An Exploration into the Origins of Life
Image from Freepik
Where does life on Earth come from?—A question that has been asked by humans throughout history, from the youngest of kids to the most educated of adults, it has troubled our curious minds since antiquity. However, generations upon generations of scientists have slowly chipped away at this mystery with their endless hard work through experiments, exploration, and research. Indeed, though the question has not been fully answered, much more is known today about life’s origin than when people first began pondering about our past.
Though religion may have its own answer to this pivotal question, modern science generally explains that life arose from nonliving matter in a process termed abiogenesis. Once the first matter was introduced to the universe, whether explained by the Big Bang or some other theory, abiogenesis describes the formation of increasingly complex organic molecules essential to life from the most common of elements and compounds. Then came the formation of macromolecules, subcellular components, and finally, cells, the fundamental unit of life. Our current understanding of the Earth’s history states that the planet formed over 4.5 billion years ago (bya), while life emerged over 3.5 bya, meaning that the process of abiogenesis—if it had happened entirely on Earth—must have occurred in the first billion years of our world’s existence.
Image from Encyclopædia Britannica
In the 1920s, British scientist J.B.S. Haldane and Russian biochemist Aleksandr Oparin introduced separately the idea that the simple gases present in the atmosphere of early Earth, when supplied with external energy such as ultraviolet radiation, could have formed the organic molecules necessary for creating and sustaining life. This has come to be known as the Haldane-Oparin Theory. Then, in 1952, American scientists Stanley Miller and Harold Urey at the University of Chicago successfully demonstrated the production of amino acids, the building block used by all life forms to create proteins, under conditions meant to mimic that of primitive Earth, from about 4 to 3.5 bya. As shown in the diagram above, a mixture of simple gases thought to have existed in the atmosphere at the time—methane (CH4), ammonia (NH3), water vapor (H2O), and hydrogen (H2)—were supplied in one flask with sparks, simulating lightning, while another flask containing water was boiled, simulating the oceans. Two sets of tubes connected the two flasks: one for water vapor to be continuously supplied to the upper flask and the other to pass the gas mixture through a condenser and into a trap for the collection of liquid samples. After running the set-up for one week, the researchers analyzed the samples and discovered several amino acids, including glycine and alanine. Scientists performed numerous similar experiments in the subsequent decades, testing various other sources of external energy and successfully producing over 30 different amino acids, encompassing more than half of the 20 amino acids present in all living organisms on Earth. Since amino acids could have reacted further to form increasingly complex molecules, all of these experiments have provided evidence supporting the theory that abiogenesis could have created the earliest forms of life from inorganic gases in the primitive atmosphere.
However, Earth is not the only location where scientists believe abiogenesis could have occurred. Just as our own planet contained simple gases and sources of energy input, other locations within the universe did as well and it is just as likely for life to have developed on other planets or celestial bodies. The theory of Panspermia—developed by scientists including Jöns Jacob Berzelius, Hermann Richter, and Svante Arrhenius from the early 1800s to 1900s—states that once life developed someplace outside of Earth, meteorites, comets, or asteroids distributed simple life forms, such as bacteria, to Earth sometime in the first billion years of the planet’s existence. This is consistent with the geological history of Earth. Specifically, the events of the Late Heavy Bombardment occurred sometime from about 4.5 to 3.8 bya and was characterized by a continuous barrage of asteroids and other celestial objects against the young planet for 20 to 200 million years. In fact, the Late Heavy Bombardment is thought to have first introduced water to Earth. The endless possibilities of abiogenesis within the vast confines of outer space, coupled with the remarkable circumstances of our planet’s early history, make Panspermia appear viable despite its relative lack of supporting evidence. Furthermore, developments in the past few decades, such as the discovery of organic molecules throughout the Milky Way Galaxy and experiments proving the ability of biological samples to survive in the harsh conditions of space, have brought Panspermia back to the forefront of scientists’ minds.
Whether abiogenesis occurred on Earth or outer space, or whether it even explains the origin of life, remains an unsolved mystery. Despite centuries, even millennia, of research by scientists, we as humans still know only very little about our own history and the universe’s history. So, where does life come from? Perhaps, we may never know for sure. But, it is human nature to be curious, and as long as we still exist, our endeavor toward answering this momentous question will never cease.
