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 ?, 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?

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