One of the basic propositions of A Simple Explanation of Absolutely Everything is what I call the Simple Golden Rule--everything, no matter the scale, reaches out to others and "holds hands" to create something larger than itself that can only come about through cooperation with others.
In the diagram below, you can see how everything "levels up" to contribute to larger and larger structures. Up near the top of the diagram, we reach the global or "Gaia" scale of organization and consciousness.
In this article reprint, from his 2016 book Earth In Human Hands, David Grinspoon lays out his observation that all planets in the Universe will be either fully alive and teeming with life, or fully dead and devoid of life. Grinspoon presents an explanation of the Gaia hypothesis that links lifeforms and minerals in a synergistic dance that requires us to think of the Earth as a living form. I am reprinting this article from Nautilus Cosmos so that you can see how the Simple Explanation's "building upward" orientation contributes to the Gaia hypothesis.
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Why Most Planets Will Either Be
Lush or Dead
BY DAVID GRINSPOON JANUARY 12, 2017
Can
a planet be alive? Lynn Margulis, a giant of late 20th-century biology, who had
an incandescent intellect that veered toward the unorthodox, thought so. She
and chemist James Lovelock together theorized that life must be a
planet-altering phenomenon and the distinction between the “living” and
“nonliving” parts of Earth is not as clear-cut as we think. Many members of the
scientific community derided their theory, called the Gaia hypothesis, as pseudoscience,
and questioned their scientific integrity. But now Margulis and Lovelock may
have their revenge. Recent scientific discoveries are giving us reason to take
this hypothesis more seriously. At its core is an insight about the
relationship between planets and life that has changed our understanding of
both, and is shaping how we look for life on other worlds.
Studying
Earth’s global biosphere together, Margulis and Lovelock realized that it has
some of the properties of a life form. It seems to display “homeostasis,” or
self‐regulation. Many of
Earth’s life‐sustaining qualities
exhibit remarkable stability. The temperature range of the climate; the oxygen
content of the atmosphere; the pH, chemistry, and salinity of the ocean—all
these are biologically mediated. All have, for hundreds of millions of years,
stayed within a range where life can thrive. Lovelock and Margulis surmised
that the totality of life is interacting with its environments in ways that
regulate these global qualities. They recognized that Earth is, in a sense, a
living organism. Lovelock named this creature Gaia.
Margulis
and Lovelock showed that the Darwinian picture of biological evolution is
incomplete. Darwin identified the mechanism by which life adapts due to changes
in the environment, and thus allowed us to see that all life on Earth is a
continuum, a proliferation, a genetic diaspora from a common root. In the
Darwinian view, Earth was essentially a stage with a series of changing
backdrops to which life had to adjust. Yet, what or who was changing the sets?
Margulis and Lovelock proposed that the drama of life does not unfold on the
stage of a dead Earth, but that, rather, the stage itself is animated, part of
a larger living entity, Gaia, composed of the biosphere together with the
“nonliving” components that shape, respond to, and cycle through the biota of
Earth. Yes, life adapts to environmental change, shaping itself through natural
selection. Yet life also pushes back and changes the environment, alters the
planet. This is now as obvious as the air you are breathing, which has been
oxygenated by life. So evolution is not a series of adaptations to inanimate
events, but a system of feedbacks, an exchange. Life has not simply molded
itself to the shifting contours of a dynamic Earth. Rather, life and Earth have
shaped each other as they’ve co-evolved. When you start looking at the planet
in this way, then you see coral reefs, limestone cliffs, deltas, bogs, and
islands of bat guano as parts of this larger animated entity. You realize that
the entire skin of Earth, and its depths as well, are indeed alive.
The
acceptance of the Gaia hypothesis was, and remains, slow, halting, and
incomplete. There are several reasons for this. One is just the usual inertia,
the standard conservative reluctance to accept new ways of thinking. Yet Gaia
was also accused of being vague and shifting. Some complained that the “Gaians”
had failed to present an original, well‐defined, testable scientific proposition. How can you evaluate,
oppose, or embrace an idea that is not clearly stated, or that seems to mean
different things to different people? There was certainly some truth to this.
Gaia has been stated many different ways. Also, it didn’t help that Margulis
and Lovelock were more than willing to mix science with philosophy and poetry,
and they didn’t mind controversy; in fact, I’d say they enjoyed and courted it.
