by Bruce Behrhorst
The
origin of life has remained unsolved in science.
No one can know how, where or when life originated. The only evidence known
for certain is that microbial life had established itself on Earth by about 3.5
billion years ago. What came before remains even more of a mystery. Thirty years
ago the prevailing idea among biologist was that life resulted from a chemical
fluke and unlikely to happen again in the observable universe. This conservative
opinion was exemplified by noble prize winner French biologist, Jacques Monod
 “Man
at last knows that he is alone in the unfeeling immensity of the universe, out
of which he emerged only by chance.” Recently has this idea been supplanted in
1995 by Belgian Biochemist Christian de Duve called life “A cosmic imperative”,
“It is almost bound to arise on any Earth-like planet.
Among astrobiologists the universe is teeming with life.
How can scientist determine which view is correct?
The most direct way is to seek evidence for life on another
planet such as Mars or moons around our solar system gas giants
(Jupiter and Saturn). If life originated from scratch on two
planets in a single solar system, it would decisively confirm
the hypothesis of biological determinism. Unfortunately in
current public discourse an apathetic public and war
expenditures heralds space exploration as a low priority issue.
Can we view a value to space exploration other than the typical
aspirations such as national prestige to increasing space
venture investment?
Questions like: How does life begin and evolve? Does life exist
elsewhere in the universe? What is the future of life on Earth
and beyond?
Determining life forms that may exist elsewhere in our solar
system which one day could prove useful in combating diseases
like cancer for humans on Earth.
One thing is for certain humans can only be found in our solar system. Human
beings are very distinct in our galaxy. It would be almost an impossibility at
finding another organism exactly like it with the same level of molecular
genetics - the human fingerprint once imprinted is never duplicated. On earth
even with human intervention and manipulation the human genome would revert to a
natural environmental default setting if left undisturbed. Likewise humans can
change and adapt to any extraterrestrial environment that allows it to exist and
flourished.
Some authors have called the discovery of DNA by Watson & Crick as the
greatest single scientific achievement in human history. Slightly overstated, it
doesn’t account for other equally important discoveries in physics; relativity,
quantum mechanics, cosmology etc. All these sciences contribute to our
understanding of the universe as space science continues to evolve. By at least
the year 2050 it would be surprising if we hadn’t yet understood how life began
on Earth.
ARE WE ALL ALONE
The most intrigue is in the exploratory challenges of the
next fifty or so years to seek evidence for or against the
existence of extraterrestrial sentient life. We would then, with
direct extraterrestrial evidence, be able to access how likely
it was that life in some basic form had emerged on some other
moon or planet. Of course this leaves open a harder second
question: If simple life had emerged what are the odds against
it evolving into something that we could recognize as
intelligent?
Already space probe rovers such as the Spirit & Endeavour
Rovers, the future Phoenix and the Mars Science Lab (MSL)
nuclear powered rover missions to Mars designed to study the
Martian surface and possibly to return samples to Earth. They
have left no doubt liquid water once flowed on its surface. If
by chance the present and future Mars instruments reveals that
even the most rudimentary life form originated independently at
this location within our solar system, it would imply that
simple life must be wide spread in the galaxy and beyond. Nobody
now expects “advanced” life anywhere else in our solar system,
but our star Sun is just one average star among billions in the
Milky Way. Could planets orbiting other stars, Alpha Centauri
our neighboring three star stellar system (4.22 light-years
away) could be a candidate for terrestrial planets that harbor
life-forms more interesting and exotic than anything we might
find on Mars? Could they even be inhabited by beings recognized
as intelligent? Even if primitive life is common throughout the
universe, the chances of advanced life might not exist. We just
don’t have enough space explorative information on life’s
origins and still less about whether natural selection is
“convergent” or would yield a quite different outcome if the
organism were allowed to re-run on Earth to say whether
intelligent aliens are likely or unlikely.
These questions might not translate to well with commercial
space operation aspects. This type of space science is not a
high priority, if anything it would be an incidental
extraterrestrial life find unlike a government project specific
to the task of funding missions for the sole purpose of
exploration and finding evidence. If life exists extra
terrestrially commercial space operations could also contribute
to an important discovery akin to a commercial concern hiring a
construction or tunneling contractor who’s diggings unearth a
surprising paleontological and archaeological site who’s
discovery may not have been made had it not been for the
commercial concern working at the site of the find.
