Probing the Chemistry of Creation

Scientists are studying comets, volcanoes and other planets for clues to
the origin of life on Earth. The quest is frustrating, but some say life forms
may be brewed in a lab within decades.

By ROBERT LEE HOTZ, Times Science Writer

[...]

Come, take a seat in the kitchen of creation and try to replicate the lost
recipe for the origin of life.

Be warned. This is a hypothetical dish that must be prepared through trial
and error from the raw chemistry of Earth and space--without benefit of
conventional biology or supernatural intervention.

So, experiment. Stoke the primordial planet's volcanic ovens. Stir its
ocean
caldron with wind. Boil it. Ice it. Season it with cyanide. Pepper the mix
with comet dust and leaven it with time.

That is the task facing researchers trying to reconstruct the chemistry of
creation.

To investigate the origin of life, some researchers are taking hints from
the components of today's biochemistry and trying to work backward to
discover simpler organic molecules that can perform life's essential
functions.

In recent months, a NASA consortium of scientists has been shedding new
light on the primeval biochemistry that existed before the first mating
dance of proteins and DNA, which underlies all modern biology.

The group draws together biologists, chemists and geophysicists based at
the research centers of "Biotech Beach" along the San Diego-La Jolla
coastal corridor.

Its members have helped reset the clock of evolution and uncovered the
earliest known evidence of life on Earth.

And in a crucial step with several other laboratories, other members have
created a functional imitation of a primordial living molecule--a self-
replicating substance that can be made to evolve and adapt without the
help
of DNA.

They have even evolved forms of DNA that nature did not. Last month two
consortium scientists for the first time created a primitive molecule that
can reproduce itself and evolve generation after generation in a
continuous
test-tube reaction. Some leading researchers now are confident that it may
be
only a decade or so before they can create life from scratch.

In the laboratory, however, life still requires a guiding hand.

Scientists have tried--and repeatedly failed--to create the conditions
under
which life can arise spontaneously. Nor have they been able to create a
molecule that--unaided--can reproduce itself in a self-sustaining
reaction.
No one knows when anyone may achieve that ultimate goal.

This daunting laboratory enterprise, however, has become even more
provocative as researchers eye primordial Mars and the frozen moons of
Jupiter for havens of primitive life. Astronomers also yearn for signs of
organic chemistry on any of the planets discovered recently around other
sun-like stars.

Indeed, in some theoretical scenarios, the icy wastes of Jupiter's Europa,
recently scanned by NASA's Galileo probe, bear a striking resemblance to
the alien Earth of more than 4 billion years ago. Geologists suggest that
life may exist in volcanic vents below Europa's icy crust, just as
bacteria live
in Earth's underwater volcanoes today and in lakes deep beneath the icecap
of
Antarctica.

The idea is seductive. Basic organic chemicals float in clouds of
interstellar dust. They have been detected in the tails of comets like
Hale-Bopp. And
they have been discovered in meteorites as old as the solar system.

So it may seem only natural to expect that such interstellar chemicals
seeded life on other planets. After all, life on Earth has taken up
residence in so many unexpected places. Bacteria thrive in the absence of
oxygen or
sunlight, in boiling water, perpetual ice and subterranean depths, feeding
readily on toxic wastes or on antibiotics designed to eradicate them.

But without a technical inkling of just how life arose in the one place it
is known to exist, the search for life elsewhere in the universe is based
largely on wishful thinking, researchers say.

More important for them, the effort to re-create the original chemistry of
life offers the possibility of a scientific answer to one of humanity's
most
persistent spiritual and philosophical questions: How did life begin?

Despite the daunting uncertainties, a recent series of advances has many
researchers hopeful that it may be only a matter of time before science
succeeds in creating life in the lab.

"We may never know how it happened on Earth, but I am confident that
somebody is going to do it in the laboratory within the next 10 or 20
years," said Leslie E. Orgel at the Salk Institute for Biological Studies.

Orgel, an authority on the origin of life, has joined with NASA and four
other prominent specialists--Stanley Miller at UC San Diego, Gustav
Arrhenius and Jeffrey L. Bada at the Scripps Institution of Oceanography,
and Gerald Joyce at the Scripps Research Institute--to probe this enduring
mystery.

Although they still may be far short of their goal, their growing
understanding of life's early chemistry offers the promise of powerful new
drugs based on molecules custom-tailored by directed test-tube evolution.

More important, perhaps, the work of the NASA group reinforces the raw
power of evolution as a natural force to spur change even in primitive
molecules, forcing these collections of atoms to spawn creations more
complex than themselves.

What seems most striking about this endeavor, researchers acknowledge, is
that it is almost wholly an act of scientific intuition, constrained only
by
the rules of organic chemistry.

Should they succeed, they will have no way to know if they have actually
learned how life began or if they simply invented a new prescription for
its
creation.