The
truth is, despite its widespread moniker, Gaia is not really a hypothesis. It’s
a perspective, an approach from within which to pursue the science of life on a
planet, a living planet, which is not the same as a planet with life on
it—that’s really the point, simple but profound. Because life is not a minor
afterthought on an already functioning Earth, but an integral part of the
planet’s evolution and behavior. Over the last few decades, the Gaians have
pretty much won the battle. The opposition never actually surrendered or
admitted defeat, but mainstream earth science has dropped its disciplinary
shields and joined forces with chemistry, climatology, theoretical biology, and
several other “‐ologies” and renamed itself “earth system science.”
The
Gaia approach, prompted by the space-age comparison of Earth with its
apparently lifeless neighbors, has led to a deepening realization of how
thoroughly altered our planet is by its inhabitants. When we compare the life
story of Earth to that of its siblings, we see that very early on in its
development, as soon as the sterilizing impact rain subsided so that life could
get a toehold, Earth started down a different path. Ever since that juncture,
life and Earth have been co-evolving in a continuing dance.
As
we’ve studied Earth with space-age tools, seen her whole from a distance,
drilled the depths of the ocean floor, and, with the magic glasses of
multispectral imaging, mapped the global biogeochemical cycles of elements,
nutrients, and energy, we’ve learned that life’s influence is more profound and
pervasive than we ever suspected.
All
this oxygen we take for granted is the byproduct of life intervening in our
planet’s geochemical cycles: harvesting solar energy to split water molecules,
keeping the hydrogen atoms and reacting them with CO2 to make organic food and body parts, but spitting the
oxygen back out. In Earth’s upper atmosphere some of this oxygen, under the
influence of ultraviolet light, is transformed into ozone, O3, which shields Earth’s surface from deadly ultraviolet, making
the land surface habitable. When it appeared, this shield allowed life to leave
the ocean and the continents to become green with forests. That’s right: It was
life that rendered the once deadly continents habitable for life.
The
more we look through a Gaian lens, the more we see that nearly every aspect of
our planet has been biologically distorted beyond recognition. Earth’s rocks
contain more than 4,000 different minerals (the crystalline molecules that make
up rocks). This is a much more varied smorgasbord of mineral types than we have
seen on any other world. Geochemists studying the mineral history of Earth have
concluded that by far the majority of these would not exist without the
presence of life on our planet. So, on Earth’s life‐altered surface, the
very rocks themselves are biological byproducts. A big leap in this mineral
diversity occurred after life oxygenated Earth’s atmosphere, leading to a
plethora of new oxidized minerals that sprinkled colorful rocks throughout
Earth’s sediments. Observed on a distant planet, such vast and varied mineral
diversity could be a sign of a living world, so this is a potential
biosignature (or Gaiasignature) we can add to the more commonly cited Lovelock
criterion of searching for atmospheric gases that have been knocked out of
equilibrium by life. In fact, minerals and life seem to have fed off each other
going all the way back to the beginning. Evidence has increased that minerals
were vital catalysts and physical substrates for the origin of life on Earth.
Is it really a huge leap, then, to regard the mineral surface of Earth as part
of a global living system, part of the body of Gaia?
What
about plate tectonics and the dynamics of Earth’s deep interior? At first
glance this seems like a giant mechanical system—a heat engine—that does not
depend upon biology, but rather (lucky for life), supports it. Also, although
we’re probably still largely ignorant about the deeply buried parts of Earth’s
biosphere, it’s unlikely there are any living organisms deeper than a couple of
miles down in the crust, where it gets too hot for organic molecules. Yet, just
as we’ve found that life’s sway has extended into the upper atmosphere,
creating the ozone layer that allowed the biosphere to envelop the continents,
more and more we see that life has also influenced these deeper subterranean
realms. Over its long life, Gaia has altered not just the skin but also the
guts of Earth, pulling carbon from the mantle and piling it on the surface in
sedimentary rocks, and sequestering massive amounts of nitrogen from the air
into ammonia stored inside the crystals of mantle rocks.