The SETI Institute in California is an example of an
organization finding it hard to justify commercial existence
still SETI continues to attract hefty donations in part from
well-heeled visionary benefactors. It seems a stretch to imagine
an alien communication would ever reach human operators and
their equipment. The odds are heavily weighted against success
in receiving the artificial signal even something like a string
of prime numbers, we would not know, of course, whether the
transmission came from anything ‘conscious’ or an artifact left
by a species that had been extinct long before the message
transmitted arrived to our receiver dish. Such scanning searches
maybe doomed to fail. This would be viewed as some sort of
failure. But it need not be implied that other intelligent life
not exist-they could be leading contemplative lives choosing not
to make their presence felt. Another angle would describe our
cosmic self-esteem having been lifted knowing we were indeed a
unique abode of intelligence: The justification of view in a
less humble cosmic perspective than it would merit if our galaxy
teemed with complex life. We would regard Earth as a “seed” from
which life would be broadcasted throughout space.
There is plenty of time ahead. Assuming some degree of
celestial stability when you compare timelines in space & time.
The galaxy across extends about 100,000 light-years and it could
be greened in less time than it took us to evolve from the first
primates. The sun wanes, 5 billion more years will elapse;
that’s 5 times longer than it has taken for natural selection to
lead from the first multicellular organism to Earth’s present
biosphere including us. During those eons of time, there could
be even larger qualitative leaps. Future changes could indeed be
much faster if artificially directed, so that they occur on a
cultural or historical timetable.
We can’t predict what role life will eventually carve out for
itself.
Life as we know it could be ‘snuffed out’, extinct instantly
by natural, violent aliens or self induced termination. Or it
could achieve such dominance that it would influence the entire
cosmos. This might sound absurd but the possibility can’t be
discounted either-only God knows for sure.
By contrast, Earth may not have been habitable until about 3.9 billion years
ago. Both Mars and Earth are subjected to a violent bombardment by giant
asteroids and comets for at least 700 million years after the formation of the
solar system 4.5 billion years ago. Some of the biggest impact events would have
been so violent that they would have sterilized the entire planet; enshrouding
rock vapor at a temperature of 3,000 degrees a global kiln at such a heat pulse
would have sterilized (killed) anything that wasn’t below at least a kilometer
in the ground. But no organism would have settled at very great depths because
it would be too hot to live there. There must have been a comfort zone, bordered
below by the internal heat of the planet and above by heat pulses from major
impacts. On Mars this comfort zone for deep-living microbes would have been
deeper sooner, making favorable odds that life there had established itself
early. On earth all life is inter related-it is descended from a common
ancestor. The varieties of species inhabiting our biosphere are just different
branches on a universal tree trunk of life.
If life did start on Mars and spread to Earth, then a relic Martian life form
would represent just another branch on this tree-maybe a lower older branch but
one sharing a common origin. With terrestrial life. By at least year 2050 gene
sequencing techniques will have been automated and equipment transportable. It
could be quite possible to carry out the analysis on the Martian base, removing
the need for quarantining procedures.
If Martian life turned out to be the same as terrestrial life, then Mars will
have failed to provide the second sample of life we seek. It might be possible
still to confirm that the origin of life was a freak accident. Unique in the
universe. The matter of life’s uniqueness or ubiquity we would need to look
farther away in our solar system. The only other body in the solar system
suspected of substantial quantities of liquid water is Europa. A moon of Jupiter
with its icy crust beneath which probably lies a liquid ocean, warmed by tidal
friction as Europa orbits Jupiter. Europa being so distant from earth it would
be very unlikely to have been biologically contaminated by Earth or Mars.
Unfortunately since all the worlds’ space agencies have a poor record of
continuous human space exploration capacity sending a crewed expedition to
Europa; even in the next 50 years is not likely. However an unmanned probe would
be likely be sent there in the next thirty years maybe the restart of the
Jupiter Icy Moons Orbiter (JIMO) mission might be relevant. Astrobiologists
agree there is scant chance of finding any type of extraterrestrial life in the
solar system more advance than the simple single cell bacteria complex life
forms might need a planet very much like Earth, with thick atmosphere, liquid
water, an ozone layer and plate tectonics to recycle atmospheric gases like CO2.
NARROWING CRITERIA FOR
EXTRATERRESTRIAL LIFE
Analogous to a police ‘line up’ of suspects where a witness
to a crime attempts to reveal the perpetrator to police.