"If you had the correct answer to the origins of life, you would not be
able
to prove it is correct," said chemist James P. Ferris at the Rensselaer
Polytechnic Institute in Troy, N.Y., who works with Orgel.

"Our hope is to build systems that seem reasonable from what we know.
We may be way off the mark."

Molecules Jockeying for Dominance

In the beginning, life may have existed as little more than a set of
unusual
molecules with the remarkable ability to store information, copy
themselves
and change in response to conditions around them. Long before there was
even a single cell to divide and multiply, these individual molecules
jockeyed for dominance.

So, by this theory, the first living thing may have been a spreading patch
of discolored clay at the edge of a drying lagoon or a mineral-like
formation
building up on a submerged volcanic vent. There was no hint that, in time,
this self-sustaining chemical reaction would dominate the planet.

"The story [of life] has its beginning at the point...when molecules first
began to undergo Darwinian evolution," said Gerald Joyce, an expert in
molecular evolution and a senior partner in the NASA collaboration.

By attempting to understand the composition and character of these
forerunner molecules, researchers are exploring a realm that today exists
only in theory.

Certainly, researchers agree, life did not start out with the
sophisticated
biochemical machinery of DNA, which today allows the molecular
information of life to be carried inside a universal genetic code and
copied
every time a living cell divides.

But in trying to determine how DNA evolved into being, researchers must
answer a riddle. Which came first: The DNA that stores genetic
information or the proteins that enable it to copy itself?

Some researchers have sidestepped that question by conceiving a molecule
that encompasses both.

Orgel and Nobel laureate Francis Crick--the co-discoverer of DNA--
proposed that life might have started with a crucial organic molecule
called
RNA.

Today, RNA is merely a cog in the master machinery of life. It serves as
an
intermediary in the transcription of genetic information encoded in
complex
molecules of DNA, aiding in the manufacture of vital enzymes, proteins
and hormones. But once it may have functioned alone.

It is possible that RNA-based life forms evolved into the more stable
structure of DNA.

Nobel laureate Walter Gilbert dubbed this hypothetical kingdom of RNA-
based life forms the "RNA world," and evidence suggests that this theory
may be close to the truth.

"What makes it particularly tricky is that we don't ever expect to have
fossil evidence of the RNA world," said Joyce. "We don't literally expect
to ever
see direct physical evidence that the RNA world existed on this planet or
any other, for that matter."

Nonetheless, several researchers have shown that, in the laboratory, RNA
can be made to copy itself without the assistance of the genes or protein
enzymes so necessary to the function of living cells today.

Joyce and his colleagues have induced these RNA molecules to undergo
primitive evolution.

The ability to force the RNA molecules to adapt to changing conditions
bolsters the theory of the RNA world, experts said.

"It has the look and feel of what the RNA world in the test tube would
look like," Joyce said of his team's most recent experiments.

That does not say necessarily that life started with RNA. It may have only
been one of many molecular "species" that contended for resources in the
primordial pools.

Indeed, Orgel and his colleagues are investigating the possibility of
primitive protein-based molecular life, instead of more familiar RNA or
DNA.

But even such primitive forms require a certain level of complexity to
function. And evolution cannot begin without the right kind of raw
material.

"How do you start evolution without the help of evolution?" Joyce said.
"How do the chemical reactions bootstrap themselves to the magic moment
when . . . evolution begins?"

Life Amid Rubble of Young Solar System

Whatever its original form, life on the embryonic Earth arose earlier and
perhaps faster than anyone had imagined, researchers at the Scripps
Institution of Oceanography recently determined.

New chemical evidence from the planet's oldest known sedimentary rocks
suggests that life was thriving 3.8 billion years ago, dangerously close
to--or even during--the eons when the infant planet was bombarded by the
rubble left over from the formation of the solar system.

It may have taken 10 million years or less to go from a primordial soup of
inanimate organic chemicals to the first bacteria whose remains form those
earliest known fossils, researchers say. This is far faster than the
billions of years that long had been conjectured.

Indeed, life may have arisen more than once, some speculate, somehow
making the transition from inanimate mineral to living organism under
conditions that almost certainly would be lethal to the life dominating
Earth today.

Researchers are exploring ways these pre-biotic compounds--as the
nonliving precursors of the first molecular life are called--may have
developed from more basic chemicals.

"What is the nature of the first genetic material and how do you make the
building blocks?" asked Miller of UC San Diego. He has spent almost 45
years trying to duplicate the original chemical formula for creation.

As much as anyone, it was Miller who took the question of life's origin
beyond speculative metaphysics or theology and into experimental
laboratory chemistry.

While a graduate student in 1953, he conducted a now-legendary
experiment in which he filled a beaker with his best guess of the Earth's
early atmosphere, jolted it with electricity and produced a rain of amino
acids critical to all living things.

