Chapter 1: Myths and Theories of Creation

Creation myths are prevalent across various cultures. For instance, the African Bushmen held the belief that humans and animals initially lived underground in a utopian environment. According to their lore, a deity led them to the surface, instructing them not to kindle fires. However, when night fell and the cold set in, they disobeyed and lit fires. Such narratives often overlook the origins of life itself, as characters seem to exist without explanation. Other religious texts, like the Bible, present God as the creator of life.

These myths were not meant to serve as scientific explanations but rather to define humanity's relationship with creation and reflect on existential questions. However, billions of years before humans appeared, fossil and geological evidence shows that no human experience existed.

The release of Charles Darwin's "On the Origin of Species" marked a pivotal shift in our comprehension of life and its complexities, suggesting that such intricacies could arise without divine involvement. Though the initial theory contained errors, it was refined to connect with the chemistry underpinning life as we know it today.

Darwin postulated in his seminal 1859 work that all species descended from common ancestors, and he hypothesized that "all the organic beings which have ever lived on this earth have descended from some one primordial form." However, the conditions that facilitated the emergence of life remained poorly understood. Questions arose: Why does life not spontaneously arise at all times? Why did it occur only billions of years ago? Early Earth must have had specific conditions that allowed for life, such as a lack of oxygen-producing organisms.

In 1924, Russian biochemist Alexander Oparin suggested that life began in a dense, warm "soup" teeming with organic molecules, as articulated in his influential book, "The Origin of Life." This primordial soup may have been edible to primitive life forms when heated. Organic compounds generated in the atmosphere from lightning, solar wind, UV radiation, and meteorite impacts would have fallen into the early oceans. Hydrothermal vents, hot springs, and volcanoes likely provided the necessary heat to catalyze the development of life.

Oparin speculated that life emerged spontaneously from this primordial concoction. Following his publication, prominent scientists such as J.B.S. Haldane, J.D. Bernal, Melvin Calvin, and Harold Urey contributed to expanding this concept.

In 1953, Stanley Miller, along with Urey, conducted a groundbreaking experiment where they combined water, hydrogen, methane, and ammonia gases in a sealed apparatus. By introducing steam to mimic early atmospheric conditions and simulating lightning with electrical sparks, they demonstrated how the early atmosphere could yield amino acids from simple chemical reactions. This experiment laid the foundation for the field of experimental prebiotic chemistry, which investigates the emergence of life from non-living materials.

Chapter 2: The RNA World Hypothesis

In 1962, Alexander Rich introduced the RNA world hypothesis, proposing that strands of RNA served as the original replicators that enabled natural selection to occur. RNA, a simpler cousin of DNA, is capable of storing genetic information. In this model, RNA not only stored genetic data but also facilitated chemical reactions in primordial cells, later transitioning to more stable DNA forms.

Despite the RNA world hypothesis having substantial supporting evidence, it does not elucidate how life initially began. The strong version of this theory posits that RNA formed spontaneously to become the sole replicator on early Earth—a notion that seems improbable given its complexity. Moreover, modern cellular structures suggest older origins than RNA, as enzymes like metalloproteins contain iron-sulphur clusters that may predate RNA.

Additionally, the primordial soup concept raises questions about its formation amidst vast oceans of water. An alternative theory suggests that life originated from carbon dioxide interacting with mineral pyrite on the surface. As pyrite oxidized into iron monosulphide and hydrogen sulfide, metabolic processes could have commenced. However, this theory faces similar challenges as the soup concept, particularly regarding the conditions necessary for replication to occur.

A further challenge in understanding life's origins resembles the classic chicken-and-egg dilemma: Which came first, metabolism or replication? Utilizing energy from nutrients requires metabolic processes, which cannot occur without chemical reactions in cellular components. For instance, in human cells, mitochondria generate ATP as the energy currency.

Mitochondria are believed to have evolved from free-living prokaryotes that formed a symbiotic relationship with early cells. These prokaryotes share many characteristics with mitochondria today, suggesting a long evolutionary connection.

The transition from organic mixtures to cellular membranes also presents difficulties. Membranes are complex structures that protect and organize metabolic and replication components, and they must have existed before natural selection favored their evolutionary advantages.