By
controlling the chemical state of the atmosphere, life has also altered the
rocks it comes into contact with, and so oxygenated the crust and mantle of
Earth. This changes the material properties of the rocks, how they bend and
break, squish, fold, and melt under various forces and conditions. All the clay
minerals produced by Earth’s biosphere soften Earth’s crust—the crust of a
lifeless planet is harder—helping to lubricate the plate tectonic engine. The
wetness of Earth seems to explain why plate tectonics has persisted on Earth
and not on its dry twin, Venus. One of the more extreme claims of the Gaia
camp, at present neither proven nor refuted, is that the influence of life over
the eons has helped Earth hold on to her life‐giving water, while Venus and Mars, lifeless through most
of their existence, lost theirs. If so, then life may indeed be responsible for
Earth’s plate tectonics. One of the original architects of plate tectonic
theory, Norm Sleep from Stanford, has become thoroughly convinced that life is
deeply implicated in the overall physical dynamics of Earth, including the
“nonliving” interior domain. In describing the cumulative, long-term influence
of life on geology, continent building, and plate tectonics, he wrote, “The net
effect is Gaian. That is, life has modified Earth to its advantage.” The more
we study Earth, the more we see this. Life has got Earth in its clutches. Earth
is a biologically modulated planet through and through. In a nontrivial way, it
is a living planet.
Now,
40 years after Viking landed on Mars, we’ve learned that planets are common,
including those similar in size to Earth and at the right distance from their
stars to allow oceans of liquid water. Also, Lovelock’s radical idea to pay
attention to the atmosphere and look for drastic departures from the expected
mixture of gases now forms the cornerstone of our life‐detection strategies.
Gaian thinking has crept into our ideas about evolution and the habitability of
exoplanets, revising notions of the “habitable zone.” We’re realizing that it
is not enough to determine basic physical properties of a planet, its size and
distance from a star, in order to determine its habitability. Life itself, once
it gets started, can make or keep a planet habitable. Perhaps, in some
instances, life can also destroy the habitability of a planet, as it almost did
on Earth during the Great Oxygenation Event (sometimes called the oxygen
catastrophe) of 2.1 billion years ago. As my colleague Colin Goldblatt, a sharp
young climate modeler from the University of Victoria, once said, “The defining
characteristic of Earth is planetary scale life. Earth teaches us that
habitability and inhabitance are inseparable.”
In
my 2003 book Lonely Planets, I described what I
call the “Living Worlds hypothesis,” which is Gaian thinking applied to
astrobiology. Perhaps life everywhere is intrinsically a planetary‐scale phenomenon with a
cosmological life span—that is, a life expectancy measured in billions of
years, the timescale that defines the lives of planets, stars, and the
universe.
Organisms
and species do not have cosmological life spans. Gaia does, and this is perhaps
a general property of living worlds. Influenced greatly by Lovelock and
Margulis, I’ve argued that we are unlikely to find surface life on a planet
that has not severely and flagrantly altered its own atmosphere. According to
this idea, a planet cannot be “slightly alive” any more than a person can (at
least not for long), and an aged planet such as Mars, if it is not obviously,
conspicuously alive like Earth, is probably completely dead. If the
little whiffs of methane recently reported by the Curiosity rover turn out to
be the signs of pockets of Martian life on an otherwise generally dead world,
this would prove that my Living Worlds hypothesis is wrong, and that life can
take on very non-Gaia-like forms elsewhere. But a living world may require more
than temporary little pockets of water and energy as surely exist underground
on Mars. It may require continuous and vigorous internally driven geological
activity. I believe that only a planet that is “alive” in the geological sense
is likely to be “alive” in the biological sense. Without plate tectonics,
without deep, robust global biogeochemical cycles which life could feed off
and, eventually, entrain itself within, life may never have been able to
establish itself as a permanent feature of Mars, as it did on Earth.
As
far as we can tell, around the time when life was starting on Earth, both Venus
and Mars shared the same characteristics that enabled life to get going here:
They were wet, they were rocky, they had thick atmospheres and vigorous
geologic activity. Comparative planetology seems to be telling us that the
conditions needed for the origin of life might be the norm for rocky worlds.
One real possibility is that Mars or Venus also had an origin of life, but that
life did not stick, couldn’t persist, on either of these worlds. It was not
able to take root and become embedded as a permanent planetary feature, as it
did on Earth. This may be a common outcome: planets that have an origin of
life, perhaps even several, but that never develop a robust and self‐sustaining global
biosphere. What is really rare and unusual about Earth is that beneficial
conditions for life have persisted over billions of years. This may have been
more than luck.
