FEATURES BIOLOGY
The origins of life Vanessa explores the age-old question of where and how life came about. Tsui, SFC1 You go into the shower and this thought springs into your mind: "How did I come into existence?" At first the answer seems obvious to you: you were birthed from your mother. But what about before her? What starts the evolution of complex organisms, or even simple organic life itself? Scientists have been trying to answer this question for years. While not entirely dismissing the possibility of extra terrestrial origins, they might have come up with some theories in the past century.
In the beginning... In the 1920s, two scientists, J. B. S Haldane and Alexander Oparin theorised that life may come from a ‘prebiotic soup’ or a primordial soup; they imagined the early ocean was rich with complex molecules produced by natural chemical reactions. In this soup, further reactions can take place, eventually producing living cells. This speculation actually dates back to 1871 when Charles Darwin wondered if life could have formed from o ina L chemicals "in some warm little y Reg Ill u s t r a ti o n b pond". It is thought that about 4 billion years ago was the earliest possible time that the first life could emerge on Earth, a period called the habitability boundary. Fossil evidence shows that microbes existed about 3.7 billion years ago, known as the biosignature boundary. At some point between the habitability boundary and biosignature, non-life became life. This miraculous arising is what scientists call Abiogenesis. But what is life? At school, we learn MRS C GREN, the checklist for the characteristics of life of what we know today. The earliest life, however, is a lot simpler. The definition for life is so vague that many scientists refuse to bother with it. In 1944, however, Schrödinger defined life as ‘a struggle against entropy, the persistent resistance to decay, the preservation of disequilibrium’. That is to say, a thing is considered alive when it fights for survival, and it also means that life will constantly evolve to better adapt to survive.
‘A struggle against entropy, the persistent resistance to decay, the preservation of disequilibrium.’ 19
The soup of life Going back to the primordial soup, Darwin’s and Oparin’s ideas were only speculation and not legitimate hypotheses since no one could find a way to test or observe them back then. In 1953, two other scientists called Stanley Miller and Harold Urey tried to replicate the formation of life by simulating early Earth conditions in the lab and carefully watching what happened. They designed a water apparatus to model the ancient ocean and gently boiled to mimic evaporation. Along with water vapour, they chose methane, hydrogen and ammonia as the gases in the atmosphere. As a source of energy, they added electrical sparks using 2 metal electrodes to simulate lightning. Their goal was not to recreate life, but to test the first step of Oparin’s model - can simple chemistry naturally give rise to the complex molecules of life? After running the experiment for a week, their ocean became brownish-black. Careful analysis revealed that many complex molecules indeed formed, such as amino acids (the building blocks of life) which were previously thought to only be produced inside our bodies. However, scientists later criticised this model because they couldn’t know for sure if the gases used by Miller really were the most common gases of the ancient earth. Because of this, many other simulations have since been done to show that the molecules of life can form in a wide range of environments, including hypothermal vents or on the earth with the help from the sun’s radiation.
The experimental set up for the Miller-Urey experiment. Image credit: "Miller and Urey's experiment," by CK-12 Foundation, CC BY-NC 3.0.
