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Intelligent Life |
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Where Does Intelligent Life Come From?
A lot of things had to go well for life to come about. If you go way back,
it all begins with a Big Bang universe giving birth to space and time. In
that early universe light echoed about, slowed in vibrancy, the primordial
elements coalesced then condensed into a first generation of massive breeder
stars. After warming to the notion (by gravitational compression),
primordial matter began fusing in stellar cores and a lesser form of light
moved outward to warm and illuminate a young and potentially ever-expanding
Universe.
More time and more space saw many of those early blue stars implode (after
living very short lives). Subsequent explosions spewed vast quantities of
heavier - non-primordial - atoms into space. Out of this rich cosmic
endowment new stars formed - many with planetary attendants. Because such
second and third generation suns are less massive than their progenitors,
they burn slower, cooler, and much, much longer - something essential to the
kind of benignly consistent energy levels needed to make organic life
possible.
Although breeder stars formed within a few hundred million years of the Big
Bang, life here on Earth took its time. Our Sun - a third generation star of
modest mass - formed some nine-billion years later. Life-forms developed a
little more than one billion years after that. As this occurred, molecules
combined to form organic compounds which - under suitable conditions -
joined together as amino acids, proteins, and cells. During all this one
layer of complexity was added to another and creatures became ever more
perceptive of the world around them. Eventually - after more billions of
years - vision developed. And vision - added to an subjective sense of
awareness - made it possible for the Universe to look back at itself.
Empirical research into the fundamentals of life shows that a concoction of
well-chosen elements (hydrogen, carbon, oxygen, & nitrogen) exposed to
non-ionizing ultraviolet radiation forms amino acids. Amino acids themselves
have a remarkable capacity to chain together into proteins. And proteins
have a rather "protean" ability to give shape and behavior to cells. It is
now considered entirely possible that the very first amino acids took form
in space1 - shielded from harder forms of radiation within vast clouds
comprised of primordial and star-stuff material. For this reason, life may
be an ubiquitous phenomenon simply awaiting only certain favorable
conditions to take root and grow into a wide variety of forms.
Currently, exobiologists believe that liquid water is essential to the
formation and multiplication of organic life. Water is an extraordinary
substance. As a mild solvent, water enables other molecules to dissociate
and mix. Meanwhile it is very stable and is transparent to visible light -
something useful if biotics are to derive energy directly from sunlight.
Finally water holds temperature well, carries off excess heat through
vaporization, and floats when cooled to solidify as ice.
According to NASA exobiologist Andrew Pohorille, "Water brings organic
molecules together and permits organization into structures that ultimately
became cells." In so doing, water acts in an unparalleled matrix enabling
organic molecules to form self-organizing structures. Andrew cites one
property uniquely associated with water that makes self-organization and
growth possible: "The hydrophobic effect is responsible for the fact that
water and oil don't mix, soaps and detergents 'capture' oily dirt during
washing in water and for a vast number of other phenomena. More generally,
hydrophobic effect is responsible for segregating nonpolar (oily) molecules
or parts of molecules from water, so they can stick together even though
they are not bonded. In biology these are precisely the interactions
responsible for the formation of membranous cell walls and for folding
proteins into functional structures."
For water to take the liquid state, it must remain in a relatively narrow
range of temperatures and pressures. Because of this only a certain few
well-placed planets - and possibly a handful of large moons are favored with
the conditions needed to let life live. In many cases it all comes down to a
form of celestial real estate - location, location, location...
Early life on Earth was very simple in form and behavior. Though cellular,
they lacked a central nucleus (prokaryotic) and other sub-structures
(organelles). Lacking a nucleus such cells reproduced asexually. These
anaerobes subsisted primarily by creating (anabolizing) methane gas from
hydrogen and carbon-dioxide. They liked heat - and there was plenty of it to
go around!
The fact that life developed on Earth should not be as surprising as one
might think. Life is now considered far more robust than once imagined. Even
now hydrothermal vents deep in the ocean eject near-boiling water. Adjacent
to such vents life - in the form of giant tube worms and clams - flourishes.
