Introduction

The question of how old the earth really is arose sometime in the steemstem discord channel. It was shocking to hear that even some well renowned geologists thought the earth was just 6000 years old. That is absolute bonkers and well, people choose to believe anything these days.

The earth has been shown to be not less than 4.5 billion years old and this was known and proven 65 years ago. Life however was shown to originate a billion years later. Fossil records have been able to prove when life possibly began on earth and that had created little or no room for argument. But one difficult question to answer has remained.

How Exactly Did Life Begin on Earth ?

Charles Darwin gave a little hint when he said that life possibly started in a “warm little pond” consisting of a vast majority of elements necessary for the formation of life. Darwin however focused more on evolution (His works which were amazing and define modern biology in a lot of ways today) than he did on the origin of life.

When it comes to the question of the origin of life, several hypotheses have been put forward. Everything points to the origin of the first cell and in more specific terms, the first biomolecule essential for life. Religion and Philosophy take similar stance on the origin of life in that they both believe life to have originated as a result of supernatural events which cannot be explained by science. We are just asked to believe by religion there’s a guy out there who utters magic words, orchestrate supernatural events and boom, we have the earth. Philosophy tells us the origin of life is beyond our understanding.

But as a supporter of facts over fiction, I’ll like to bring to light what science (which hugely relies on facts) has to say about the way life originated. There are a lot of hypotheses as regards the origin of life from a scientific perspective. The first hypothesis was bullshit imo but it was quite funny that people actually believed it for some time. This is theory of spontaneous generation.

Aristotle proposed this and for two thousand years, it was seen as a fact. The theory of spontaneous generation proposed that organisms could arise from inanimate matter. This was seen where cheese was kept in a bag and days later, mice were found in the bag and this eventually made people believe mice could be generated from cheese (absolute bonkers). It was also seen where maggots were seen on dead flesh and people also assumed maggots came from decaying meat.

The 1668 experiment by Francesco Redi disproved the misconception that maggots came from decaying meat. Redi made use of three jars with controlled experimental conditions. In the first jar, he placed decaying meat and made sure to leave it open. In the second jar, he also placed decaying meat but covered it with a guaze making sure air could have access to this jar but not flies. In the third jar, a placed decaying meat and completely sealed it. The results he obtained were quite remarkable.

In the first jar, maggots could be found on the decaying meat in the jar. In the second jar, flies were observed to lay maggots on the wire guaze but the maggots were not found in the jar. In the third jar, the were no maggots either inside or on top of the jar as the flies could not even tell that there was indeed decaying meat in the jar since it was properly sealed. This quickly disproved the idea that maggots originate from flesh as if it this was the case, the maggots would be seen in either the second jar (aerated condition) or the third jar (non-aerated condition) or even both.

Redi’s experiment was a step forward for science but people still thought that his results might not hold true for microscopic organisms like bacteria which they still chose to believe could come from inanimate matter. Louis Pasteur made sure to debunk this in his famous experiment in 1859. Louis Pasteur was of the opinion that the cells found in the dust in the air carried bacteria that contaminated broth so the bacteria wasn’t formed in the air itself as was widely thought then. Louis Pasteur collected broth, boiled it for an hour to sterilize it (making free of microorganisms) and decided to present them in three different sterilized jars.

The first jar was left open to allow air enter into it. The second jar was plugged with Cotton to allow air to be filtered of bacteria. The third jar was connected to an S-shaped tube for easy observation of the dust particles which will collect in the tube. The results he obtained were amazing. The first jar was cloudy showing that it has been infiltrated by bacteria. The second jar remained sterile as the cotton plug was able to filter bacteria out. The third jar refuted all earlier claims totally as dust particles which contained bacteria was observed to be collected on one end of the S-shaped tube and since the dust could not rise against gravity, bacteria could not gain access to the broth in the jar and broth remained sterile. Louis Pasteur ended on this experiment on this note:

Never will the doctrine of spontaneous generation recover from the mortal blow of this simple experiment. There is no known circumstance in which it can be confirmed that microscopic beings came into the world without germs, without parents similar to themselves. - ^Wikipedia.

