The origin of life on Earth has to be one of the most engrossing queries out there, and also equally significant. Because as important as the origin of the universe and its constituents is, it is because of the origin of life that we are actually in the position to even contemplate it.
And I will acknowledge my ignorance here, for I had always assumed the origin of life must have been figured out and I must have studied about it in school, not really giving much care to the matter.
It was only after a conversation with a friend recently that I realized I didn’t know anything about the origin of life, and all my life I had actually been associating it with another widely taught theory in schools – the origin of species by Charles Darwin.
But now that I have indulged myself in some reading on this topic, I still do not have the definite answer to it. Because guess what, the origin of life on Earth is still a mystery, with a number of theories and speculations surrounding it, some more believable and scientifically backed than the others.
It’s not like we don’t know anything about it, for we do know a lot. We know how atoms came into being first, and how atoms then combined into molecules- the fact we already discussed earlier. We also know how these molecules were able to form into other macromolecules that are considered as the building blocks of life. We know our human body alone is composed of a few elements, the four key elements being oxygen, carbon, hydrogen and nitrogen; calcium, phosphorus, and others in small proportions.
Still, we do not know the definite answer on how the first unit of life was actually created on Earth. And to address more on this topic, I will take a quick detour on another crucial question.
What is life?
Okay, I am not trying to go all philosophical here, and I will try my best not to digress at all, so let’s just go straight into some high school biology.
So, what is life? What differentiates an inanimate object (let’s say a rock) from an animate object (microbes or humans)?
Whenever we think of something animate, two conscious features come to our head amongst a multitude of important activities: Growth and Reproduction (or Replication), both of which is carried out by a basic unit of life known as cell.
For a very long time, the easy answer to the question of how was life first created on earth was – God created it. Even after the discovery of cell, it was considered that these cells must contain some vital force or element that would differentiate the animate from the inanimate.
After it became discernible (thanks to the rise of chemistry) that there is a presence of many chemical compounds in our body, and that cells are responsible for synthesis and processing of these various compounds – called organic because it was thought that only the living organisms could create these compounds, even this ability was attributed to the action of a “vital force” or “life-force” (vis vitalis) that only living organisms possess. Vitalism taught that these organic compounds were fundamentally different from the inorganic compounds that could be obtained from the elements by chemical manipulation. This theory of Vitalism was prominent for a long time.
That would all change with one serendipitous scientific breakthrough!
In 1828, a German chemist, known as Friedrich Wohler, found a way to create urea – a compound otherwise known to occur only in living organisms, in urine – while attempting to create ammonium cyanate, from the inorganic salts potassium cyanate and ammonium sulfate. Thus, the Vitalism theory was duped and it was concluded that life – that is biology – actually rose out of chemistry.
Now, let us try to understand a little chemistry of our biological unit, that is, a living cell.
A living cell is capable of growth, replication, and other number of activities for its sustenance because of the presence of biomolecules. And the two most important biomolecules are the protein and nucleic acids.
Proteins are the building blocks of life, important both for growth (in short, proteins give rise to cells which give rise to tissues and which then give rise to organs), and creation of enzymes that act as a catalyst for important chemical reactions inside the cell (like the breakdown of food to release energy). And these proteins are macromolecules made up of small chemical molecules known as amino acids.
However, only a specific arrangement of amino acids can give rise to protein, and this precious information is present in our other important biological molecule known as the DNA, a type of nucleic acid.
DNA, known as Deoxyribonucleic Acid, simply put is a biomolecule that contains the genetic instructions for the development and function of living things. It carries the genetic code required to make proteins within the cells. So in short, for protein to be created, DNA is a must.
But, here is a twist – DNA itself needs protein for its synthesis and replication. You can’t make new proteins without DNA, and you can’t make new DNA without proteins. So which came first, proteins or DNA. Sounds a lot like the egg-chicken dilemma, doesn’t it?
But hold on, there is more to this chicken-egg situation, there is another type of nucleic acid present, known as RNA (Ribonucleic Acid).
As DNA considers itself all too important, it rather chooses to delegate, and hence copies its information to RNA (in a process called transcription), and this information copied in RNA is then translated to form proteins (in a process called translation). This pattern of information flow is known as central dogma.
Hence, life, in short, is a story of these 3 holy trinity – DNA, RNA, and Proteins – all playing their role inside a cell.
However, we have not yet addressed the elephant in the room, that is, how did this chain first really start? And the answer is – *drumroll* – we do not know. That’s right, while scientists have been working on this over the years and have also proposed some very interesting theories and even discovered some promising results in their research, the quest for a definite answer is still going on.
The widely accepted theory is the RNA World approach, which is basically the idea that the first life consisted of RNA molecules that catalyzed the production of more RNA molecules. The theory was further encouraged after the discovery of RNA enzyme, meaning RNA could act as both the information hub needed to create enzyme and the enzyme itself. This theory is being worked on to this day, and is probably the most scientifically backed and promising theory, with minor breakthroughs throughout the years, but yet no definite proof.
Another theory is the Protein Theory which you can guess by the name itself, suggests that protein came first. But there are no evidences to back it up and is a complete speculation at this point.
And finally, there is also this ‘Out of this Planet’ theory (sounds a bit outlandish, I know) which basically says the fundamentals necessary for the creation of life on Earth actually came from some other planet through some asteroid and evolved here once the condition was favorable.
Therefore, long story short, there is still a mystery surrounding on the what and how of the first self-replicating biomolecule on Earth.
Charles Darwin’s “The Origin of Species” explains how the vast diversity of life could all have arisen from a single common ancestor. But it doesn’t explain the origin of that first single ancestor (which I had wrongly assumed all these years).
While I am usually all in for science and always eager to find out the answers to the ‘why’, ‘how’, ‘’where’, ‘when’ regarding number of subjects, there is a small part of me that wants this to remain a mystery because this gives the possibility to “more”, if you know what I mean. The idea that there is more to what we know today, more room for information, more room for possibilities sort of feels like there is something to look forward to. Not to mention, the mystery surrounding it is kinda, sorta, teensy-bit like living in a fictional world, awaiting a major twist that could come up any day. I apologize, I promised I wouldn’t digress at the beginning, so nevermind on this word vomit of mine, and let’s get back to the topic in hand.
We mentioned in our previous chapter how Earth was far from our habitable home that it is today and was filled with all sorts of toxic and non-friendly chemicals like methane, ammonia, and carbon dioxide. So, how did life actually survive on such adverse conditions, and how did we arrive to this oxygen friendly atmosphere that we have today?
The answer lies in Bacteria.
We’ll discuss more about these bacteria and the evolution of life on Earth in the next chapter.