FREE ESSAY ON THE ORIGIN OF LIFE

THE ORIGIN OF LIFE

The origin of Life
There are many theories where life came from, but none of them is proven to be the right
one. The obvious theory that life originated on earth is not accepted by everyone. One
reason of disbelief in this theory that life originated on earth is a lack of time. It
was an early belief that life originated through a slow and long process (many scientists
do not share this belief though), probably too short and too long for the time life had
on our planet. Life must have been formed within a period of approximately 200 million
years. If we represent the whole Christian era - two thousand years - by one inch, the
time available for the emergence of life could measure as much as 1.5 miles. Another
theory called panspermia claims that life was created somewhere else, not on earth, and
traveled to our planet via meteorites or comets. Another version of panspermia claimed by
Francis Crick and Leslie Orgel is that life was brought to earth by a spaceship sent by a
more intellectual species. This theory is called directed panspermia. The last theory
might be the least likely one, since there is no actual evidence for spaceships or
species from other planets. The panspermia theory can not be disproved and it might be
possible that life came to earth via a comet. Bodies like comets contain organic
molecules which are similar to the molecules of living organisms, but most scientists say
that reactions creating these molecules take place out there. We can not find an answer
for this question since neither theory can totally be proven. Supporters of the
panspermia theory say that there was not enough time for life to originate. Supporters of
the theory that life originated on earth can not prove that life did not come from outer
space. The Christian theory that life was created by God is abstract and will not be
discussed further in this paper. Personally I believe in the theory that life was born on
earth. 
Six elements are needed to create life. Almost every organic matter can be summarized
symbolically in these six different elements: carbon (C), hydrogen (H), nitrogen (N),
oxygen (O), phosphorus (P), and sulfur (S). One also says that life can be explained by
the formula CHNOPS. These are the main characters in the creation of life chemically.
Knowing that these six elements are needed to create life we have to find out in what
condition these elements were. 
It is still not known what the composition of the primitive atmosphere was. It was
believed that the atmosphere consisted of hydrogen (H2), methane (CH4), ammonia (NH3),
and water vapor (H2O). But this is doubted today. Scientists say that carbon probably was
not present in the combination with hydrogen (methane). It probably was present in the
combination with oxygen, mostly with carbon dioxide, or CO2. In the early years of the
earth, about 4 billion years ago, there was no oxygen in the atmosphere of the world.
There needs to be life in order to have free oxygen.
What was the temperature on earth in these days? It is practically impossible to find the
answer to this question, but it is an important issue to know since temperature limits
the life span of biomolecules, such as proteins, nucleic acids, and the blocks they were
contained in. Thinking of this fact chemists assume that the temperature of the
environment might have been very cold, possibly under the freezing point. Geochemists,
though, do not think this way. They believe that temperature might have been close to the
boiling point of water, but they also believe that there must have been a high
atmospheric pressure, which kept the oceans from boiling. 
What was the sun like? Four billion years ago the sun was cooler than today. It sent out
probably 25% less energy to the Earth than today. But this was probably offset by the
greenhouse effect of atmospheric carbon dioxide. 
There definitely was a lot of water in the beginning of life. Water is the vital element
of any living organism. The atmosphere above the water was heavy with carbon dioxide,
nitrogen, hydrogen sulfide, and water vapor, but most likely poor in hydrogen. 
Stanley L. Miller decided to find out how lightning might have affected an atmosphere,
which he believed was a hydrogen-rich mixture of molecular hydrogen, methane, ammonia,
and water vapor. Miller simulated thunderstorms by producing repeated electric discharges
inside a sealed glass enclosure containing a gaseous mixture of methane, ammonia, and
hydrogen, through which water was continually recycled by evaporation and condensation,
as would have happened over a primeval ocean. Miller actually found several amino acids
and other organic molecules when he analyzed the water after a few days. The result of
this experiment is deeply questioned. If one changes the conditions of the atmosphere in
this glass slightly one will not find any organic molecules in this glass. 
The Murchison meteorite, falling in Murchison in 1969, contained simple amino acids.
These amino acids were similar to those amino acids which Miller found in his experiment.
This shows us that organic compounds can survive the crash through the atmosphere. It is
also evidence that simple forms of organic compounds can be created under primitive
conditions, not only on Earth, but also in space, and on comets and meteorites.
The seeds of life definitely are in a form of various combinations of carbon, nitrogen,
hydrogen, oxygen, and sulfur. Influenced by electric discharges, radiation, and other
sources of energy, the atoms were reshuffled to produce amino acids and other basic
biological building blocks. 
Assuming that amino acids were formed somehow what happened next? It is a long way from
an amino acid to a single cell. One might believe that the next step was the formation of
proteins, since proteins consist of amino acids. But this is not true. According to
majority opinion, proteins must have been preceded by ribonucleic acid (RNA). The main
reason for believing this is that in today's world RNA molecules provide the catalytic
machinery and the information for the formation from amino acids into proteins. One could
argue, though, that no protein could arise without the help of protein enzymes. That
means protein makes RNA, which then makes protein again, which makes RNA, and so on. This
is comparable to the famous chicken or egg problem. 
Crick's Central Dogma stated that information flows only from nucleic acids to proteins,
never the other direction. This means RNA came before proteins. Gilbert defines that RNA
world as a stage in the early development of life in which 'RNA molecules and cofactors
[were] a sufficient set of enzymes to carry out all the chemical reactions necessary for
the first cellular structures. 
What is RNA? RNA molecules are long chainlike assemblages made of a large number - up to
many thousands - of units called nucleotides. Each nucleotide consists of three parts:
phosphate, ribose, which is a 5-carbon sugar, and a base, of which there are three
different kinds - adenine, guanine, cytosine, and uracil. It is not known how RNA got to
be on earth. The first RNA molecules were probably random association of nucleotides. As
we know, RNA translates information from the DNA and that is how proteins are made. 
With this scenario one or more RNA variants interacted with amino acids in such a way
that the amino acid became linked to the ribose end of the RNA molecule. This is how the
primordial gene started the long evolutionary journey that eventually gave rise to
transfer RNAs. This is how it is today. They join with amino acids in what happens to be
the first step of protein synthesis. 
What happened next? All the RNA strings probably formed hundreds of minigenes. They had
to do base pairing, replication, splicing, and translation. The more complex they became
the more work needed to be done. There was only one way out. They had to divide the work.
Replication had to be separated from translation. DNA emerged. 
As a result there were many minigenes which were modified and combined in different ways
into larger assemblages that were then screened by natural selection. To have a fully
operational genetic system to develop, emerging life needed to become made into a
population of multiplying by division, so that protocells, not just molecules, were
subjected to natural selection. 
Out of this the first cell emerged. We can assume that all living organisms come from
this cell, a common ancestor to all living organisms. It is overwhelming to hear this and
we have to believe it as long as the opposite has been proven. The first cell must have
been an organism of prokaryotic type (microorganism of bacterial type). Bacteria are
built to grow and multiply as fast as materially possible that is why it was so
successful to grow and evolve to complex organisms. Out of the prokaryotic cell an
eukaryote cell (living organisms - compromising protists, plants, fungi, and animals,
including human) must have emerged. It is uncertain how this happened. It is believed
that a prokaryote cell detached from the archaebacterial branch. 
Many things have not been discovered about the origin of life. There are many theories
and it will take a long time until everything will be determined. To this point none of
the theories could be strongly proven. The most believed theory might be that life really
originated chemically on earth. If one believes that life was brought to earth, either by
a meteoroid or by aliens, there still is the question how life originated. Perhaps some
aliens really brought us to earth, who knows?