massless at high
temperatures. I take in the abstractions about
forces and symmetries and they caress me, like
Gregorian chants, the meaning of the words not
mattering because the words are so haunting.
Mystery generates wonder, and wonder generates
awe. The gasp can terrify or the gasp can
emancipate. As I allow myself to experience cosmic
and quantum Mystery, I join the saints and the
visionaries in their experience of what they called
the Divine, and I pulse with the spirit, if not the
words, of my favorite hymn:
Immortal, invisible, God only wise,
In light inaccessible hid from our eyes,
Most blessed, most glorious, the Ancient of
Days,
Almighty, victorious, thy great name we
praise.
Unresting, unhasting, and silent as light,
Nor wanting, nor wasting, thou rulest in
might,
Thy justice like mountains high soaring
above
Thy clouds which are fountains of goodness
and love.
To all, life thou givest, to both great and
small;
In all life thou livest, the true life of all;
We blossom and flourish as leaves on the
tree,
And wither and perish, but naught changeth
thee.
Thou reignest in glory; thou dwellest in
light;
Thine angels adore thee, all veiling their
sight;
All laud we would render: O help us to see
'Tis only the splendor of light hideth thee.
Walter Chalmers Smith, 1867
And then I wander back twenty-six centuries
to Lao Tzu and the first chapter of the Tao Te
Ching:
The Tao that can be told is not the eternal
Tao.
The name that can be named is not the eternal
name.
The nameless is the beginning of heaven and
earth.
The named is the mother of ten thousand
things.
Ever desireless, one can see the mystery.
Ever desiring, one sees the manifestations.
These two spring from the same source but
differ in name; this appears as darkness.
Darkness within darkness.
The gate to all mystery.