Can
Science Produce Life?
By
RUTHERFORD PLATT
For years scientists have carried on a wave of unprecedented laboratory
experiences to test their theories of how life on Earth began. The results have been amazing. Retracing the probable steps by which the
raw, lifeless elements of space became organic matter, they now have produced
primitive cell-like structures that have many of the properties of living
cells. Here is the dramatic story:
When Planet Earth was born it slowly cooled to form
a hardened crust of black volcanic rock.
In time, masses of silicon mixed with mineral elements were squeezed to
the surface by the pressures of internal fires, and crystallized as big islands
of granite, which formed the foundations of continents. The whole crust heaved and bulked,
cloudbursts drenched the rocks, and sterile water collected in wide depressions
to form the earth’s first seas.
Countless volcanoes and fissures continuously gushed methane, steam,
ammonia and perhaps carbon dioxide, to give the earth its first
atmosphere. That ‘air’ contained the
four chief elements of life—carbon, oxygen, hydrogen and nitrogen. But they were in the form of gases deadly to
present-day life. Moreover, the
atmosphere was flooded with ultraviolet radiation and stabbed by incessant
lightning.
How, in this elemental turmoil, did life on earth
begin? Many have tried to supply the
answer. Among the first was Anaxagoras
of Greece, who in the fifth century B.C. declared that life comes down to earth
in raindrops, in the form of spermata [little seeds]. Came the 20th century, and the origin of life was
still a mystery.
Then in 1924 the Russian scientist A.I.Oparin stated
that life might have arisen out of inanimate matter in a prolonged process of
‘preorganic evolution.’ He showed how,
in theory, atoms of carbon, oxygen, hydrogen and nitrogen could have formed
molecules basic to life, even under the raw, inhospitable conditions of the
primordial earth—and how self-reproducing clusters of these molecules might
have adhered together and then evolved toward more complex forms.
Three years later the English biochemist
J.B.S.Haldane wrote that although such substances would be destroyed by
microorganism, “before the origin of life they must have accumulated till the
primitive oceans reached the consistency of hot, dilute soup.” And when the ultraviolet light radiated the
surface of this soup, inorganic compounds would have been converted into
organic molecules—molecules containing carbon.
At once time scientists believed that only living things could produce
such organic molecules.
By the 1050s the scene was shifting from the
theorist’s armchair to the laboratory, where scientists were striving to
demonstrate that the molecular constituents of life could have emerged under
primordial condition.
Using the cyclotron at Berkeley to create
high-energy particles to represent cosmic rays, Dr. Melvin Calvin of the
University of California bombarded a mixture of carbon dioxide and water vapor;
ingredients he thought likely to have been present in the earth’s ancient
atmosphere. Some organic compounds were
formed.
Dr. Harold C. Urey, atomic scientist then at the
University of Chicago, reasoned that methane, ammonia and hydrogen were
probable constituents of the original atmosphere. What would happen, he wondered, if these raw lifeless substances
were placed in a flask and then stabbed repeatedly by electric flashes to
represent lightning? In 1953 his
student Stanley L. Miller performed this now classic experiment. To their delight, they found that amino
acids had been formed.
Amino acids are the building blocks of protein and
hence of all life. They are also
believed to have been involved in the first stage of the evolution toward
life. The theory is this:
The colossal retort of the primordial earth must
have yielded myriads of molecules as ephemeral as bubbles. But, because of their peculiar molecular
structure, the molecules of amino acids are especially stable. The four elements of life—carbon, oxygen,
hydrogen and nitrogen—are assembled in every amino-acid molecule into two
opposing groups so well-matched in their electrical charges that they are
stabilized like wrestlers locked in equal combat. Thus the tenacious amino acids could have survived in the chaos
to become an early link between no-life and life.
In experiments that followed, a surprising fact
turned up. The basic molecules of life
could also have been produced by many other forces in those fierce, elemental
times, including X rays, cosmic rays, ultraviolet light and volcanic heat.
After the creation of amino acids, two even larger
problems remained. Giant protein
molecules, discovered everywhere in living things, are made of long chains of
amino acids. How did the amino acids
get hooked up into these long chains?
And then how did these twisted protein giants turn into living cell?