Deep under the surface of the Earth mineral-metabolizing anaerobic bacteria
are found. Such conditions were thought impossible throughout most of the
20th century. Life seems to spring up under even the harshest of conditions.
As life forms advanced on our world, cells developed organelles - some by
incorporating lesser, more specialized cells into their structures. The
planet cooled, its atmosphere clarified and sunlight played upon the oceans.
Primitive bacteria arose that fixed energy from sunlight as food. Some
remained prokaryotic while others developed a nucleus (eukaryotic). These
primitive bacteria increased the oxygen content of the Earth's atmosphere.
All this transpired some 2 billion years ago and was essential to support
the quality and quantity of life currently populating "the Blue Planet".
Originally the atmosphere consisted of less than 1% oxygen - but as levels
increased, bacteria-eating life-forms adapted to synthesize water from
oxygen and hydrogen. This released far more energy than methane metabolism
is capable of. The controlled synthesis of water was a huge accomplishment
for life. Consider the high school chemistry lab experiments where hydrogen
and oxygen gas are combined, heated then explode. Primitive life forms had
to learn to handle this very volatile stuff in a far safer manner - putting
phosphorus to task in the conversion of ADP to ATP and back again.
Later - roughly 1 billion years ago - the simplest multi-cellular creatures
took form. This occurred as cells came together for the common good. But
such creatures were simple colonies. Each cell was fully self-contained and
took care of its own needs. All they required was constant exposure to the
warm broth of the early oceans to acquire nutrients and eliminate wastes.
The next great step in the evolution of life2
came as specialized cell tissue types developed. Muscle, nerve, epidermis
and cartilage advanced the development of the many complex life-forms now
populating our planet - from flowering plant to budding young astronomer!
But that very first organized creature may very well have been a worm
(annelid) burrowing through the marine slime of some 700 million years ago.
Lacking eyes and a central nervous system it possessed only the capacity to
touch and to taste. But now life had the capacity to differentiate and
specialize. The creature itself became the ocean...
With the advent of well-organized creatures the pace of life quickened:
By 500 MYA, the first vertebrates evolved. These were probably eel-like
creatures lacking in sight but sensitive to chemical - and possibly
electrical - changes in their environments.
By 450 MYA, the first animals (insects) joined rooting plants on land.
Some 400 MYA the first vertebrates climbed out of the sea. This may have
been an amphibious fish subsisting on insects and plant-life along the
shore.
By 350 MYA - the first "iguana-like" reptiles emerged. These possessed
strong, hard, jaws in a one-piece skull. As they grew larger, such reptiles
lightened their skulls by adding orifices (beyond simple eye sockets).
Before dinosaurs dominated the earth, crocodiles, turtles, and pterasaurs
(flying reptiles) preceded them.
Primitive mammals go back almost 220MY. Most of these creatures were small
and rodent-like. Later versions developed the placenta - but earlier species
simply hatched eggs internally. All mammals of course, are warm-blooded and
because of this must eat voraciously to maintain body temperature -
especially on cold windy nights tracking down faint galaxies along the
Eridanus river...
Like mammals, warm-blooded birds require more food than reptiles - but like
reptiles - laid eggs. Not a bad idea for a creature of flight! Today
celestial birds fly (such as late summer's Cygnus the Swan and Aquila the
Eagle) because real birds took wing some 150 MYA.
The earliest primates existed even during the time of the extinction of the
dinosaurs Strong evidence supports the idea that the dinosaurs themselves
passed as a group after an asteroid - or comet - impacted the Yucatan
peninsula of the United States of Mexico. After this catastrophic event
temperatures fell as a "non-nuclear" winter descended. Under such conditions
food was spare, but warm-bloodedness came into its own. It wasn’t long
however before one type of a "gigantism" soon replaced another - mammals
themselves grew to extraordinary sizes and the largest developed in the womb
of the sea and now take the form of the great whales.
