Formation of Organic Molecules,
the Haldane-Oparin Hypothesis
The early chemical steps toward life have a good theoretical
basis. The basis is found in a 1920’s
hypothesis credited to a Russian biochemist, Alexander Oparin, and an English
biologist, J. B. S. Haldane. Each
hypothesized the first formed atmosphere lacked oxygen, but contained ammonia,
and had reducing properties. The
chemicals of the atmosphere interacted in the presence of ultra-violet light,
lightening, and volcanic heat to produce the chemical precursors of living
systems. Biologists think the precursors
accumulated in the water and somehow assembled into primitive living
systems. Such steps were necessary
because free oxygen is produced by photosynthesis and would not have existed in
abundance prior to photosynthetic organisms.
The ammonia was formed as it can be today from the effect of
lightening upon atmospheric nitrogen and water vapor. Carbon dioxide was abundant in the early
atmosphere.
An experiment in 1953 by Stanley Miller and Harold Urey in
Chicago . . . . . .used sparks in the atmospheric portions of the system to
simulate lightening. They cooled a
portion to condense water along with products in solution that were present or
produced. Analysis of the condensate
showed some amino acids and other organic compounds, most of which are
components of living systems.
Concentration of
Organic Molecules
The most important mechanism may have been concentration by evaporation
of water. Low tide could have made it a
daily event in intertidal areas. But
higher splash zones may have had longer periods of isolating pockets of water
for greater concentration.
A second mechanism is by coacervate production. The coacervates are small globules of organic
material that accumulate other organic molecules because their solubility in
each other is greater than their solubility in water. This . . . . . .could have been the route of
biological membrane formation. Membranes
. . . form naturally in systems where an abundance of the proper lipid
molecules are present. The water insoluble
ends are semi-dissolved in each other and repel the water soluble ends so a
double layered membrane forms automatically.
The third mechanism, adherence to particulate items may have been
especially prominent in pockets of water along the shore. It might be thought of as the “bathtub ring”
origin of life. It is perhaps the least
certain of mechanisms, but seems a possible explanation for aiding the origin
of some of the biochemical processes where minerals are important
components.
[The preceding is adapted
from pp. 74 and 75 of my 2009 Evolution
Insights unpublished manuscript.]
Alternative Views of
Organic Molecule Formation
An alternative view of the origin of life was proposed by a
marine biologist, Corliss, who, noting the abundance of life at deep sea vent locations where the animals surround volcanic heat and emissions produced chimneys,
suggested such sites were where it all started.
An earlier experimental observation by a scientist at a newly formed
island near Iceland showed that lava and seawater interact to produce a few
amino acids and small organic molecules.
In the early history of the earth lava/seawater interactions were
presumably more widespread and included many more shallow water locations. Such locations undoubtedly contributed to the
organic content of the original oceans but are unlikely to have been the
location where animals originated for two reasons. One, they come and go with change in lava
production and are limited in geographic extent to mostly where crustal plates meet. Two, the fossil record indicates
older forms of life seem to have originated in shallow coastal areas and
progressively over time show representatives in deeper waters.
Few accept biblical accounts of creation of life details. Certainly, God could have created the world
and its inhabitants, fossils and all, in a short time, but doing it in the billions
of years and with the details supporting the amazing story of evolution seems
like an even grander way and leaves people with the kind option of not
demanding immediate belief in an infinite deity that is all loving, kind, and
merciful.
Evolutionary
Consequences of the Haldane/Oparin Hypothesis
1. The first compounds formed, including such amino
acids as glycine and adenine, became important building blocks for living
systems. Adenosine triphosphate, the
energy currency of the cell, and the unique structure of DNA with adenine as the basis for one of its
four nucleotides of the genetic code, were important consequences.
2.
Functional values of early steps were retained
as basic, but slightly modified, characteristics seen in descendant organisms. The gradual changes leave helpful clues for tracing the evolutionary history of animals as well as plants.
3.
Photosynthesis, upon which we are so dependent
today, makes shallow seas and coastal regions the most likely place of life's origin.
4.
DNA’s early origin before the oxygen laden
atmosphere developed meant the development of the nuclear membrane probably
developed after photosynthetic bacteria.
The nuclear membrane enables DNA to operate in the part of the cell where
it experiences the cell's lowest oxygen content area most like it experienced in its
early origin.
5.
Billions of stars have planets where now or in
the past similar conditions led to production of the same basic building
blocks. Such beyond earth production makes it quite possible that
fragments of extraterrestrial bodies containing such organic compounds may have impacted earth without proving
life was present on the source planet. Planets in other galaxies, as well as in the Milky Way, have undoubtedly had similar periods with similar conditions to earth with somewhat similar evolutionary histories of life.
Joseph G. Engemann, Emeritus Professor of Biology, Western Michigan University, Kalamazoo December 15, 2016
