and, I’ll bet, neither can you. But does that mean that such alternate
biochemical systems do not exist, or merely that we are currently too
ignorant or too blinkered by our assumptions to imagine them? We
should not confuse the limitations of our own tiny intellects with limi-
tations on the creativity of Cosmic Evolution. Our universe is full of
varied environments and we have no idea what kinds of chemistry are
occurring, no inkling of what’s crawling in alien seas of unknown com-
position.
Our evolution has expertly exploited the idiosyncrasies of carbon
and water. After 4 billion years of adapting to and building on these
peculiarities, of course these materials seem pretty special to us. We are
built of carbon molecules, floating in an ocean of water. We still live in
that ocean, only now we carry it around within our cells. You can taste
it in our blood, sweat, and salty tears. How might this immersion warp
our perspective?
We have many ways of justifying our “carbaqueous” assumption,
but sometimes I wonder if the real motivation is not simply that we’d
be lost without it. With it we have narrowed the scope of possibilities
enough so that we may apply science to the problem. Once we’ve nar-
rowed life’s needs down to one condition—water—we can look around
the universe for water worlds and apply our theories toward predicting
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where they should be found. Our “life needs water” paradigm is born
of pragmatic necessity, not solid scientific deduction. We need it so that
we can do science.
That’s fine. We do have to start somewhere, especially when taking
on a subject as wide-open as the question of extraterrestrial life. But,
when we repeat something frequently enough, it can work its way into
our psyches. We forget the shallow basis on which we’ve reached our
tentative conclusion that life needs carbon and water. What started as
an educated guess becomes a consensus reality.
Unfortunately, the justification boils down to “that’s the way it
works here and we can’t imagine any other basis for life.” It is like
someone who does not know how to design watches finding an unbe-
lievably exquisite watch, dissecting it, and declaring, “This is so per-
fect, it has to be the only way that a watch can be put together.”
There’s no way that we could have designed something that works as
well as our own biochemistry, so how can we state confidently that
there’s no other substance in the universe suitable for this kind of con-
struction? If our metabolism and structure were based on some chemi-
cal system other than carbon chemistry, on a planet without liquid
water, would we know anything about this carbon potential? In many
ways, some obvious and some subtle, our world has been remade by
life to look like one in which carbon is the only “natural” source of real
complexity. Whether or not this is really true, the world would seem
this way. So we might be fooling ourselves about carbon.
By the time any kind of life—made by any chemical system, carbon
or not—finally evolves consciousness, it will be stunningly well adapted
to its world, and its world thoroughly changed (as our world has been)
by its biochemistry. This life, upon first examining the universe, will
conclude that life can only evolve using its own peculiar kind of chem-
istry. Curious scientists of any chemical construction would observe
many features of their universe that seemed to confirm this view.
I know it won’t sit well with some of my carbon-based, and carbon-
biased, friends, but I choose to remain an agnostic with respect to the
carbon religion. No, agnostic isn’t right. I believe in carbon. I worship
it. Sign me up for the carbon church. I’ll show up every Sunday morn-
ing and do the DNA dance. But to believe, must we swear that carbon
is the true and only way, forever renouncing all other elements?
Some scientists, coming from a biochemical background, even talk
about what we can learn by sequencing alien DNA and comparing it to
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265
our own. To me this seems as ridiculous as dissecting crashed saucers at
Roswell. Expecting to find DNA elsewhere is like expecting a Star Trek
universe with humanoid aliens who speak English and insist that we
join them for dinner at eight. A chemical hereditary system, like a lan-
guage, is the result of a complex evolutionary process filled with ran-
domness, contingency, and frozen-in accidents.
Might life use completely alien chemical systems elsewhere? The
question is not exactly science, because it is difficult to think of a scien-
tific way to address it. It is really a question of natural philosophy.
We have to be careful when stating what is impossible. Different
chemical environments may breed unforeseeable sources of chemical
order. And what about life that doesn’t need chemistry at all? Why not
life on different spatial or temporal scales? Who are we to say that the
universe couldn’t make some kind of complex, self-organizing, evolving
structures using its gravitational or nuclear forces, forming living struc-
tures that are too large or small for us to notice? Life at the scale of
molecular clouds or even galactic superclusters? Why not life, and even
civilization, at the level of elementary, subatomic particles, where
empires that dwarf any in human history rise and fall in a nanosecond,
at a level completely invisible to us? Life so fast or slow that we don’t
notice it? Why not? No reason. No answer.