The end of the "terrible lizards" was not the first mass-extinction of life
- four previous die-offs had preceded it. Today, aware of the potential for
other such cataclysmic impacts, some of the world's astronomers keep an eye
on near-earth orbiting chunks of debris left over from the formation of the
solar system. The smallest types - meteors for instance - put on harmless
celestial light shows. Larger meteors (bolides) occasionally spread "flame"
and trail "smoke" as they crash to Earth. Larger bodies have left wakes of
natural devastation across miles of forests - without even leaving a trace
of their own "party crashing" material behind. But larger intruders have
little such modesty. An asteroid or comet one kilometer in diameter would
spell absolute calamity for a population center. Bodies ten times that size
may account for massive die-offs of the type that spelled the end of the
dinosauria.
Human beings first walked upright some 6MYA. This probably occurred as the
path diverged between proto-chimpanzees and early hominids. That divergence
followed a ten million year period of rapid primate evolution and blended
into a six-million year cycle of human evolution. The first stone tools were
crafted by human hand roughly 2 million years ago. Fire was harnessed by
some enterprising member of the human species a million years later.
Technology gained momentum very slowly - hundreds of thousands of years have
passed without any significant improvement in the tools used by the tribal
societies of long past.
Modern humans originated more than 200,000 years ago. Some 125 thousand
years later an event occurred that may have reduced the entire human
population of planet Earth to less than 10,000 individuals. That event was
not extra-terrestrial in nature - the Earth itself probably belched forth
"fire and brimstone" during the eruption of a gas-charged magma chamber
(similar to that beneath Yellowstone National Park in the western USA).
Another 65,000 years passed and the stone age gave way to the age of
agriculture. By 5000 years ago the first city-states coalesced within
fertile valleys surrounded by far less hospitable climes. Whole
civilizations have come and gone. Each passing a torch of culture and slowly
evolving technology to the next. Today it has been only a few short
centuries since the first human hand shaped lenses of glass and turned the
human eye upon the things of the Night Sky.
Today huge mirrors and space probes allow us to contemplate the vast reaches
of the universe. We see a Cosmos dynamic and quite possibly thrilling with
life more abundant than anyone could possibly imagine. Like light and
matter, life may very well be a fundamental quality of the space-time
continuum. Life could be as universal as gravitation - and as personal as an
evening alone with a telescope beneath the night sky...
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1 In fact, the radio-frequency spectrographic fingerprint of at least one
amino acid (glycine) has been found in vast clouds of dust and gas within
the interstellar medium (ISM). (See Amino acid found in deep space).
2 That life develops from less sophisticated to more sophisticated forms is
a question beyond scientific dispute. Precisely how this process takes place
is an issue of deep division in human society. Astronomers - unlike
biologists - are not required to hold any particular theory on this issue.
Whether chance mutation and natural selection drives the process or some
unseen "hand" exists to bring such things about is outside the realm of
astronomical inquiry. Astronomers are interested in structures, conditions,
and processes in the universe at large. As life becomes more salient to that
discussion, astronomy - in particular exobiology - will have more to say
about the matter. But the very fact that astronomers can allow nature to
speak on such issues as a sudden and instantaneous "creation ex nihilo" in
the form of a Big Bang shows just how flexible astronomical thinking is in
regard to ultimate origins.
Acknowledgment: My thanks goes out to exobiologist
Andrew Pohorille of NASA who enlightened me as to the great significance of
the hydrophobic effect on the formation of self-organizing structures. For
more information on exobiology please see NASA's Exobiology Life Through
Space and Time official website through which I had the good fortune of
contacting Andrew.
About The Author:
Inspired by the early 1900's masterpiece: "The Sky Through Three, Four, and
Five Inch Telescopes", Jeff Barbour got a start in astronomy and space
science at the age of seven. Currently Jeff devotes much of his time
observing the heavens and maintaining the website
Astro.Geekjoy.
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Copyright © 1999-2004 Universe Today, All rights reserved.
http://www.universetoday.com
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