It was indeed a win for science as the theory of spontaneous generation was totally disproven. The next hypothesis on the origin of life suggests that life came from the extraterrestrial world. In more specific terms, Life was as a result of spores being carried across planets to the earth. These spores contained elements which could combine readily reacting and leading to life ultimately. This is known as Panspermia. A chief proponent of this idea was Svante Arrhenius but this idea could be traced back to fifth century B.C. where the Greek philosopher Anaxagoras proposed that the universe was made up of seeds which could give rise to life on getting to earth.

Arrhenius made a clever attempt at explaining the origin of life however when he proposed that spores could shuffle between planets by pressure from radiation. This seemed plausible till it was found out that bacteria spores could not possibly survive the radiation it could possibly be exposed to in space. This theory was even further killed by the theory of the primordial soup which was brought to light by Alexander Oparin. This is the fourth possible hypothesis of the origin of life on earth and it is the center of my discussion.

Aleksandr Oparin’s Take on The Possible Origin of Life

Oparin’s hypothesis was made to answer the question; How were the first biomolecules synthesized ?. Looking at the complexities of biological pathways, one would expect the synthesis of biomolecules from simple aggregation of molecules to be nothing short of impossible but the opposite has proven to be the case.

Oparin suggested that the prebiotic earth (the earth before the existence of life) had a reducing atmosphere and this atmosphere made it possible for biomolecules to be formed as a result of certain chemical reactions. The Earth’s atmosphere was believed to be abundant in hydrogen, methane and ammonia. On exposure to lightning or heat from volcanoes, these molecules could form different organic molecules which dissolved in seas that formed the primordial soup.

Over time, these organic molecules react forming complexes. These complexes would go on to form membranes and enzymes which are known to precede cells. It is important to note that Haldane’s hypothesis was quite similar to Oparin’s (and yes Oparin’s came first but Haldane did not plagiarise anyway :p) and came to light at the same time. Haldane even coined the term Primordial Soup.

Oparin and Haldane were Deemed Crazy till Miller and Urey Had to do one for the culture.

In 1953, Miller under the supervision of Urey simulated the hypothetical prebiotic earth conditions in a laboratory. They passed electricity which would represent lightning seen in the prebiotic earth through a solution containing methane, ammonia, hydrogen. The resulting products were amino acids which could easily be observed. The specific amino acids were glycine, glutamic acid, alanine and leucine. Adenine could also be produced from hydrogen cyanide while Ribose from formaldehyde under prebiotic conditions. This would mean the RNA could be formed.

The Chicken or Egg Question in Biochemical Evolution

Over the course of time, the question of the egg or chicken which came first has been asked but we all know the chicken came first. The question in biochemical Evolution is analogous but quite different. The RNA or protein which came first ?

While the RNA world hypothesis argues in favour of RNA, the Protein World Hypothesis argues in favour of proteins. The RNA world hypothesis is the most acceptable theory of abiogenesis.

This hypothesis suggests that RNA acts as both an information repository and a catalyst. RNA acting as a unit for storage of biological information ruled out the need for DNA in the primordial soup. This was a bit hard to swallow as DNA is a more stable material for storing genetic information since it is more resistant to degradation by chemicals and other agents of degradation. But there’s an explanation to make RNA acting as a unit for storing genetic information much more plausible.

In the primordial soup, RNA was continually being formed and only the most stable and most catalytic RNAs were continually synthesized. The weaker ones stopped being synthesized to encourage the formation of more stable RNAs. A process aided by natural selection. So this meant that RNAs with methylated backbones (which will be much more stable) were being synthesized in the process since synthesis of these RNAs was solely down to chance and completely random.

The argument that RNA was the catalytic agent in the prebiotic earth is strongly supported by the fact that RNA could catalyze the replication of its own molecules. In other words, the RNAs were self replicating. Proteins didn’t and do not have these abilities so it wouldn’t make sense for them to act as catalytic agents since they will not be available in sufficient amounts to carry out the level of catalysis required at that time. Well, these are all just arguments but they make sense to me and hopefully, to you too. We can’t conclusively say if the RNA came before the protein but right now, the argument is in favour of the former.

