Throughout history many theories have been proposed regarding the origin of life. One theory becomes adopted by the majority until another more scientific theory is proposed based on research and best guesses. In fact, since none of us were witnesses we will only ever get a theory as the origin of life will remain a great mystery to us. For most of history though, we never questioned the existence of life. It was a no-brainer to those before the 1800’s. Since bible states that God used “the breath of life”, they believed God used a sort of magical power to bring things to life and his magical breath is what separated the living from the inanimate objects. This theory is referred to as vitalism and didn’t involve any chemical or physical forces but purely relied on religious belief. In 1828 Fiedrich Wöhler, a German chemist realized that there were certain chemicals that only were present in living things, such as urea. Wöhler used a simpler chemical, ammonium cyanate, in order to make urea. This showed that the chemicals that were only apparent in living organisms weren't a product of magic but instead derived from simpler chemicals. Even though this was evidence against vitalism, many still fought against any theory that went against the bible. Later on in the 19th century, Charles Darwin proposed his theory of evolution. Darwin proposed that there must be a common ancestor to all life forms. His argument similarly to Wöhler’s created friction between science and the church. Darwin argued that God didn’t create and breathe life into each species individually but instead there existed a primordial organism that evolved into all the different species we see today. Another question still remained; if there was a common ancestor to all living things then where did it come from? Darwin pondered this question, and contemplated whether or not life was generated from a warm little pond. Perhaps under the right conditions in a pond that received a lot of sunlight, organic compounds could combine to create some sort of protein that could then evolve further. Darwin’s theory was a breakthrough in the mystery of the origin of life and jumpstarted more scientific research on the topic.
In 1924, Alexander Oparin of the USSR published a book called “The Origin of Life.” Oparin’s theory was evidently similar to Darwin’s vision of the warm little pond. He envisioned an earth that consisted of a molten hot entity that space rocks collided into, giving the earth structure. These rocks aided in cooling the earth to a temperature that allowed for condensation of water vapor. Most importantly, Oparin stated that the rocks had a large variety of chemicals with a high concentration of carbon. Riffing off of Wöhler’s research regarding simple chemicals combining to form more complex ones, Oparin believed the process occurred in water. To support his theory, Oparin observed, coacervates under a microscope and realized that their behavior mirrored living cells. Since organic chemicals in contact with water can form these “life-like” coacervates, Oparin believed that essential biomolecules such as amino acids were formed in water. He noticed these coacervates could absorb surrounding chemicals and grow. This led to his claim that these coacervates were the origin of life. The greatest flaw to Oparin’s theory was that these complex chemicals would have been destroyed by oxygen quicker than they were made. Was there no oxygen present in the atmosphere when Earth was created?
Stanley Miller joined forces with Harold Urey in 1952 to put Oparin’s theory to the test. In their lab they set up glass flasks with water and gasses that would have been present at the time earth was formed. The gasses consisted of ammonia, methane, and hydrogen. They ran electricity through them, giving each flask shocks to mimic the frequent lightning that would have occured. The clear water was noticeably changed hours after. The color had turned pink and then a darker red by the end of a weeks time. This visually displayed that other chemicals had formed in the flasks. The contents of the flasks were then analyzed to see exactly which compounds were created. Amongst other chemicals, two amino acids, alanine and glycine, were present. This discovery led Miller and Urey to support and validate Oparin’s theory. Later on, scientists proved the contents in the flasks to not only consist of the two amino acids that were reported but twenty amino acids total. Building blocks of life were proven to be created in an environment that mimicked the atmosphere at the time the earth was created. This experiment, the Urey-Miller experiment, was a huge breakthrough in the mystery of the origin of life but it still wasn’t the answer by any means. The complex chemicals synthesized in the lab still weren’t as complex as our living cells. The search for a common ancestral cell continued.
In order to understand how a living cell could have been created from scratch, we needed to know more about how cells operated. Scientists found nucleic acids like deoxyribonucleic acid in living organisms. At the time, they believed that proteins contained genetic information as opposed to DNA since proteins appeared as more complex biomolecules. In 1952 Alfred Hershey and Martha Chase took a look at viruses. These viruses contained protein and DNA and they introduced them to bacteria. They came to the conclusion that viral DNA entered into the bacteria, not the protein. Therefore proving that DNA contained the genetic material and not protein. Deoxyribonucleic acid must be passed on from parent cells to the next generation. The way DNA copies itself to do this was discovered by James Watson and Francis Crick. They proposed a double helix structure of DNA that consists of four nucleotides, Adenine, cytosine, thymine, and guanine. This structure would then allow for unwinding of the double helix to then copy the DNA using each template strand. Since genes are passed down from parent to children cells there must have been one common ancestor that passed it’s genes on to another cell and so on. During transcription, RNA segments are created to then travel to the ribosome for translation into proteins. Every living cell uses the mechanism of DNA to RNA to ribosome proteins but how did they all come together to form this intricate process? Chemist, Leslie Orgel, suggested that life’s common ancestor didn’t have DNA or proteins but only RNA instead. This meant that this first organism’s RNA was able to replicate itself. Watson and Crick had already proposed a mechanism for DNA but Orgel thought, why couldn’t RNA copy itself in the same manner?
Leslie Orgel suggesting that life began with RNA may have been the key to the origin of life on earth. There are major differences between RNA and DNA that could actually support Orgel’s theory. Since RNA is single stranded opposed to double stranded DNA molecules, it can fold similarly to proteins. Since proteins can fold in various ways and make enzymes maybe RNA could do the same. If RNA could create enzymes to catalyze chemical processes then it could have been the original biomolecule. A biochemist by the name of Thomas Cech discovered that a section of RNA from a simple organism, Tetrahymena thermophila, seemed to detach itself. He experimented with this phenomenon by getting rid of all enzymes that could have potentially been cutting the strand. The strand kept becoming detached and after analyzing what was going on Cech determined that he had found an RNA enzyme. This discovery proved the ability of this single stranded molecule to form enzymes. It supported the theory that this was an RNA world to start. A physicist, Walter Gilbert, wrote a book titled “Walking in Nature”. In this book, Gilbert supports Orgel’s idea of an RNA world at the origin of life. He explains how he believed RNA was a molecule that could store genetic information as well as catalyze chemical reactions. Basically, in this simple organism RNA did the work that many biomolecules are known to do in living cells today. A key biomolecule that supports the RNA world theory is the ribosome. This is due to the ribosome being based on RNA. As technology enhanced, scientists were able to take better quality pictures of molecules and examine their structure. Examining the structure of ribosomes it became apparent that their catalytic core was RNA. Ribosomes are necessary in all living cells and was shown to are derived from RNA.
Although many scientists were doing all they could to justify the RNA world theory, it still had it’s major flaws that nobody could answer. In order for RNA to be the origin of life it would need to self replicate and even if it could, how could it perform all the functions that many other biomolecules are needed for? There were efforts made to create RNA that was self replicating but every experiment failed. RNA on its own was more than difficult to synthesize from nothing. It’s difficulty also didn’t support the theory that there was just an RNA molecule out there created from scratch. The RNA world could be