Time and again we think we know more than we do. We may never
be able to imagine an alternative kind of life, but I bet we will eventu-
ally come across one.
Living Worlds
17
Throughout the continuum as we know it (and a good
deal more, as we don’t know it) there are cultures
Image unavailable for
that fly and cultures that swim; there are boron folk
electronic edition
and fluorine fellowships, cuprocoprophages and
(roughly speaking) immaterial life-forms which swim
and swirl around each other in space like so many
pelagic shards of metaphysics. And some organize into
super-entities like a beehive or a slime-mold so that they live plurally to
become singular, and some have even more singular ideas of plurality.
—THEODORE STURGEON, The Widget, the Wadget, and Boff
G A I A : I S E A R T H A L I V E ?
Using a natural philosophy approach, perhaps we can study life’s uni-
versals without simply projecting visions of our own kind out into the
cosmos. Two controversial new fields of thought promise to help lift
astrobiology beyond this conundrum of self-reference. These are the
Gaia hypothesis and complexity theory.
The Gaia hypothesis, named after the Greek Earth goddess, was first
proposed in the mid-1970s by James Lovelock, a British atmospheric
scientist and inventor, and American microbiologist Lynn Margulis.
Margulis is the
mother of serial endosymbiosis theory, which states that
major evolutionary innovations occur when more complex forms of life
arise out of symbiotic collectives of smaller organisms (as described in
chapter 8).
How far can we extend this principle? Gaia scientists regard Earth in
its totality as one giant superorganism incorporating many parts of our
planet that traditional science sees as nonliving.* The atmosphere and
*Though many older, prescientific traditions have long perceived a living Earth.
Living Worlds
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oceans are the breath and blood, and the rain forests the lungs of this
great global beast. Human culture is, perhaps, its awakening mind.
Gaia suggests that life is seen as not merely incidental, but integral to
the evolution and functioning of the planet. Gaia is a theory of biology,
but also one of Earth history, geochemistry, and climate. The Gaian
approach toward the Earth sciences is “geophysiology,” studying
Earth’s functioning and health as a physician might approach a patient.
In 1988, as a graduate student, I attended the first major main-
stream scientific conference on the Gaia hypothesis, sponsored by the
American Geophysical Union in San Diego. It was fascinating to watch
skeptical traditional scientists do battle with those from the new Gaian
camp as they attempted to get Earth scientists to take their new
approach seriously.* Science still doesn’t quite know what to do with
the Gaia hypothesis, because it isn’t science-as-usual. Yet it is more than
just a pretty metaphor. The Gaia hypothesis is guiding the way some
biologists model life and its role on Earth, even as other (mostly older)
biologists completely dismiss it.
Gaia actually began as an idea about exobiology. James Lovelock,
consulting for NASA during the design of the Viking life-detection
experiments, was thinking about how to look for life on Mars. He real-
ized that the unusual atmosphere of Earth is by far its most distinctive
sign of life. In considering the global properties of life that might be
observable from another planet, he started noticing the many ways in
which Earth’s biosphere behaves like a giant living organism. In 1974,
he and Margulis presented the Gaia concept in a paper called “Bio-
logical Modulation of the Earth’s Atmosphere,” published in ICARUS,
International Journal of Solar System Studies.
The Gaia hypothesis has caused a quiet revolution among Earth sci-
entists, many of whom are now realizing that life participates deeply in
the physical evolution and functioning of Earth. A small school of scien-
tists has fully embraced Gaia and dedicated their careers to it directly. A
much larger group has been more guardedly receptive to the viewpoint,
incorporating it into their work, or at least their worldview.
The Gaia perspective views evolutionary change as a creative inter-
play between biosphere and Earth—an intricate partner-dance between
life and the changing planet in which neither seems to be leading. Life
*My friend Dorion Sagan suggested that we try to get everyone to gather one morning and run down the beach naked yelling, “The Earth is alive!” but this idea never caught on.
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on Earth is no accidental collection of organisms lucky enough to find a
hospitable planetary home. Rather, life has largely created the world we
know. Life, we are learning, has altered many of Earth’s basic physical
properties, investing the air, the rocks, and the water with qualities they
would not possess on a dead world. Thus, Gaia has important implica-
tions for the kind of relationships that biospheres can have with plan-
ets, and this should inform the way that we search for other inhabited
worlds.
With a Gaian picture of evolution we see that some properties of the
“nonliving” parts of Earth are actually encoded in the DNA of the
world’s organisms. Are other planets blessed with their own genomes?