Scientists like police investigate celestial bodies in a
‘line-up’ of suspected exoplanets or moons harboring life.
Astrobiology scientists have expanded a list of different types
of earth-sized planets and where they might be found. They have
models for 14 different types of solid planets that might exist
in our galaxy.
Of special interest are the so-called solid ‘rocky’ planets
silicate (like earth) and carbon composition of diameter and
mass as earth. It is thought more likely to be likely habitats
for life than their gas-giant relatives.
Some are pure water ice, carbon, iron, silicate, carbon monoxide and silicon
carbide and others are mixtures of the various compounds.
As with any planet suspected of harboring life the prime factor is the health
and condition of the ultimate life provider the stellar ‘caregiver’ be it a
single or double star system. Young stars with protoplanetary disks scientist
believe our moon arose about 30 to 50 million years after our sun was born since
astronomers observe the planet-building process itself winds down. Like our
moon, rocky planets are built up through messy collisions that spray dust all
around. Scientists have calculated how gravity would compress down. The computer
models result predict a planet’s diameter for a given composition and mass. For
example, a one-earth-mass planet made of pure water will be about 9,500 miles
across, whereas an iron planet with the same mass will be only 3,000 miles in
diameter. To compare earth is a mostly silicate planet and is 7,926 miles across
at the equator. Scientist have discovered that no matter what material a planet
is made of the mass/diameter relationship follows a similar pattern. All
material will compress in a similar way because of the structure of solids, “If
you squeeze a rock, nothing much happens until you reach some critical pressure.
Then it crushes. Planets behave the same way, but react at different pressures
depending on composition. The astrobiologist team hopes these models will yield
insights into planet compositions when astronomers start finding earth-sized
planets around other stars. Missions like the French COROT satellite and Kepler
spacecraft. COROT launched in 12/27/06 and NASA Kepler spacecraft launches in
2009 can find planets not much larger than earth by watching them pass in front
of their host star, events known as transits. But astronomers caution it would
still be difficult to distinguish between a silicate planet from a carbon
planet. Since they’re about the same size for given mass. In order to make the
finer distinction you would need help from the James Webb space telescope or
terrestrial planet finder.
SPACE VENTURE DISCOVERY OF EARTH’S
TWIN
With the exception of Pulsar planets, all of the extrasolar
planets detected so far are gas giants approximately 150 as of
2005. The challenge now is to find terrestrial planets habitable
planets like Earth, which are 300 to 600 times less massive than
Jupiter. The Kepler Mission spacecraft is a gigantic light-meter
used to determine changes in a suspect planet harboring star’s
brightness of about 1/10,000, 100 parts per million (ppm)
lasting for about 2-16 hours as the planet transits (passes in
front of its star) the stars brightness is altered temporarily.
The hope is to essentially process enough stars and narrow from
a list of candidate extrasolar earth-like planets that when
subjected to further analysis might expose a planet harbouring
life forms.
Kepler objectives are:
-Determine the percentage of
terrestrial and larger planets there are in or near the
habitable zone of a wide variety of stars.
-Determine the distribution size and shapes of the planets
orbits.
-Estimate how many planets there are in multiple-star
systems.
-Determine the properties of those stars that harbour
planetary systems.
The hope is to provide enough data for future missions like the Space
Interferometry Mission (SIM) and the Terrestrial Planet Finder (TPF) to
pinpoint planets that contain life forms. It's only been
during the past decade that dramatic progress has been made in the
understanding of the potential for past and present habitable
environments elsewhere in the solar system.
For example, Mars Global Surveyor, Mars exploration
rovers, the Odyssey and Mars reconnaissance orbiters reveal early
in Mars history surface water environment was widespread over the
surface. Present theory and surface geomorphology point to potential for
global ground water system capable of sustaining subsurface biosphere,
the recent discovery of atmospheric methane indicates a habitable
environment presently on Mars.
The Galileo mission found strong evidence of subsurface brines on three
of the four Galilean satellites of Jupiter (Europa, Ganymede and
Callisto) maintained by internal tidal heating. The Cassini-Huygens
mission has confirmed the presence on Saturn's moon, Titan of an
atmosphere and a surface rich in pre-biotic organic compounds. The
existence of lakes of liquid hydrocarbons on Titan open up the
possibility for solvents and energy sources that are alternatives to
those in our biosphere and might support a different life form than
those from earth. The Cassini spacecraft has imaged plumes of water that
erupt periodically from the subsurface of Enceladus an icy moon of
Saturn. This indicates some possibility interior has habitable zones
with liquid water might exist on yet another body in our solar system.
