Abstract
The origin of life, a multifaceted question arguably as old as time itself, has baffled humanity for as long as it can recollect as a society, raising icy, out of this world, and shocking theories about the creation of complex arrays of life from inorganic compounds. It is essentially the classic “something from nothing” question, leaving scientists at various dead ends that call for experiments on and studies about Early Earth’s atmospheric, aquatic, and geological conditions. Resultantly, it has raised seven major theories which all attempt to—and for a good reason—explain how the aforementioned “something from nothing” phenomenon can even birth such a remarkably sophisticated thing: life. However, while all seven controversial theories are supported by logic and valid reasonings, the question is now about which one or which combination of theories is more feasible. That said, scientists must acknowledge the informational narrative that characterizes and instructs living systems, thereby necessitating a crucial focus on context-dependent causal factors for the emergence of life as the one force connecting all seven theories is the informational system upon which to connect all seven theories all life on Earth depends.
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Throughout Earth’s ~4.5 billion-year history, there have been major climatic and geologic cascades of events that life had to face to evolve into the complex, energy-dependent information systems that they are today. That said, the first question to answer is where the energy needed to catalyze specific biochemical and/or metabolic reactions came from, so scientists have proposed that lightning, possibly a quintillion of lightning bolts spurred by the geological chaos of Earth’s formation, were able to provide enough energy for Earth’s genetic code. There is, however, one significant discrepancy with this proposition: what was the recipient of this energy? To answer that question, scientists required an assessment of the causal architecture of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). They are composed of pentose sugars (deoxyribose and ribose, respectively) and nucleic acids, or nucleobases. In addition, these pentose sugars and nucleobases are held together in a double-helical structure (in DNA)—or a helical structure in RNA—by phosphorus which functions as the genetic code’s backbone. It is also the star of the show when it comes to ATP (the predominant means of energy transfer) and intracellular structures, including organelles such as the smooth endoplasmic reticulum and fluid intracellular/extracellular barrier known as the plasma membrane. However, phosphorus was an elusive element 3.5 to 4.5 million years ago, so, again, where did it come from?
Five years ago, the geology department at Wheaton College received a call from a family in Illinois reporting a small fire caused by what was supposedly a meteorite that ‘landed’ in a family’s backyard. The family also reported a weird rock embedded into the dirt; however, Benjamin Hess, an undergraduate at Wheaton and now a graduate at Yale University noted that “Meteorites, contrary to popular belief, are cold when they hit the ground” (Greenfield, 2021). As a result, test samples unveiled an ingredient for life previously believed to have come primarily from meteorites: fulgurite. Fulgurite is a lightning-induced clump of glassy minerals, and it acts as a significant source of prebiotic, reactive phosphorus. Even though it is prevalent in its abiotic, oxidized state (PO43-), it can also be found bound to minerals at different oxidation states. For instance, in the below statement, from the journal titled Nature Communications, Article Number 1535 (2021), the reactivity of phosphorus at different oxidation states revealed lightning’s potential as a catalyst for the development of phosphorous, which can freely interact with organic compounds, such as nitrogenous bases and pentose sugars:
“[R]educed phosphorus such as phosphide (P0) in the form of the mineral schreibersite, (Fe,Ni)3P, is highly reactive 5,6,7. When wetted, schreibersite forms hydrous, activated phosphate capable of forming key basic organic molecules, such as glycerol phosphate, nucleosides, and phosphocholine 8,9, and intermediate phosphorus species hypophosphite (H2PO2−) and phosphite (HPO32−) 5,10. While such intermediate phosphorus species would hinder organic reactions, they may still play an important role in the origin of life by efficiently reacting with solar ultraviolet (UV) radiation and dissolved HS− to form orthophosphate (PO43−) 11” (Hess; Piazolo; Harvey 2021).
In Illinois, when the fulgurite had been dug up, researchers observed glassy bits trailing the structure’s surface, which also contained schreibersite, extending down about a foot and a half into a thick structure reminiscent of tree roots. Because phosphorus, at the onset of our world’s creation, was abundant but not in its reactive form since it was trapped in nonreactive minerals that prevented it from reacting with the organic precursors to our current genetic codes, it stands that reason that while meteors could have carried schreibersite and reactive phosphorus to Earth in the early stages of its formation (when meteor strikes were commonplace), such conditions were still too harsh for life even to have had the chance to emerge.
On the other hand, as previously discussed, lightning offers an alternative means of reactive phosphorus formation, not to mention that it, unlike meteorites, does not destroy everything within a 100-kilometer radius upon impact. This is significant because when a schreibersite is formed upon lightning’s strike, it gives phosphorus the liberty to interact with the elements comprising Earth’s primitive atmosphere. Based on the results of the Miller-Urey experiment, it is believed that this primitive atmosphere consisted of methane (CH4), ammonia (NH3), hydrogen (H2), and water (H2O). While Urey suggested these compounds comprised the paleo-atmosphere, he also suggested that Miller conduct an experiment in which a flask containing all of the above compounds underwent a constant electric spark of ~60,000 Volts for about a week. After that week, most ammonia and methane were consumed, yielding carbon monoxide (CO) and nitrogen (N2) as gaseous products. However, an accumulation of a dark substance containing an array of organic polymers was accumulated. When the researchers tested the aqueous solution, it had become evident that the electric current applied to the reactants ultimately produced “25 amino acids (the main ones being glycine, alanine, and aspartic acid),” “several fatty acids,” “hydroxy acids,” and “amide products” (Gordon-Smith 2003). A breakthrough in the controversy of life’s origin, the Miller-Urey experiment affirms that these molecules could have participated in prebiotic chemical reactions. With reduced phosphorus having become available from lightning-struck schreibersite, it may arguably be deduced that these prebiotic chemicals possibly interacted with schreibersite phosphorus to yield more complex biomolecules, but how could such interactions be facilitated?
