Lonely Planets
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believe any of these egotistical fantasies, but the reflexive reaction
against these views can be as illogical as the narrow thinking that
prompted them.
Sure, humans have historically overemphasized our role in things and
foolishly imagined that we were “conquering nature” and running the
world, where at best we’ve been temporarily mucking it up. Sure, we
need the microbes more than they need us. If they disappeared from the
face of the Earth, we would perish. If we disappeared, most of them
would not notice. But microbes, without us, are not capable of noticing
anything. Through us the microbes have found a mind, a voice. It is
foolish to ignore that human evolution represents a new phase in the
life of Gaia,* a phase with enormous potential and peril. It’s merely a
matter of perspective whether you regard Earth as planet of the
microbes or planet of the apes. Each brings essential qualities to our
*The Gaia Hypothesis, a scientific portrait of a living Earth, has implications for life on other planets that will be discussed in chapter 17.
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home world. I believe, as Teilhard argued, that mankind is not just
another species, but an important evolutionary phenomenon—the pre-
cursor of the psychozoic age.
L O V E R S O F E X T R E M E S
Now, having found mind and the beginnings of technological prowess,
Earth’s biosphere is starting to take a look around, exploring the neigh-
bor planets for the first time, and searching for life in the bright and
dark corners of the solar system. Much of this search takes the form of
self-examination, seeing the home world with new eyes.
I’ve been describing the history of life as a series of leaps to greater
complexity and organization culminating, at least so far, in the psy-
chozoic age. While all this has been going on, over the 4-billion-year
life of Earth’s biosphere, other evolutionary dramas have been playing
out. Life has expanded on its bag of chemical tricks to facilitate sur-
vival in a bewildering array of environments.
In recent years, we’ve discovered life in the strangest of places: in
unlikely corners of our planet where no one had thought to search
because they seemed so obviously uninhabitable. We’ve found bacteria
thriving in acid so strong that it would dissolve your skin instantly, and
creatures soaking contentedly in superheated thermal springs above
two hundred degrees. Some of these hyperthermophiles, or extreme-
heat-loving organisms, require temperatures above the normal boiling
point of water to survive. At the opposite extreme are those that sur-
vive in intense cold. In frigid arctic tundras that appear lifeless, we’ve
found colonies of bacteria hiding out inside frozen rocks. We’ve even
found organisms that can survive after being frozen for weeks in liquid
nitrogen!
The green plant Welwitschia mirabilis can survive for thousands of
years in places with only one centimeter of rainfall per year. The Dead
Sea, it turns out, is alive with salt-loving bacteria and algae. In 1997,
Japanese scientists discovered a species of marine worm living in an
ocean trench twenty-one thousand feet beneath the sea at a crushing
pressure 650 times that of sea level. Bacteria have survived for 3 million
years in Siberian permafrost at fifteen degrees below zero with no sun-
light, air, or food. They don’t do very much down there but survive
simply by waiting, for eons if necessary, until the ground thaws and
they can resume living at a healthier clip.
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Large, diverse communities of previously unknown organisms crowd
the hot, nutrient-rich waters surrounding “black smokers,” volcanic
vents on the bottom of the sea. The denizens of these recently discov-
ered ecosystems include sulfur-eating shrimp and giant tube worms up
to ten feet long. As weird and unearthly as these deep-ocean communi-
ties seem to us, many scientists are starting to think that our most dis-
tant ancestors came from just such a place.
There are even bacteria living a mile underground and eating nothing
but basaltic rock and water.* In fact, it now seems possible that most
life on our planet is in the “deep Earth biosphere,” a realm extending
miles underground whose existence we never before suspected. This
would be the biological equivalent of “dark matter” in that the major-
ity of life even on our own planet could as yet be unknown to us. We’ve
been sharing a planet with these unlikely creatures for billions of years,
but who knew?
Our own planet is crawling with “aliens.” We continue to find
extremophiles (lovers of extremes) that break our conceptual barriers
of life’s range in temperature, pH, diet, and pressure. They show us that
life is even more robust, adaptable, and resourceful than we imagined,
and this encourages us to think that it will find ways to persist in
diverse and extreme environments on other planets.
In fact, life may not even need a planet. When the Apollo 12 astro-
nauts retrieved pieces of the old Surveyor 3 spacecraft, which had been
sitting idle in a lunar crater fully exposed to the harsh radiation and
vacuum of space, investigators back on Earth were shocked to find
viable Streptococcus bacteria that had survived a three-year stay on the Moon. Who is to say that living creatures cannot survive longer spells
in outer space?
