There are many theories as to how life got its start on Earth. Whether it was by intelligent design, evolution, comets or space aliens—the same problems tends to pervade each hypothesis. The first problem (with theories such as evolution) is the very beginning of life. Sure, evolution accounts for every subsequent stage, but how indeed was the first life form created? And the second problem is the probability factor of any theory. For those such as space aliens or even intelligent design, there is no proof of the cause itself, much less a way to determine if it really was the cause of life. Other theories are more susceptible to such ponderings. So was life probable or not, and how so? These questions are at the heart of any scientist seeking to find the origin of living existence, and rightly so.
First, let us consider the theory that Harold Urey and Stanley Miller researched. “They passed an electric discharge through the flask containing the atmosphere to simulate lightning … After a week, Urey and Miller … found that the water contained large amounts of amino acids, … nucleic acids, sugars, and fats.”[i] This experiment demonstrated that it is not in fact impossible to create organic compounds from inorganic ones, given the right conditions. And, according to Panno, “Given the conditions of that period [prebiotic Earth], it now seems almost inevitable that such molecules would be synthesized.”[ii] This experiment, however, does not provide an example of how this organic matter could have replicated itself, not even mentioning creating living cells. To begin countering this flaw, another hypothesis is coupled. Since neither DNA nor proteins can both replicate and catalyze reactions simultaneously, scientists proposed that most of the matter created by these random lightning storms was RNA, which can perform both functions. “Ribozymes [an RNA molecule capable of enzymatic activity], assembled in the prebiotic oceans, could not only replicate themselves but also could have catalyzed the formation of specific proteins, which in turn could have functioned as structural proteins or enzymes.”[iii] So we have one hypothesis that states that organic matter was created from inorganic matter by random lightning bolts, and another that says that RNA became the dominant molecule of this organic matter. This still does not address the question of how actual cells came into being, as well as others. Before this adventure delves even deeper into improbability, a different opinion is called upon.
Though one of the mainstream theories, this Urey-Miller series of hypotheses may not be at all likely. The Scientific American explains that “In recent years … researchers have envisioned that life’s ingredients might have accumulated in … rocks, like gray volcanic pumice, [which] are laced with air pockets created when gases expanded inside the rock while it was still molten. … Given enough time and enough chambers, serendipity might have produced a combination o fmolecules that would eventually deserve to be called ‘living.’”iv Hazen goes on to explain many different ways in which minerals could have helped creating a stable beginning for life. In addition to creating pockets for cells, rocks could have acted as scaffolding in layered minerals that prevents the breakup of large molecules in early-earth conditions, and participated in vital reactions, such as crystal lattices aligning amino acids to form peptide bonds.
The iron-sulphur mineral bubble theory is a very convincing candidate for the origin of life—not only because it explains previously unanswered questions, but because it is very probable, and we once again turn to
“Think about what is happening here. Such conditions could not have been rare on the early earth. … Volcanic seepage sites must have existed across much of the surface of the earth. … The formation of many millions of tiny cells, bounded by iron-sulphur membranes, requires no more than a difference in redox state and acidity between the oceans and the volcanic fluids emanating from deep in the crust—a difference that certainly existed. … UV rays [from the sun] split water and oxidize iron … The ocean becomes gradually oxidized relative to the more reduced conditions in the mantle. According to the basic rules of chemistry, the mixing zone inevitably forms natural cells, replete with their own chemiosmotic and redox gradients.”vii
These conditions are not only probable but they must have been in constant existence, unlike the fragility of something like a primordial soup or an RNA world. And if all the cells really need is an ATPase in the iron-sulphur membrane, it would be easy to imagine that perhaps more than one such bubble trapped this essential protein from the environment created by a Miller-Urey type of process, and was able to begin respiration and other chemical reactions that would eventually lead to life itself. With the iron-sulphur mineral bubble theory, I can now reasonably conclude that the appearance of processes performing chemical reactions that aid to propagate the same processes (which is one of the definitions of early life) was probable, if not inevitable on the early earth.
[i] Panno, Joseph. The Cell. Facts on File, Inc. 2005, p. 4.
[ii] Ibid.
[iii] Panno, Joseph. The Cell. Facts on File, Inc. 2005, p. 11.
iv Hazen, Robert M. “Life’s Rocky Start.” The Scientific American, 2001, p. 79
v Lane, Nick. Power, Sex, Suicide: Mitochondria and the Meaning of Life.
vi Ibid., p. 98.
vii Ibid., p. 103
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