The answer might be clay, for it would have, indeed, formed as a consequence of global temperature decreases, which may have induced volcanic glass and rock weathering. This cooldown period resulted in elevated concentrations of anions and cations precipitating to the primitive seabed, where they would have interacted with copper, gold, nickel, phosphorus, and zinc deposits. Furthermore, the oldest rocks on Earth are sedimentary by nature, providing evidence of a history of running water. Contact between water and these volcanic rocks and glass paved the way for clay mineral formation. As per the Mars investigation, “Impact craters are ubiquitous landforms in the ancient crust of Mars that expose subsurface materials and allow us to probe crustal compositions using orbitally acquired VIS-NIR reflectance spectra” (Sun, Milliken 2015), a powerful analytical method of determining optical properties of both solids and liquids. Using this method, researchers were able to deduce that the clay minerals in the Noachian southern highlands, which have been detected in higher concentrations around central peaks, crater walls, and ejecta blankets, are “generally inferred to originate from crustal depths as great as 10% of the crater diameter” (Sun, Milliken 2015). Additionally, while shallower strata in central structures can be inferred to have directly resulted from listric faulting via crater modification, the majority of central peak material, namely in upper regions, has proven it to be considered likely that, based on crater literature, its origins likely lie within the depths of these craters. Other clay mineral studies in Hesperian impact craters reveal younger clays, possibly authigenic, located in the central peaks of the craters.
“These Hesperian or Amazonian clays are proposed to have formed in a hydrothermal system, at Toro crater [Marzo et al., 2010] and an alluvial fan in Majuro crater [Mangold et al., 2012b], or in association with impact melt in the case of Ritchey crater [Sun and Milliken, 2014], suggesting that post-Noachian clay formation was possible in impact systems” (Sun, Milliken 2015).
This proves significant, for, per the hydrothermal vent model, organic molecules produced under the conditions of early Earth, akin to those produced by the Miller-Urey experiment, could have sunken to the seafloor, where hydrothermal vents generate massive seafloor sulfide (SMS) deposits rich in minerals, such as cobalt, gold, manganese, silver, and zinc. These organic vents also provide an energy source by which chemical reactions between hydrogen and carbon dioxide and sulfur-containing amino acids may yield an array of complex, organic molecules. This would explain why sulfur is the third most abundant mineral in the human body, for it is the cysteine, homocysteine, methionine, and taurine amino acids which contain sulfur, even though cysteine and methionine are the only two which are incorporated into proteins and which are used to make them. Furthermore, high temperature and pressure facilitate the adsorption of organic monomers that ultimately could have protected early biomolecules both from hydrolytic and photolytic reactions and from global glaciations, which are also proposed to have aided in the creation of life on Earth. Clay minerals may then absorb these molecules throughout the seafloor, where clay offers biomolecules protection and a structural template that both could arguably, according to Ponce and Kloprogge, have played a significant role in the development of highly concentrated systems; in the facilitation of condensation/polymerization processes; in the surface-templating for the adsorption/synthesis of organic monomers and polymers (Ponce, Kloprogge 2020).
In conclusion, while we may never know exactly how life began here on Earth, numerous findings, all of which deviate from one another, could all very well have been the catalyst for life’s emergence. Instead of focusing on who is correct, we must stick to the most feasible explanation for the development of such a complex array of organisms, from minuscule microbes to daunting dinosaurs to “civilized” civilizations. Each of the theories proposed by scientists across the globe and throughout human history has its inconsistencies, but it seems as though each theory offers a process. Which process is more feasible? Well, the human body conducts 37 thousand billion billion chemical reactions per second, most of which, if not all, are interdependent, each occurring as a result of the (in)completion of the other. Similarly, it is not unlikely that each of the theories covered in this paper may have certain truths that are dependent upon certain truths offered by other theories.
Works Cited
Greenfield, N. (2021, March 16). Lightning may have created an ingredient needed for life to
evolve. How A Building Block Of Life Got Created In A Flash.
Hashizume, H. (2012). Role of Clay Minerals in Chemical Evolution and the Origins of Life.
Clay Minerals in Nature – Their Characterization, Modification and Application. Published. https://doi.org/10.5772/50172
Hess, B.L., Piazolo, S. & Harvey, J. Lightning strikes as a major facilitator of prebiotic
phosphorus reduction on early Earth. Nat Commun 12, 1535 (2021). https://doi.org/10.1038/s41467-021-21849-2
Ponce, C. P. (2020, August 28). Urea-Assisted Synthesis and Characterization of Saponite with
Different Octahedral (Mg, Zn, Ni, Co) and Tetrahedral Metals (Al, Ga, B), a Review. MDPI. https://www.mdpi.com/2075-1729/10/9/168/htm
Sun, V. Z. (2015, December 1). Ancient and recent clay formation on Mars as revealed from a global survey of hydrous minerals in crater central peaks. AGU Journals. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2015JE004918
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