Term Paper: Beginnings of Life on Early Earth

Pages: 5 (1585 words)  ·  Bibliography Sources: 1+  ·  Level: College Senior  ·  Topic: Chemistry  ·  Buy This Paper

¶ … Life on Early Earth

Questions related to the origins of life on Earth have always been a cause for scientific investigation and suppositions. If we refer to the naturalistic approach, than the evolutionary process is a justified explanation of changes and transformations that have occurred. This is a theory that we can successfully apply to the appearance of life on Earth and to the chemical processes that have made it possible.

It is interesting to note that such demonstrations related to the origins of life on Earth have the downfall of being strictly scientific, in the sense that new observers were present during those times to certify whether they are true or not. Indeed, everything is related to chemical formulas, to suppositions and hypothesis.

The original life forms are deemed to have been formed from a large number of highly complex molecules, a number ranging larger than 1,000, but without being clearly identified. Indeed, Van Rensselaer Potter states that "it is possible to hazard a guess that the number is not less than 1,000, but whether it is 3,000 or 10,000 or greater is anyone's guess." Further more, these primitive life forms had, in their composition, complex proteins, amino acids, DNA and RNA molecules and other particular cellular components, which makes the chemical evolution explanation not necessarily highly improbable, but more difficult to sustain.

We may assume that the primordial atmosphere on Earth was formed of ammonia and nitrogen, carbon dioxide, methane, hydrogen and water. As we can notice, the primordial Earth atmosphere has no oxygen, because, otherwise thermodynamically oxygen would have instantly transformed all substances into oxidized products, thus leaving no source for chemical evolutionary processes.

Following several definitions, chemical evolution can be characterized as "the view that life originated through purely chemical transformations of nonliving matter. Starting from primordial simplicity, such chemical transformations are supposed eventually to have brought about a living cell."

Classifying organic matter in such substances as sugar, amino acids or proteins, we should briefly refer to Miller's experiment that created these substances in the laboratory from substances existing in primordial conditions and that practically explains the chemical evolution hypothesis theoretically defined here above. His experiment led to the formation of glycine and alanine, two of the simplest amino acids, glutamic and aspartic acids, all of which contribute to the formation of protein. Following his research, several scientists were keen to note that the primordial conditions on Earth were suitable for a chemical evolutionary process that would have, in time, led to the creation of simple life forms on Earth.

There are however several problems that arise from Miller's success and which have led to several other theories, most notably that prebiotic material was rather brought to Earth from elsewhere. First of all, Miller's experiment used several conditions a priori, conditions which we are not sure would have existed in primordial atmosphere. For example, his experiment isolated some of the substances produced from the source of energy that was used. On Earth, this would not have necessarily happened and it is most likely that, following the process described by Miller, these substances would have been extinguished before being able to give birth to new chemical reactions, in compliance with the chemical evolution hypothesis.

Second of all, we may assume that these organic substances formed in the atmosphere would have been able to reach the ocean and would have properly developed here. However, this is where timescale non-concordance poses additional problems. Indeed, in order to survive, these substances would have needed a temperature of 0 degrees or lower. However, these processes are placed somewhere around four billion years ago and it seems impossible to assume that the Earth surface would have been cooled from its molten lava state in such a brief period of time, two billion years from its creation. Further more, scientists have estimated a period of at least four and a half billion years before the Earth reached its present temperature state. As such, on one side we are concluding that the ocean had a temperature of around 0 degrees four billion years ago, so that the organic substances would have been able to survive, on the other side, we know that the Earth reached the temperature we have nowadays only some one and a half billion years ago.

Following this train of thought, it seems clear that we should also consider some external stimulus that may have been at the origin of life on Earth and this stimulus may well be represented by organic material brought to Earth from other planets by comets or extraterrestrial bodies.

As I have previously objected to the survival of organic matter produced on Earth, it seems logical to ask ourselves whether such matter would have survived upon the impact between the comet and Earth. For this, I will be following the conclusions of an experiment presented on the BBC News website.

The experiment is rather simple and implies shooting a "can-sized bullet on to a coin-sized metal target containing a droplet of water mixed with amino acids, the building blocks of proteins." The results showed that not only had the amino acids survived, but some of them had created peptides, which are proteins and a form of organic material.

The additional problem implied by the comet theory is that, in order to survive and evolve, the organic matter would have required water (as I have previously discussed here above). The experiment showed that at very low angle collisions, the icy comet, hitting Earth at 25 km per second, would have had every chance of transforming into liquid. Its initial icy form would have been an argument for the appropriate temperature necessary. Of course, we are now turning to probabilistic suppositions and chance theory: what were the chances that such a comet has indeed hit the Earth and gave way to life here? We should assume the fact that the period we are referring to was a period of intensive comet bombardment of terrestrial surface and that the chances of comets hitting the ground on a low angle would have been quite elevated. Further more, calculations showed that it was possible and highly probable that a few percent of the total number of comets hitting Earth during that period would have made it at the right angle.

In order to further argument the comet impact theory, we should have a brief discussion around what such comets may have brought to Earth and what chemical components the comet material was actually formed off.

A comet is made up off ice and cosmic dust. We are interested in both here. Indeed, the ice part is formed both of frozen water and frozen gases from the Universe, including nitrogen or hydrogen. Cosmic dust has different components, ranging from gases (carbon, nitrogen, oxygen) and inorganic molecules, such as methane or ammonia, to organic molecules such as "hydrocarbons, polyaromatic hydrocarbons, the amino acid glycine, vinegar and the sugar glycoaldehyde" and even to primitive life forms, such as bacteria.

As such, it is more than plausible that comets carrying organic or inorganic molecules and primitive bacterial forms would have hit our planet some four billion years ago, when life is believed to have begun on Earth. Further more, as we have seen from the presentation here above, this scenario was probably more likely to have happened, since it had all the required elements: water from the impact at a certain angle (as we have seen, the odds for this to have happened were quite high), organic matter present in cosmic and interplanetary stardust and the right temperature in the poll thus formed.

If we follow the comet theory, we may first of all underline the fact that this theory of life origins is completely independent from conditions on Earth at that… [END OF PREVIEW]

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