Key questions are always asked. If life ever arose elsewhere is it
related to terrestrial life, or did other bodies in the solar system
sustain independent origins of life? And if life never developed
elsewhere in our solar system, is there some sort of prebiotic record
preserved in ancient rock that might contain clues about how life began
on earth? FEATURE INTERVIEW
In an effort to answer some of these intriguing questions on postulates
of a 'Universal Biology' and how for example an ancient earth some 4.3
billion years ago might have developed sources of prebiotic material and
catalysts.
I contacted Zach Adam who researches life's origins at the department of
Aeronautics/Astronautics Engineering and the Center for Astrobiology at
the University of Washington, Seattle, Washington. He points to an
unusual explanation involving nuclear science and its chemistry.
According to Mr. Adam, life began in a radioactive beach environment. In
a geologic framework the origins or the precursor conditioning in
support of life in the Hadean era the first point in the earth's
existence timeline put a heavy mineral beach developed unique chemical
properties of low-electronic actinides, which act as nuclear fissile and
fertile fuel, radiolytic energy sources, oligomers catalysts and
coordinating ions along with mineralogy associated with Lanthanides to
form prototypical prebiotic homonuclear and dinuclear metalloenzymes. He
built a four-factor nuclear reactor model to estimate how much Uranium
would have been required to initiate a sustainable fission reaction
within the ancient beach sand 4.3 billion years ago. He calculates about
1-8 wt.% of sand would have to have been Uraninite depending on the
weight percent, uranium enrichment, and quantity of neutron poisons
present within the remaining minerals.
His radiolysis experiment were conducted with various solvents with the
use of Uranium and Thorium-rich minerals (metatorbernite and Monazite
respectively as proxies for radioactive beach sand in contact with
different carbon, hydrogen, oxygen and nitrogen reactants. Radiation
bombardment ranged in duration of exposure from 3 weeks to 6 months. Low
levels of Acetonitrite (estimate to be in the order of parts per billion
(PPB) in concentration were conclusively identified in 2 setups and
tentatively indicated in a 3rd by gas chromatograph/mass spectrometry.
These low levels are interpreted within the context of a Hadean beach
framework to demonstrate promise in investigating natural nuclear
reactors as power production sites that might have assisted the origins
of life on young rocky planets with a sufficiently differentiated
crust/mantle structure. NATURAL REACTORS:
Mr. Adams notes, there is still a debate over the history of the
continental crust formation and its far from resolved, it's clear that a
young earth was much more geologically complex than has been previously
assumed. If earth's crust/mantle system was sufficiently differentiated
at a young age and moon had coalesced into a single body, then it's
possible natural nuclear reactors could have formed under paleoclimate
constraints much different than those that formed the only verified
instance of natural nuclear reactors on earth. The most studied site is
in Gabon, Africa called the "Oklo
deposits" is were since 1970's when extensive uranium mining
operations were conducted that samples sent from Gabon to France for
analysis revealed that some uranium sample were consistently depleted in
U235, After ruling out contamination with depleted tailings,
investigators traced the depletion to the Oklo deposits. this
demonstrated that up to six natural reactors were responsible for
depletion of the U235 fuel sufficient enough to generate 100kw each. The
genesis of natural reactors is widely believed to have been unique to
a period of time from 2.4-1.9 Ga (billion years ago).
Bruce:
"The origin of life has remained unsolved in science.
No one can know how, where or when life originated.
The only evidence known for certain is that microbial life had
established itself on Earth by about 3.5 billion years ago. What came
before remains even more of a mystery. In challenging the current idea
that phosphate was later integrated into biotic process.
You state the possibility that phosphorus was present in the very first
chemical systems of protypical life due to mineralogical and geophysical
association with actinides and that the release and activation of this
phosphorus was an atypical feature of prebiotic energy transfer
mechanisms as compared to contemporary
analog settings. What do you mean by compared to contemporary analog
settings?
Zach:
All of your statements are true, however, the unbelievable increase in
our understanding of the role of DNA, RNA, the structure and composition
of enzymes, and the properties of cell walls and what makes life able to
function means we can frame the question 'Where did Earth life come
from, and how might it arise on other planets?' in more and more
specific ways.
