“Life, uh, finds a way…”
September 12, 2010 Leave a comment
Dr. Ian Malcolm says it all in this classic Jurassic Park quote. Life does find a way on Earth. We have found life on almost every single inch of the planet, even the darkest, hottest, most horribly adverse environments on this tiny blue rock have some type of life thriving there. But no matter how much science we study, no matter how deep our understanding of the universe and biological systems becomes, there’s still a lingering question: How did this life begin?
Scientists who study “abiogenesis”, the formation of life on Earth, have three basic hypothesis for how life may have begun on Earth. The first is the idea of “panspermia”, the idea that microscopic organisms were transported to Earth from space by means of an impactor such as a comet or asteroid. The second is the theory of “spontaneous generation”, the idea that life just spontaneously began from non-life. The final theory is “chemical evolution” where it is believed that life arose from non-life by gradually building complex structures from simpler ones. The idea of spontaneous generation is pretty much a long-shot, the fact that it could have just randomly happened is analogous to the fact that there’s a minute (close to, but not technically zero) possibility that your atoms could pass through a wall if you run into it. Some scientists believe that a catalyst, such as lightning or some other naturally occurring high-energy phenomena, may have transferred enough energy to ignite the “spark” of life, but the idea that all the correct criteria for life just happened to spontaneously occur seems far-fetched. There’s probably about a 50/50 chance on the panspermia vs. chemical evolution debate, but in either case the development of complex life forms happened in four steps: 1) small organic molecules develop from Earth’s original materials and/or via panspermia, 2) these small molecules combine into long chains for living systems, 3) these long chains form isolated, reproducing systems, 4) these reproducing systems evolve and diversify into species of plants and animals.
In the 1920s, Alexander Oparin came up with the idea of a “primordial” or “primeval soup” of organic compounds that could be driven to evolve chemically by sunlight. The idea was that at some point early on in Earth’s evolution small tide-pools of basic chemical compounds were formed; sunlight then provided energy that fueled chemical reactions between the water and organic molecules to form “coacervate droplets” or droplets which encapsulated the organics within and separated them from the surrounding water. Oparin proposed that these droplets then grew by fusing with other droplets and reproduced through fission. In the ’60s, Oparin’s theory was furthered by Sidney Walter Fox, who realized that phosphoric acid in early Earth’s atmosphere catalyzed the process that turned amino acids into proteins; in his lab he was able to use phosphoric acid to produce protein-like molecules called “proteinoid microspheres” from amino acids.
So what happened, life was either deposited on Earth from somewhere else in the galaxy (who knows where!) or conditions on Earth were favorable enough to allow naturally occurring chemical processes to evolve into life. Although science supports it, the idea that non-living matter can just transform into living organisms is a little hard to comprehend, but it happened. It must have. Even if life didn’t originate here on Earth, those transplanted organisms must have started somewhere. Of course, as far as we know, Earth is the only place life exists. In our limited exploration of the solar system, we haven’t found any life, although we have some ideas where life could be found (Titan, Europa, Triton, Jupiter’s upper atmosphere) or perhaps where it could have existed in the past (Mars). But if life exists on these worlds, even primitive microbial life, it might be very different than the water-based organisms we find here on Earth, it could be methane-based or sulfur-based? Who knows? But how did it form? How did we form? I have no idea, but I’d love for us to find out.
(Some content of this post was derived from notes taken of lectures given by Prof. Thomas Bania during AS117- Cosmic Evolution taught at Boston University in Fall 2009.)