When
we stop thinking of planets as merely objects or places where living beings may
or may not be present, but rather as themselves living or nonliving entities,
it can color the way we think about the origin of life. Perhaps life is
something that happens not on a planet
but to a planet: It is something that a planet
becomes.
Think
of life as analogous to a fire. If you’ve ever tried to start a campfire, you
know it’s easy to ignite some sparks and a little flicker of flame, but then
it’s hard to keep these initial flames going. At first you have to tend to the
fire, blowing until you’re faint, to supply more oxygen, or it will just die
out. That’s always the tricky part: keeping it burning before it has really
caught on. Then it reaches a critical point, where the fire is really roaring.
It’s got a bed of hot coals and its heat is generating its own circulation
pattern, sucking in oxygen, fanning its own flames. At that point it becomes
self-sustaining, and you can go grab a beer and watch for shooting stars.
I
wonder if the first life on a planet isn’t like those first sparks and those
unsteady little flames. The earliest stages of life may be extremely
vulnerable, and there may be a point where, once life becomes a planetary
phenomenon, enmeshed in the global flows that support and fuel it, it feeds
back on itself and becomes more like a self‐sustaining fire, one that not only draws in its own air supply,
but turns itself over and replenishes its own fuel. A mature biosphere seems to
create the conditions for life to continue and flourish.
A
“living worlds” perspective implies that after billions of years, life will
either be absent from a planet or, as on Earth, have thoroughly taken over and
become an integral part of all global processes. Signs of life will be
everywhere. Once life has taken hold of a planet, once it has become a
planetary‐scale entity (a global
organism, if you will), it may be very hard to kill. Certainly life has seen
Earth through many huge changes, some quite traumatic. Life here is remarkably
robust and persistent. It seems to have a kind of immortality. Call it quasi‐immortality, because
the planet won’t be around forever, and it may not be habitable for its entire
lifetime. Individuals are here for but an instant. Whole species come and go,
usually in timescales barely long enough to get the planet’s attention. Yet
life as a whole persists. This gives us a different way to think about
ourselves. The scientific revolution has revealed us, as individuals, to be
incredibly tiny and ephemeral, and our entire existence, not just as
individuals but even as a species, to be brief and insubstantial against the
larger temporal backdrop of cosmic evolution. If, however, we choose to
identify with the biosphere, then we, Gaia, have been here for quite some time,
for perhaps 3 billion years in a universe that seems to be about 13 billion
years old. We’ve been alive for a quarter of all time. That’s something.
The
origin of life on Earth was not just the beginning of the evolution of species,
the fount of diversity that eventually begat algae blooms, aspen groves, barrier
reefs, walrus huddles, and gorilla troops. From a planetary evolution
perspective, this development was a major branching point that opened up a
gateway to a fundamentally different future. Then, when life went global, and
went deep, planet Earth headed irreversibly down the path not taken by its
siblings.
Now,
very recently, out of this biologically altered Earth, another kind of change
has suddenly emerged and is rewriting the rules of planetary evolution. On the
nightside of Earth, the lights are switching on, indicating that something new
is happening and someone new is home. Has another gateway opened? Could the
planet be at a new branching point?
The
view from space sheds light on the multitude of rapid changes inscribed on our
planet by our industrial society. The orbital technology enabling this
observation is itself one of the strange and striking aspects of the transition
now gripping Earth. If up to now the defining characteristic of Earth has been
planetary‐scale life, then what
about these planetary‐scale lights? Might this spreading, luminous net be part of a
new defining characteristic?
David Grinspoon is a senior scientist at the Planetary
Science Institute. He serves on the science teams for several active and
proposed interplanetary spacecraft missions. In 2013 he was appointed as the
inaugural chair of astrobiology at the U.S. Library of Congress. His latest
book, Earth in Human Hands, was published in 2016. Also a
musician, he plays guitar for the House Band of the Universe. He tweets @DrFunkySpoon.
From the book Earth in Human Hands by David Grinspoon. Copyright © 2016 by David Grinspoon. Reprinted
by permission of Grand Central Publishing, New York, NY. All rights reserved.
This article was originally published on Nautilus Cosmos in December 2016.
