"Thomas A. Easton - Life is in the Stars" - читать интересную книгу автора (Easton Thomas A)

solution together with many salts. The energy which drives the reactions turning these chemicals
into more complex ones, eventually leading to proteins and living cells, comes from lightning,
from the sun, as light, heat, and ultraviolet, and from the Earth itself, as heat and radiation.

Accordingly, the atmosphere which enveloped the newly-formed Earth five billion years ago would have
been composed of water vapor, carbon monoxide, carbon dioxide, methane, ammonia, hydrogen sulfide,
sulfur dioxide, and a few of the rest of the gases derivable from the lighter elements. There would have
been no oxygen at all, of course, for there would have been no plants to make it, and the air of that
long-gone era would have been a noxious, toxic brew few organisms alive on Earth today could survive.
Still, it was the brew which gave Earth life.

The Earth itself, as soon as it had cooled enough to have a solid crust and liquid seas, would have been
very different from what it is today. There would, of course, have been no sedimentary rocks, no coal, no
oil, and no fossils. The hot rains might have been acid from the volcanic fumes that filled the air. The
rocks would not have been the familiar red and brown we know today; they had not yet been exposed to
oxygen, and the unoxidized iron in them would have left them colored black and green. The ultraviolet
light from the sun would not have been screened by ozone, for that must come from oxygen. But the seas
(comforting thought!) might have been no less salty than they are now; all the salt leached by rain and
groundwater from Earth’s rocks since then may be well represented by the salt beds left behind by
dried-up seas.

Some of the energy that entered this system can be attributed to background radiation, about three times
the present value, to meteoritic shock waves, and to cosmic rays. But most of the energy would have
come from the electrical discharges, the lightning, that must have thundered a stormy accompaniment to
the volcanoes and earthquakes of a calming planet, from the volcanic heat and heat from the Earth’s
core, and from the heat and ultraviolet of the sun. These are the energies that in time transformed the
chemicals of the primordial atmosphere into the life we know. And other worlds, of other stars, must
share them, as they must share the interstellar starting point. If less energy is available to them, as when
they circle farther from their stars, there is still no reason to think that life cannot arise on them; it must
only take longer to do so, for chemical reactions are stopped only by a complete lack of energy.

How did life begin? The philosophers and the biologists phrased the question, but they were not
equipped to answer it until 1913, when W. Loeb exposed mixtures of carbon monoxide, carbon dioxide,
ammonia, and water to electrical discharges and obtained glycine, one of the amino acids crucial to life as
we know it today. He did not perform his experiments with any intention of imitating the conditions of the
primordial Earth, but his results did indicate how the first complex organic compounds could have been
formed.

Not until 1953, however, was a truly close approximation to the primordial atmosphere tested. Then
Stanley L. Miller, working with Harold Urey at the University of Chicago, exposed mixtures of methane,
ammonia, water, and hydrogen to electrical discharges and obtained many organic compounds, including
several amino acids.

Since that time, numerous experiments, using many combinations of the chemicals thought to have
occurred in the non-oxidizing primordial atmosphere and all of the possible energy sources, have shown
that primordial atmosphere to be capable of giving rise to most of the chemicals we now find in living
things. The chemists have even found that some of the reactions that produce this wealth of pre-biotic
material seem to be most fruitful when the energy source is heat and the reactions occur on or about hot
dry sand or lava. When the heat is applied to solutions of the gases typical of the primordial atmosphere
and various salts in water, the same reactions may occur at much lower temperatures, even well below