Undersea Vents Reveal About Life’s Origins

Formation of Solar System

Describe about the Undersea Vents Reveal about Lifes Origins?

1. The solar nebula hypothesis is the most proposed model that is related to the formation of the solar system including the formation of the Earth. According to this model, a large cloud of gas and interstellar dust which is rotation is the creator of the solar system. The gases include mostly hydrogen and helium. The acceleration of the cloud resulted in the formation of gravity, angular momentum and inertia which in turn resulted in the flattening of the cloud forming a protoplanetary disk which lied perpendicular to the axis of its rotation (Liffman, 2009). As compared to the outer side of the nebula, the inner core had a low angular momentum that resulted in the contraction of the centre and the heating resulted in the nuclear fusion of the hydrogen and helium. As the contraction increased, it rested in the ignition of T Tauri star that in turn evolved into the Sun.

On the other hand, the gravitational force on the outer part of the nebula resulted in the condensation of matters around the dust particles and the perturbations. The clumping together of the comparatively larger fragments of the debris and dust resulted in the formation of planets in a process called runaway acceleration (Matson , 2010). The Earth was also formed along with the other planets around 4.54 billion years ago and the completion of the formation took another 10- 20 million years (Newman and William, 2007).

The Earth formed in this manner, called the proto-Earth grew in size as a result of the acceleration. The model that is related to the formation of the only satellite of the Earth i.e. the moon is the giant impact hypothesis. According to this hypothesis, when a body with a size of the Mars, hitted the Earth, the collision resulted in the formation of the moon.

After the formation, the surface of the Earth cooled down gradually. At that time the atmosphere was mostly composed of carbon dioxide, molecular hydrogen, water, molecular nitrogen, carbon monoxide, hydrogen chloride and very little amount of reactive molecular oxygen. As the cooling process continued, it resulted in the formation of a rocky crust, between the 0.2 – 0.4 billion years ago, that was stable.

The origin of life reported to begin about 3.8 billion years ago. The proof of the origin of life is associated with the discovery of zircons from the Western Australia rocks that are dated radioactively to be 4.25 billion years old. The studies carried out by Nemchin et al., (2008) revealed that the light- carbon isotope ratio, which was unusually high in micrometer sized graphite and diamond inclusions that were also considered as zircons, were the indication of biological origin. These findings suggested that there were carbon based life within the first 300 million years of the formation of the Earth.

Again according to Mccollom and Seeward (2006), the high concentration of carbon- 12 isotope compared to carbon -13 isotopes in the zircons indicated that there were organic materials present at that period of time. Whereas some studies indicated that the C- 12 abundance could be brought about by some chemical reactions of non biological origin, others showed that the abundance was due to the presence of organic compounds that were simple in nature and were responsible for producing an environment that was later suitable for the origin of life on the Earth.

Formation of Earth

Again recent studies by Bradley A. (2009) suggested that during the first billion years of the existence of the Earth, the carbon based and self replicating microbial life was well developed. Studies also indicated that some microbial life flourished within the warm, deep and boiling hot springs, the cracks in the crust of the seafloor without any oxygen or light.

Again, the Earth at that time had very little amount of molecular oxygen and a very large amount of molecular hydrogen. In the absence of oxygen, the concentration of hydrogen increased considerably in the ocean and the atmosphere, which resulted in the growth of methanogens. So, in the harsh environment of the Earth, the microbial life flourished that in turn paved the way for the development of more complex life form in the Earth. Studies are still going on to find more and more evidences regarding the origin of life on the Earth.

2: Nearly 500 planets were discovered that are known to orbit around other stars in the universe and there are about 100 billion galaxies and the number of stars in our galaxy is about 200 billion. It has also been discovered that the number of planes with the same size as that of the Earth in our galaxy are 17 billion. According to the data provided by the Kepler mission of NASA, it has been found that every sixth star has a planet that has similar size to the Earth. If we consider this equation, we can easily say that there is a strong possibility of life in planets other than the Earth.

Again we have found that life is possible without the presence of oxygen (anaerobic microbes) even in very harsh condition. So, there may be life in planets that are yet to be discovered. The Universe is a vast thing, full exploration of which is impossible, so, we might not encounter another planet with the existence of life, but we cannot deny that life is not possible outside the Earth. According to Loeb (2014), about 13.8 billion years ago, after the Big Bang, life may have begun, when the age of the Universe was only 10-17 billion years during a habitable epoch. As per the studies carried out on a computer based model by Moskowitz and Clara (2012), the complex molecules that are organic in nature and required for the formation of life, may be originated before the origin of the Earth i.e. in the protoplanetary disk which was consisted of dust particles. So, according to them, life can also originate in other planets around a star in the same process. According to other studies, the places other than the Earth that have the potential of origin of life include Mars, Venus (Redfern and Martin, 2004), Europa (the moon of Jupiter), Titan and Enceladus (the moons of the Saturn) (Coustenis et al., 2009). According to the research carried out by the NASA, Enceladus is the most habitable place in our solar system other than the earth.

So, we can say that, though we don’t have any strong evidence for the existence oflife in other planets of the Universe, we cannot say strongly that we are the only civilization in the Universe.