It seems beautiful and true, but is it science? Some scientists complain
that the hypothesis is more hype than thesis. They say there is no way
to test or falsify it. Yet, the Gaia perspective has clearly led to some
good science and to a new framework guiding some of the science we
were already doing. In my view, it’s right on the border of science and
natural philosophy.
Gaia scientists have discussed the significance of Earth’s unusual
atmosphere, which is drastically out of equilibrium. Without the inces-
sant, life-driven chemical cycles that permeate our world, the oxygen
and methane would rapidly react, leaving only CO2 and water, produc-
ing a mix of gases that we would find unrecognizable and certainly
unbreathable. The strange brew we breathe would never be found on a
nonliving world.
Gaia proposes that the cumulative activity of all life on Earth acts to
keep conditions here stable and comfortable for life. This happens by
the evolution of numerous negative feedbacks in which the growth,
death, or evolution of organisms creates environmental changes, which
in turn affect the growth and evolution of other organisms. The net
effect acts to pull the climate and various chemical balances back
toward a certain moderate range if they begin to stray.
Short of comparing and contrasting numerous inhabited worlds, you
can’t do an experiment to test the idea as a whole, but you can look for
active feedbacks on Earth that may be part of such a system. For exam-
ple, some plankton act, collectively, as an air conditioner for the
oceans. When the water gets warm, these guys get frisky and start mul-
tiplying. Their growth produces a chemical called dimethylsulfide
(DMS), which diffuses up into the atmosphere. DMS is great for seed-
ing clouds. As the amount of DMS rises, clouds build up over the
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269
ocean. The ocean surface cools off, which chills out the plankton orgy.
The production of DMS then declines. As a result, it doesn’t get too
cloudy or too sunny for long, and ocean temperature remains in a mod-
erate range favored by life.
The Gaians suggest that such mechanisms have been biologically reg-
ulating conditions on Earth for billions of years. This homeostatic self-
regulation makes Gaia very much like a living organism, with the atmo-
sphere and oceans behaving like circulatory and respiratory systems.
However, obviously Gaia is not like any other organism we know in
some important ways. For example, it has not reproduced, although
you can’t say we aren’t trying.
How deeply ingrained is the biosphere in the physical functioning of
our planet? We don’t know. Gaian science endeavors to find out. It
could go very deep indeed. Life clearly has hold of the atmosphere and
oceans. Numerous cycles connect the atmosphere with the chemical
state of Earth’s interior rocks. Can life have actually assumed control of
the plate tectonics that controls all terrestrial geology? If so, then the
entire thermal evolution of the Earth is controlled by life.
>
Does it really go that deep? Or might Gaia be a spherical superorgan-
ism riding around on a nonliving core? How could you define the
boundary dividing creature and core? Perhaps by looking for a level, at
some depth within the Earth, where things are exactly as they would
have been if life had never come along. When it comes to the deep inte-
rior of the Earth, we don’t yet know if Gaia is holding the reins or skill-
fully riding bareback.
The Gaia hypothesis reveals life to be a planetary-scale phenomenon
with a cosmological life span. Gaia can help us identify those global
qualities that distinguish planets having billions of years of life
ingrained in their cyclic chemical activity from those orbs not blessed
by this world-altering magic.
C O M P L E X I T Y : L I F E B E Y O N D W H A T W E K N O W
Complexity theory is the study of self-organization in nature. You’ve
heard of the second law of thermodynamics: things fall apart. Entropy
will get us all in the end, leaving nothing but bland disorder. Everything
runs inevitably downhill into dull formlessness. Yet look out the win-
dow or stare at your hands. What we actually see around us is not a
gray and featureless sea of entropy but a living world overflowing with
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stunning and profligate order. What saves us from the tyranny of
entropy is an amazing property of matter: in certain conditions, in the
presence of a flow of energy, it self-organizes, forming ordered struc-
tures, in seeming defiance of the second law. Complexity theory is the
mathematical study of these emergent, spontaneous pockets of order.
The simplest example of emergent complexity is a whirlpool sponta-
neously forming in a flowing stream. The most complex example may
be a living organism, or a society of organisms.
Some scientists are starting to see life as the most refined manifesta-
tion of a universal tendency toward self-organization. Given half a
chance, order emerges from chaos, and given optimum conditions, mat-
ter keeps on self-organizing until it can get up, crawl around, and write
poetry. What I find incredibly exciting about this new field is that it
seems to be pointing toward a mathematical account of living systems
that goes much deeper than merely “reverse engineering” the life here
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