Giant proteins are fantastically elegant
structures—“the noblest piece of architecture produced by nature” in the
opinion of biologists. One molecule of
the vital protein of blood, hemoglobin, for example, has 8954 atoms fitted together
in a dazzling pattern. The problem is
that all the complicated proteins in life around us—living cells create those,
which make flesh, blood, bone, hair, eggs, milk, seeds, and feathers—. Those living cells in turn are made of
protein. How could protein be created
in the first place, when there were no living cells?
This question is puzzling many scientists around the
world. No one has yet developed a
foolproof theory that explains which steps came first of what triggered
them. One line of reasoning, first put
forward by Dr. George Wald of Harvard, is that there may be conditions
occurring in nature in which amino acids might themselves furnish the
answer. And so they did—quickly and
beautifully—when the stage was set for them by Dr.Sidney W. Fox, then of the
Institute of Molecular Evolution in Miami, Florida. The “miracle” occurred when amino acids were permitted to dry
out. The thinking was that solutions of
amino acids, billions of years ago, had puddled in warm, dry spots. What would happen to such solutions today if
the water was allowed to evaporate? The
scientists who watched this experiment saw a marvelous event.
As the spot on the warm test tube dried, its amino
acids formed long, submicroscopic thread-like structures. These chains some with hundreds of little
molecules jointed end to end, were named proteinoids. The sum of their electric energies endowed them with power to
bend and fold!
There are 20 kinds of amino acids common to the
proteins of life, and the precise order in which these are lined up in the
chains spells what their protein creates—flesh of bone, hair of feather. The scientists have been able to manufacture
all these amino acids under presumed primordial conditions. Dr. Kaoru Harada was able to synthesize 14
in a single experiment.
So the answer to one question is found. Amino acids by themselves can produce
primitive protein-like material under certain conditions—no need for a cell to
help them.
Still, the final question remains. How could these proteins from a living cell,
with its millions of atoms and molecules carefully arranged in a precise
pattern?
The primitive proteins came long before living cells
appeared. The precisely ordered
proteins of present-day plants and animals would have acquired their amino-acid
arrangement in the course of many millions of years of evolution. Dr. Calvin estimated that molecular life
must have evolved for two billion years before the first living cells appeared.
Duplicating this great leap, making a whole living
cell in the laboratory, may take a while.
But it now appears that we’ve begun.
The most striking experiment, which has produced crude cell-like spheres
that maintain their identity and are capable of dividing themselves, is truly
fantastic and has taken us a giant step along the pathway toward understanding
the origin of life.
Again, Dr. Fox did the experiment. To reconfirm his laboratory findings, he
climbed up the broad slope of a cinder cone in Hawaii, looking for spots where
conditions might have permitted primitive proteins to form in the pre-life
world. He was surprised to discover
that large areas of the cone were oven-hot just beneath the surface. Might not this warm primitive earth have
been the womb of the molecules of life—where they could bake and boil, before
being washed through the loose lava by a cloudburst and so into the sea? What would this have done to the elemental
amino acids?
Dr. Fox took hunks of lava back to the laboratory
and placed on them amino acids coined from methane, ammonia and water. With everything sterilized to avoid
contamination, he baked this concoction for a few hours in a glass oven at
338-degree F., the temperature he found four inches under the surface of the
cinder cone. When the materials cooled,
a brown, sticky residue was left clinging to the lava. He then deluged the lava with sterile water,
and a brown soupy liquid resulted.
This unpromising stuff turned out to be very
exciting. As seen through an ordinary
optical microscope a wonderful galaxy of spheres swarmed across the field of
vision. The amino acids had first
united to make proteinoids—and then these had combined to form little
spheres! Dr.Fox named these fascinating
strangers ‘microspheres’.n they looked
like, in many ways behaved like, and were the same size as certain simple
bacteria, and they clung together in chains as do the one-celled blue green
algae. Bacteria and blue-green algae
are two of the most elementary forms of life that exist on earth.
Although these spheres are not true cells—they have
no DNA genes and they are simpler than any contemporary life—they do possess
many cellular properties. They have
stability: they keep their shapes indefinitely. They stain in the same way as the present-day protein in cells,
an important chemical test. But the
real significance of these micro spheres is that scientists did not synthesize
them piece; they simply set up the right conditions—and micro spheres produced
themselves.
In the meantime, scientists working independently in
other laboratories are making DNA and other essential constituents of the
living cell could have formed. It
becomes hard to avoid the premise that life is inherent in matter, and that
life will exist on other planets whenever the conditions are right.