3: In order to understand fully the origin of life we should first concentrate on the evolution process that resulted in the formation of complex molecules and in turn the formation of life. According to the RNA world hypothesis, the basis of all the current life is the ribonucleic acid molecules that have the feature of self replication. According to this theory, as the RNA, like the DNA can store genetic information and like protein enzymes, are able to play as catalyst in chemical reactions, they can be considered as the major factor in the cellular evaluation process.

According to one version of the hypothesis, the different nucleotides assemble to form pre- RNA, which was considered as the first molecule that was self replicating and was later replaced by the RNA. On the other hand, the recent studies depict that the prebiotic condition of earth resulted in the formation of only pyrimidine ribonucleotide (Li, Francklyn and Carter, 2013).

The reason behind the development of the RNA world hypothesis is the discovery of several properties of the RNA. These properties include:

Proto-Earth and the Moon

Catalytic activity:

RNA possesses the catalytic activity or the activity of an enzyme also called the ribozyme. The catalytic activities of the rybozyme include-

Helps in the process of RNA synthesis in the ribosome by catalyzing the peptide bond formation in order to produce peptide chains (Lam and Joyce, 2009).

Can catalyze self cleavage with the help of hammerhead ribozyme.

Can induce the synthesis of short strand of RNA with the help of RNA polymerase which is also a ribozyme, the process id also called self replication. The minimum length of the RNA that can be synthesized by this process is 165 bases long (Neveu, Kim and Benner, 2013).

As it is generated from the DNA molecule, the RNA is also the container of genetic information, but the main difference between the DNA and the RNA was based on the stability of the molecule. DNA, being a double stranded molecule is more stable than the single stranded RNA molecule.

All these properties led to the development of the RNA world hypothesis.

As per the hypothesis of the RNA World, during the formation of life, the primordial soup contained nucleotides that were free floating and continuously forming bonds with each other that were primarily unstable. In this way certain base pair sequences were formed that were stable for a considerably longer period of time. These sequences elongate to form the RNA. The hypothesis emphasized on the fact of natural selection in which only the fittest RNA molecules were able to replicate further. The competition resulted in the formation coordination between different RNA molecules that in turn paved the way to the generation of the protocell (Lincoln et al., 2009).

There are various objections related to the RNA world hypothesis. These include-

RNA is a molecule with a complex structure consisting of four different types of nitrogen bases attached to a sugar- phosphate backbone. According to many researchers, this structure is too complex to be formed during the prebiotic period.

The stability of the RNA molecule is very poor due to its single stranded structure compared to the DNA molecule. So, according to the researchers, the formation of stable RNA structure was not possible during the prebiotic period when the temperature was comparatively high.

One of the main reason for the oppose of the RNA world hypothesis is the evidence that for performing catalytic activity, a RNA sequence should be at least 190 base pairs long which was impossible to form during the prebiotic period by random assembly of the nucleotides (Lam and Joyce, 2009).

All these findings along with the studiers of extremophiles suggests that the high temperature of the prebiotic period is not suitable for the synthesis of a RNA molecule, so there must be some other molecules that paved the way of the origin of life.

The failure of the RNA world hypothesis led to the generation of the ‘Proteins First’ hypothesis which emphasized on the fact that either the proteins were synthesized first or both the proteins and RNA evolved at the same time (Francis, 2011). Proteins were found as the most plausible candidate as the studies have shown that the proteins in exptremophiles are resistant to high temperature. So, they may form a stable structure during the prebiotic period of life.

4: The LUCA or the Last Common Universal Ancestor can be defined as the organism, most commonly single celled organism that is reported to live about 3 – 4 billion years ago and it was the common ancestor from which all the organisms have subsequently evolved (Koskela and Annila, 2012). It has been found that the LUCA was decided to be a thermophile. Thermophiles are the microorganisms that are known to line in extreme conditions i.e. in the places of high temperature, as they can grow in that temperature only. From this we can easily conclude that the life originated on our planet in places with high temperature i.e. hot springs etc. Again, in the prebiotic period, the temperature of the Earth was moderate to high, which indicates that at that temperature, it was only possible for the thermophiles to grow.

References:

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Halliday, A. (2006). The Origin of the Earth – What’s New?. Elements, 2(4), pp.205-210.

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Lam, B. and Joyce, G. (2009). Autocatalytic aptazymes enable ligand-dependent exponential amplification of RNA. Nat Biotechnol, 27(3), pp.288-292.

Li, L., Francklyn, C. and Carter, C. (2013). Aminoacylating Urzymes Challenge the RNA World Hypothesis. Journal of Biological Chemistry, 288(37), pp.26856-26863.

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Nemchin, A., Whitehouse, M., Menneken, M., Geisler, T., Pidgeon, R. and Wilde, S. (2008). A light carbon reservoir recorded in zircon-hosted diamond from the Jack Hills. Nature, 454(7200), pp.92-95.

Neveu, M., Kim, H. and Benner, S. (2013). The “Strong” RNA World Hypothesis: Fifty Years Old. Astrobiology, 13(4), pp.391-403.

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