DNA and proteins took up the genetic and catalytic roles of RNA in present times and this makes sense as DNA has shown to be much more stable than RNA so it would only make sense to pass on information in a more stable molecule. Proteins have shown more versatility as compared to RNA and are even capable of catalyzing much more reactions with varying substrate specificity. This would explain why proteins had to take up the catalytic role of RNA.

We had the RNA, Then The Proteins, The Cells Were Next ?

Lots of reactions taking place in the primordial soup led to the development of the earliest cells. Noticing that the earth was made up of chemical substances mostly, one would expect the cells in this era to be capable of utilizing these chemicals. Well, this was the case. The earliest cells were referred to as chemoheterotrophs as they were not adapted to synthesizing chemical molecules(which they didn’t need to in practical same) and were well biologically engineered to utilize molecules synthesized from their environments.

They however evolved as they began to find ways to synthesize these molecules themselves and got more independent of their environments and that led to the development of the chemoautotrophs. Photosynthetic pigments evolved in these cells and they could fix carbon dioxide using energy from sunlight and produce glucose although they used hydrogen sulfide (H₂S) instead of water (H₂O) as an electron donor since this was a reducing atmosphere. With time, molecules capable of utilizing water as electron donors eliminating oxygen as waste evolved and that led to the development of a more oxidizing atmosphere. The Cyanobacteria were the earliest to show this ability. With the release of oxygen into the atmosphere, the anaerobic bacteria population declined while the aerobic bacteria population prospered.

The eukaryotic evolved from the prokaryotic bacteria about 1.5 billion years ago. The need for more DNA coupled with the desire to package DNA into more compact structures like chromosomes gave rise to the need for eukaryotic cells. There was also a need for compartmentalization to separate several biochemical processes and this also gave rise to the need for more eukaryotic cells since they possess membrane bound organelles and would largely help the compartmentalization process. Some eukaryotic cells would go on to form endosymbiotic relationships with certain prokaryotic cells conferring on themselves the ability to produce oxygen and also undergo photosynthesis. Some aerobic bacteria practically became mitochondria while cyanogenic bacteria became chloroplasts.

Going through time, cells found it more biologically profitable to work together gaining more advantage than their competitors who survived alone as specialization arose and these cells acting as a team could focus on and enhance different processes necessary for life. They became faster and reproduced more. These cells eventually began to exist as colonies and this subsequently lead to the evolution of more complex organisms that could carry out different functions necessary for life. Basically unicellular organisms became multicellular organisms.

The Genetic Code: What it can Say About Evolution.

The Genetic code is universal as it applies to almost all organisms so evolution can be observed by looking out for mutation in certain gene sequences. Mutations can occur in certain genes in producing variation which is a requirement for evolution and making the most genetically fit species thrive. The mutations occur at the molecular level but the changes that follow can be observed morphologically. It could be the deletion or addition of a single nucleotide or the substitution of one nucleotide for another. Whatever the case may be, different proteins are synthesized and the consequence may be biochemical evolution.

Summary

Biochemistry has given its two cents about the possible origin of life but this still leaves lots of questions of unanswered. The evolution of life has been properly justified however and the fossil records are there to back that up.

References

Origin Of Life: Issues. Retrieved on June 2nd, 2018.

The Origin of Life: Hypotheses of Origins.Retrieved on June 2nd, 2018.

Spontaneous Generation.Retrieved on June 2nd, 2018.

Abiogenesis.Retrieved on June 2nd, 2018.

Lehninger, A. L., Nelson, D. L., & Cox, M. M. (2000). Lehninger principles of biochemistry. New York: Worth Publishers. pp. 31-38.

Berg, J. M., TyMoczko, J. I & Stryer, L. (2002). Biochemistry (5th Edition). New York. W.H. Freeman. pp. 57-79.

Pratt, W. C & Cornely, K. (2014). Essential Biochemistry. (3rd Edition). Wiley Publishers. United States of America. pp. 14-18.

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