As humans, we're not known to shy away from unanswerable questions, but
to take an unanswerable question and investigate the essence of the
question makes it unanswerable. Sometimes we get lucky and simply find
out we were asking the wrong, unanswerable question all along. In other
words, asking where Earth life came from is not pointless, if only
because increasing our understanding may show us the path to propagating
life of all shapes and sizes throughout the solar system.
If you look at the logistics, space access is important but it is only
one part of a multifaceted 'bottleneck' that is keeping humans on Earth
- at least part of the 'bottleneck' is understanding how an ecosystem
can be driven to grow from a small origin, in a harsh environment, with
little resources, to produce a stable, robust, and independent
ecosystem. If we understood this process better, we wouldn't need so
many rocket launches to build bases on Mars, as an example.
Regarding your specific question about contemporary analogs, I meant
contemporary radioactive beaches. Yes, they exist but they are nowhere
close to being fissionable because U235 has decayed so much more quickly
than U238. And even in cases where there are phosphates (such as
monazite beaches) the monazite is simply not bombarded with enough
energy to cause decomposition of the monazite before the beach itself is
washed away. So the phosphate doesn't even get a chance to be liberated
and activated in the modern world, and in any case, life scavenges
phosphorus so efficiently that it doesn't really need mineral forms of
phosphorus in most places.
Bruce:
"You mention ancient Oklo site nuke reactors. (2 Ga) on Earth.
Is there a possibility that similar 'natural' reactors also exist in our
solar system on (Triton, Enceladus, Mars, Venus, Europa etc.)?"
Zach:
I can't answer this with any certainty since our assessment of the solar
system is rudimentary at best. Needless to say, I would be thrilled to
find one. But my gut feeling is that we won't find any currently active
ones, if only because presumably most of the material in our solar
system came from the same condensed dust cloud that produced the Earth.
And the Uranium in that cloud has pretty much decayed away all but a
small percent of the fissionable 235U or Pu that might have been present
at the time the planets formed.
Bruce:
"Radiation hormesis is the hypothesis that ionizing radiation is benign
at low levels of exposure, and that doses at the level of natural
background radiation can be beneficial.
Is it possible that living organisms of today (humans) have a certain
level of tolerance to radiation; High mountain altitude communities,
thorium beaches of Florida, Brazil, India etc. regions of natural
radiation exposure?"
Zach:
I've heard of this idea, but I am not trained in radiation medicine or
specific consequences of radiation exposure. I can say, however, that
our understanding of mortality limits and interdependencies between life
and radiation, especially at the microbial level, has expanded
dramatically since Astrobiology began asking these kinds of questions.
We are finding microbes in African mines and beneath Canadian permafrost
living in water that, for all intents and purposes, hasn't had any
interaction with the surface biosphere for at least the last thousands
of years, which apparently feed off of the radiolysis of water as an
energy source quite happily (look up the work of TC Onstott, for
examples). We are finding microbes that have self-repairing capabilities
that enable them to live at radiation levels that would kill humans in
minutes (the species is known as Deinococcus radiodurans, and I suggest
reading about these remarkable organisms). The bottom line is that
microbes are much tougher than we are, and we could really use their
help in making other planets such as Mars habitable for humans by
assimilating materials in the Martian environment into their cells, from
which plants and scavengers could feed, from which humans could feed.
It's better than packing a century's worth of granola bars at $20,000
per lb. just to get the stuff into orbit.
Bruce:
"You describe life's origins on a rocky mass planet 1 earth dia.
Would the same rules apply to solid planets that might exist in our
galaxy?
(Of special interest are the so-called solid 'rocky' planets silicate
[earth like]
and carbon composition of diameter and mass as earth.)"
Zach:
Yes. One key aspect is the differentiation of the crust from the mantle,
as this serves to concentrate fissionable material at the surface, to
the best of our current understanding of the structure of the Earth.
Rocky planets much bigger (also known as 'Superearths') or smaller than
the Earth might even be better at concentrating actinides at the surface
in greater abundance, but we haven't visited enough such planets to know
for sure what the optimal configuration is. Finding other planets and
spotting life signatures similar to our own, which scientists hope to do
over the next few decades, would be very helpful. Mr.
Adam is working on industrial uses in recycling 'hot' spent rods from
nuclear reactors and cost effective ways of recovering spent fuel.
references:
-The Next Fifty Years: science in the first half of the twenty-first
century, edited by John Brockman
-NASA Astrobiology |