Today, as one of the collaborators in the NASA project, he still is trying
to answer the question that launched his career.

"You have the pre-biotic soup. There is still this question of what is in
the soup," he said.

Using gases that may have dominated the planet's early atmosphere, Miller
and his collaborators so far have managed to create 13 of the 20 amino
acids utilized for organic life in his test-tube Earth.

But researchers must work blindly, for time has erased any clues to the
nether world in which life first arose more than 4 billion years ago. Not
everyone thinks he has the right idea about the early atmosphere's
composition.

"Since we have no record of Earth's earliest history, we have to
speculate,"
Arrhenius said. "But it has to be based on what we know of geophysics and
geochemistry. Researchers in this area--chemists in particular--commit the
sin of ignoring the ground rules."

Researchers are certain the early Earth and its atmosphere were radically
different from what exists today.

There probably was no oxygen in the atmosphere, so it would have been
poisonous to life as it is known now. Scientists also agree that the sun
was
25% dimmer, while its ultraviolet radiation may have been up to 32 times
more intense. Those differences are important because even a slight
decrease in the sun's brightness could drop temperatures to 40 degrees
below zero.

With so little else certain about early Earth, there is almost no limit on
the scientific imagination. So, there is no shortage of theories about the
original chemistry of life. None can be proven--or disproven--and each
contains at least one seemingly fatal flaw.

One leading theory notes the consequences of a weaker sun shining on the
primordial planet.

Bada and other scientists speculate that on the early Earth all but the
ocean depths must have been frozen solid. Under that scenario, life may
have
developed around hot volcanic vents on the ocean floor. Crucial organic
compounds could have been delivered by comets and meteors smashing
through the icy crust.

Some researchers, however, question whether fragile organic chemicals
could survive the fiery shock of a comet impact. Bada has suggested that
they may have been protected by traveling inside the armor of special
carbon molecules.

Gases spewing from the comet as it sped toward Earth also could have
lingered at high altitudes. In research made public last month,
Christopher
P. McKay and William J. Borucki at NASA's Ames Research Center
suggest that shock waves generated by comet impact could turn trace gases
into complex organic compounds in the atmosphere, much as lightning will.

In any case, the idea of comet chemicals brewing under an icecap has
captivated scientists who think Europa may be home to life.

Intrigued by new images released by the Jet Propulsion Laboratory last
month, some researchers speculate that organic matter--and, perhaps,
extraterrestrial life--may be developing in an ocean concealed by the tiny
moon's miles-thick sheath of ice, kept warm by the heat of its core.

Some biological evidence on Earth lends credence to this idea.

During undersea volcanic eruptions, researchers often detect microbes that
developed under the extreme conditions prevailing inside the Earth's rocky
crust. Some of these microbes grow in water as hot as 235.4 degrees.
Indeed, the earliest known bacteria seem to have evolved in conditions of
extreme heat.

In April, two German researchers offered new experimental evidence for
the idea that life began around the red-hot lava of a volcano. By
re-creating the chemistry of deep sea vents in the laboratory, they
synthesized some
key chemical steps necessary for the creation of biological molecules.

"The conditions of our reaction may be taken as a model for understanding
the habitats of primitive forms of life on Earth or Mars," concluded
Claudia
Huber and Gunter Wachtershauser.

But critics say the water circulating through those volcanic vents on
Earth,
heated by magma to more than 600 degrees, is so hot it would have
destroyed any simple organic compounds.

Others researchers scoff at the thought that life developed in a deep
freeze. They contend that the early Earth may have been kept warm by an
atmospheric greenhouse effect caused by high levels of carbon dioxide.

But that idea also has problems.

For the necessary greenhouse effect, the early atmosphere would have
required a level of carbon dioxide 100 to 1,000 times higher than today--
high enough to quash most organic chemical reactions, researchers say.

In yet a third theory, some researchers argue that the oceans could have
been kept liquid--a prerequisite for life--by the internal heat of Earth's
newly formed core. Others suggest that in the period when life is believed
to have begun, the oceans may have been periodically vaporized in plumes
of steam by the impact of comets and huge meteors.

Even the presence of liquid water--so crucial to the maintenance of life
today-could have hindered its development on primordial Earth.
Experiments show that water can interfere with the growth of the kind of
complex molecules needed to develop life.

So many uncertainties are enough to frustrate the most dedicated optimist.

Forty-four years ago, when Miller first performed his ground-breaking
"genesis" experiment, the creation of life "looked so simple and so easy,"
he recalled.

"It turned out not to be easy," he said.

Copyright Los Angeles Times

Oryginal: http://www.latimes.com/HOME/NEWS/SCIENCE/REPORTS/CREATION/story.htm