This possibility was amplified by another recent discovery: bacteria
such as Deinococcus radiodurans that live happily inside nuclear reac-
tors, flawlessly reassembling their damaged genomes from hundreds of
fragments, despite radiation doses a thousand times stronger than those
that would kill a human. Suddenly, the merciless radiation of space
seems less of a barrier to survival than it once did. Scientists have also
revived bacterial spores that had been encased in amber for at least 25
*Fontenelle anticipated this in the seventeenth century when he wrote about “innumerable small worms, living in imperceptible gaps and feeding themselves by gnawing on the substance of the stone.”
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million years. Such findings have revived talk, or at least whispers, of
“panspermia,” the idea that Earth life may not have originated on
Earth.
P A N S P E R M I A R E C O N S I D E R E D
Though Earth’s creatures live in a hugely diverse range of environments
and power ourselves with an impressive variety of chemical energy
sources, we all use the same basic chemical operating system. There is
no “think different.” It’s a complete monopoly.* What is the meaning
of this?
A remarkable aspect of Earth’s story is that the planet became inhab-
ited as soon as it was habitable. Once the sterilizing impacts died down, Earth sprang to life—in less than a couple hundred million years, and
maybe much faster. Then, a short while after life on Earth started, it
had already constructed the fantastically intricate, interlaced chemical
engines of DNA replication, protein transcription,
and a great many
more standardized cycles and systems that would seem so elegantly
conceived if only they seemed conceived. Life did not take billions of
years of evolution to perfect these fine and fertile, far-flung factories.
Not only the origin but most of the essential chemical evolution of life
on Earth happened before you could say “evolutionary divergence.”
Does this mean that, given half a chance, a biosphere with such
refined chemical machinery is easy to make? A widely accepted inter-
pretation is that on a planet like ours chemical evolution leads rapidly
and inexorably to life. This inference is a mainstay of scientific belief in
a universe with many inhabited worlds.
Although it is not popular to do so, we could also look at this auspi-
cious timing as supportive of the theory of panspermia, elaborated by
Arrhenius in 1903—the idea that Earth life was seeded from elsewhere.
If space contains spores wafting and waiting for watery worlds, life
would be expected to spring up instantly as soon as it found a stable
ocean. The strongest objection is that we cannot imagine spores that
would survive the drift between star systems. This is a valid argument
against panspermia, but not a damning one. Time and again, evolution
has proven more clever than we are at solving survival puzzles. I won-
der if we really don’t like the idea because it gives us the creeps.
*Hey, could I be channeling Bill Gates?
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A far-out variant is “directed panspermia”—the idea that some crea-
tures from elsewhere in the galaxy have played cosmic Johnny
Appleseed, deliberately spreading life through the universe. That could
explain the sudden appearance of chemically sophisticated life. Could
the first living cells on Earth have been designed by a species with very
advanced biotechnology?*
If this strikes you as pure science fiction, consider the biotechnology
progress (and I use the word loosely) of the last decade. Let’s assume
for a second that we don’t soon commit high-tech suicide with the
genetically modified tomato that ate Manhattan. Can you imagine the
biotechnology and space technology we might possess in just one hun-
dred years, in one thousand years? It doesn’t stretch the imagination
much to think that we could soon be able to do some directed
pansperming ourselves. So why does it seem like such a fantastic notion
that someone else may have done so?
We hate the idea of directed panspermia because it demotes us, like
the Neoterics in “Microcosmic God,” to being the product of someone
else’s ingenuity. It mocks our current biology and origin-of-life studies,
to say nothing of our egos and established sense of place in the world.
Our rational minds whir into action, finding logical objections to safe-
guard us from the disturbing thought. How ironic if science should
have slain all obvious creator gods only to find that some godlike aliens
had created us in their image many billions of years ago.
This model could actually meld the supposedly inimical theories of
intelligent design creationism and Darwinian evolution. Life evolved
elsewhere by natural selection to the point where it could develop
advanced biotechnology. It then proceeded to spread intelligently
designed seeds throughout the universe. These took root on Earth,
where life evolved by natural selection to the point where it is now
again starting to muck around with intelligent design of organisms.
This is not a favored explanation, because scientists don’t like these
kinds of explanations. Some people like them very much. But to us, it vio-
lates Occam’s razor. It is logically almost the same as invoking a biblical
miracle, only aliens, unlike gods, are scientifically acceptable creatures.
