We have all heard the theory that life originated under the water. The words ‘primordial soup’ have probably come up a few times. But what does that mean? Surely a human baby could not have just appeared below the surface! No, life emerged slowly over eons of continued evolution.
It was once believed that cells and organisms simply appeared into existence. This theory of spontaneous generation was disproved by Louis Pasteur’s Swan Neck Flask experiment. He stated “Omne vivum ex vivo” or “Life only comes from life”. However, from this arises a simple question: Where did the first cell come from? In 1924, Russian Biochemist Alexander Oparin published a book titled “The Origin of Life” in which he theorised the systematic development of living cells from simple chemistry. He thought of the early conditions on Earth’s oceans to be a ‘primordial soup’ containing a collection of complex molecules produced by chemical reactions.
In the 1950’s Stanley Miller and his professor Harold Urey put this theory to the test. Together they designed an experiment to simulate the prehistoric water cycle. In a closed glass vessel they combined water (gently heated to simulate volcanic activity); methane, hydrogen and ammonia (gases believed to be present in the atmosphere at the time); and sparked electricity through the gases (to simulate lightning). After a week, they found that complex molecules such as amino acids and hydrocarbons had been produced through a series of chemical reactions. Once this was proven, we could infer that simple organic molecules such as RNA and DNA - the genetic material for all living things - were also synthesised similarly about 3.7 billion years ago. Soon after, the formation of an isolated internal environment in the form of membranes, to package the organic molecules ensured that an optimal environment was maintained, so that important processes such as replication and catalysis could take place. And with that, the first cell was born.
As recently as two billion years ago, some cells began to develop specialised functions and multicellularity evolved. The origin of such eukaryotic (plant, animal, fungi and protist) cells can be explained by the Endosymbiotic Theory which posits that a smaller prokaryote (single celled microorgansim such as bacteria and archea) entered a larger one and instead of being digested and absorbed, the two cells formed a mutually beneficial, symbiotic relationship. The evidence for this theory can be found in cell organelles such as the mitochondria and chloroplasts. Thus life as we know it began.
In this way, scientists have gradually built upon previous knowledge and used past theories to reach the current comprehension of our origin. We still have a long way to go in terms of our understanding of how we came to exist, but in the light of new ideas and perceptions we seem to be headed on the right path!
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