The resolution to these challenges may lie in the hypothesis that life originated around 3.8 billion years ago in small compartments at the ocean's depths. These compartments, often less than a millimeter in size, could have contained iron-monosulphide as a catalyst while hydrothermal vents provided the essential energy. These small pockets would have prevented organic compounds from diffusing into the ocean, allowing them to concentrate and facilitate the emergence of life.

Chemical reactions within these hydrothermal environments would have sustained life, kickstarting metabolic processes. A critical component of metabolism across all life forms is acetyl-CoA (acetyl coenzyme A). This molecule plays a key role in the Krebs Cycle, which metabolizes carbohydrates.

The acetyl-CoA pathway is believed to be one of the most ancient biochemical processes due to its simplicity. Remarkably, metal-sulfides can convert carbon dioxide into acetyl-CoA without requiring ATP or mitochondria, indicating that iron-monosulfide found in hydrothermal compartments may have been a precursor to mitochondria.

This suggests that inorganic metabolic processes could have emerged before the evolution of replicating components like RNA, implying that the "chicken feed" preceded the "egg." As organic materials were metabolized, the likelihood of RNA formation increased, particularly in cooler regions of the vents, where convection currents facilitated concentration.

Moreover, these vents were alkaline, while oceans were acidic, creating a proton gradient—positively charged outside and negatively charged inside. This proton gradient is crucial in modern biological membranes, as cells harness it to generate energy.

The proton gradient operates similarly to a hydroelectric dam. As nutrients are metabolized, they pump protons across the membrane, creating a reservoir of protons on one side. The flow of protons through embedded proteins catalyzes ATP synthesis, a process for which Peter Boyer and John Walker received the Nobel Prize in 1997.

This discovery revealed that cellular metabolism deviates from standard chemical processes, relying instead on a mechanism known as chemiosmosis. Proposed by Peter Mitchell in 1961, this concept initially faced skepticism but eventually gained acceptance.

Yet, questions persist regarding why life utilizes three-dimensional cell membrane chemistry. Traditional chemistry often overlooks spatial dimensions, yet proton gradients demand a spatial framework. The universal ancestor of all life must have possessed a proton gradient to facilitate its proliferation beyond hydrothermal vents.

The relationship between proton gradients in cells and those in hydrothermal vents has not been thoroughly explored in research literature, yet it appears vital to understanding how life arose before the advent of cell membranes. Inorganic structures within these vents may have served similar functions.

This perspective challenges the soup theory, which implies equilibrium and lacks the energy inflow necessary for life to emerge. While lightning and UV radiation can generate organic compounds, they cannot spontaneously produce life.

Instead, it seems plausible that life arose in the pores of hydrothermal vents, where iron-monosulfides, carbon dioxide, and amino acids coexisted, driven by the proton gradient between the alkaline vent and acidic ocean, ultimately leading to the first single-celled organisms.

These organisms may have thrived through chemical processes within the vents, relying on a steady supply of sulfides. However, to survive outside this environment, they would need their own proton gradients.

This necessity is not merely a byproduct of evolution but a fundamental requirement for generating sufficient ATP for growth and replication. Traditional chemical reactions yield only one ATP per reaction, whereas chemiosmosis allows for more efficient energy conversion, enabling life to thrive.

Ultimately, the emergence of life may resemble a primordial hive, where clusters of living matter, protected by inorganic structures, initiated replication and established an engine for growth. While this theory does not resolve every aspect of life's origins, it suggests that inorganic processes may have been foundational to the development of early cell membranes and mitochondria, preceding the biological functions we associate with life today.

References

Lane, Nick, John F. Allen, and William Martin. "How did LUCA make a living? Chemiosmosis in the origin of life." BioEssays 32.4 (2010): 271–280.

Wächtershäuser, Günter. "Pyrite formation, the first energy source for life: a hypothesis." Systematic and Applied Microbiology 10.3 (1988): 207–210.

Russell, Michael J., John F. Allen, and E. James Milner-White. "Inorganic complexes enabled the onset of life and oxygenic photosynthesis." Photosynthesis. Energy from the Sun: 14th International Congress on Photosynthesis. Springer Netherlands, 2008.

Russell, Michael J., and William Martin. "The rocky roots of the acetyl-CoA pathway." Trends in biochemical sciences 29.7 (2004): 358–363.