A frequent objection to panspermia is that it does not solve the
origin-of-life problem but simply pushes it out into space. Life still had
*What if we find out that some multigalactical corporation owns the patent on DNA-protein biochemistry and they come back through our system demanding licensing fees?
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to get started somewhere. Obviously, this is a lame argument against
panspermia.
A much less radical variant that’s come into vogue in the last few
years is “impact panspermia” or “transpermia.” In the mid-1980s we
realized that some of the meteorites in our collections are actually
pieces blasted off of the planet Mars. There are several lines of evidence
for this, but the clincher is that some of these rocks have bubbles of
trapped air that exactly match the measured composition of the
Martian atmosphere.
Ever since we learned that rocks from Mars have landed on Earth,
we’ve wondered whether life could stow away and ride between
worlds. Were meteorites the bees that cross-pollinated the flowering
planets, carrying the seeds of life across the vacuity of interplanetary
space? Especially when the solar system was young and unruly, with a
nonstop demolition derby of planetesimals constantly spraying the
planets with each other’s shrapnel, any critters that could survive the
launch and the journey would have had no problem hitching a ride to
another world. So, we cannot regard the early environments of the
planets as isolated systems, quarantined by space. Maybe, in their early
days, the planets were all sneezing on one another, sharing germs, with
meteorites as the vector. If any of them became infected with life, the
others would quickly catch it, too. It is conceivable that our earliest
ancestors lived on Venus or Mars and that we are all descendants of
interplanetary immigrants—or should I say resident aliens?
According to this picture, we started out as a multiplanet biosphere
(a biopolysphere?). Gaia was born as planetary “Siamese triplets”
joined by meteorites. Then, when the rates of interplanetary transfer
declined, the three became isolated, and Earth was more or less on its
own. I will discuss the fate of the other two orphaned biospheres in
ensuing chapters. Transpermia would have slowed down before it effec-
tively stopped. In an intermediate stage, perhaps long-lost Martian and
Venusian microbial cousins occasionally arrived on the shores of Earth,
after millions of years of isolation, stirring the genetic pot in interesting
ways.
Now, fueled by the discovery of possible fossils in one of our Mars
rocks, we are experiencing a revival of the nineteenth-century idea that
life might have arrived on Earth in falling meteorites. We are attacking
the problem from several angles with twenty-first-century science.
Could anything have survived the impact that launched these rocks into
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space? We test for that with impact simulations using high-speed guns.
Could they have survived the journey through space and their fiery
arrival on Earth? With sophisticated computer models of orbital
dynamics, we follow the paths of impact shrapnel from Mars (and
Earth and
Venus) to see how likely they are to reach another planet and
how long the journey would take. Experiments in space and in terres-
trial laboratories allow us to study the survival of organisms subjected
to the hardships of space travel.
Microbes are much tougher than the rest of us. The damn things are
hard to kill. Thank Gaia they’re mostly on our side. They’ve survived
experiments with intense radiation, heat, cold, vacuum, shock pres-
sures, and that ear-crushing tape of bad rock music that the U.S.
Marines used to flush out Manuel Noriega. So far no showstoppers
have been found to affect the survival of microbes in space.
Even given all of these intriguing alternative possibilities for life’s ori-
gins, my instincts are in accord with the majority scientific opinion. I
think that planets, Earth included, probably make their own life. Why?
Because they can. The steps to life on Earth seem promising without
any external help or prompting. As for the possibility that life here was
deliberately seeded, all we can do is smile up at the stars, shrug, and
keep looking for the missing links in our cosmic genealogy, keep
searching heaven and earth for our roots.
So What?
9
There is that within us which believes us worthy of
the stars.
Image unavailable for
—SALMAN RUSHDIE, The Ground Beneath Her
electronic edition
Feet
Image unavailable for
Intelligent life understands the void must be filled.
electronic edition
—CONVERSATION BETWEEN TWO VENUSIANS
I N The Quiet Invasion B Y S A R A H Z E T T E L
B E T W E E N T H E L I N E S
We could look at Earth life as a trivial by-product of the immense
cycles of galactic ecology, something odd that happened on one small
planet, in a random spiral of a largish but unremarkable galaxy. We are
that, but we are something much more. Earlier, I described Earth’s bio-
sphere as the Sun’s way of creating life. Well, our star is a product of
the Milky Way galaxy, which coalesced from the cooling ashes of the
big bang. If the universe is a self-tilling orchard slowly cultivating life
and mind, then we, Earth’s awakening biosphere, are a bright flowering
of the vine. We strongly suspect that there are others.
It all really boils down to two questions: