Chapter 1: The Foundations of Life

The concept of evolution, famously articulated by Charles Darwin, provides a comprehensive narrative on how life evolved from simple, single-celled organisms into the diverse array of mammals we see today. However, the fundamental question remains: what initiated life itself? How did life emerge from inanimate matter? What underpins the process of evolution? For many years, researchers across physics, chemistry, and biology have delved into the phenomenon of abiogenesis — the natural emergence of life from non-living components.

At the core of this narrative are atoms, the fundamental units of matter. The elements carbon, hydrogen, oxygen, phosphorus, sulfur, and nitrogen serve as the essential building blocks for all terrestrial life. Under the specific conditions present on Earth's surface, these elements exhibit unique interactions. Among the 98 elements found on our planet, these six form a closely-knit 'family' that may not combine in the same way elsewhere in the universe. Imagine these elements as parts of a colossal divine assembly kit, capable of generating countless intricate structures. These atoms, plentiful in the primordial oceans of the early Earth, set the stage for the emergence of life.

The constant quest for a lower energy state drives the formation of new combinations of these six elements. When two chemical entities react to form a new product, the energy balance shifts. If the product’s internal energy exceeds that of the reactants, energy input is necessary. Conversely, if the product's energy is lower, a certain amount of activation energy is still required to initiate the reaction. To illustrate, consider the spark needed to ignite a fire, where carbon and oxygen combine to produce carbon dioxide and release energy in the form of heat and light.

This principle applies broadly. For instance, plants harness ultraviolet radiation to convert carbon dioxide back into oxygen and carbon. This transformation requires a specific environment to optimize the energy provided by UV light, which could otherwise lead to constant oxygen production from carbon dioxide in our atmosphere. A simpler analogy might be dropping a rock into a ravine: the rock falls due to the gravitational pull toward a lower energy state.

In 1953, Stanley Miller and Harold Urey conducted groundbreaking experiments demonstrating that life’s building blocks could form under conditions resembling those of early Earth. They proposed that the primordial atmosphere consisted of ammonia, carbon monoxide, hydrogen, methane, and water vapor. By subjecting this gas mixture to high-voltage electrical discharges, they simulated the violent storms believed to have occurred in Earth's infancy. Collecting the resulting rainwater, they discovered amino acids formed spontaneously, providing the first tangible evidence that life could originate from non-living materials.

In this primordial ocean, molecules such as alcohols, simple sugars, carbonic acids, amino acids, and nucleic bases likely emerged, paving the way for life. These molecules could link together to form larger, complex compounds: sugars could form chains (polysaccharides), and amino acids could combine to create polypeptides, which are precursors to the proteins that perform vital functions in our bodies.

Though many compounds were unstable and prone to change, some proved resilient, breaking down only under significant energy input. This random combination process leading to more intricate and stable compounds is known as chemical evolution. It unfolded gradually during Earth's formative years, serving as a prelude to the vibrant tapestry of life that would follow.

Life relies on complex and stable chemical compounds, essential for self-organization and replication. Thus, it requires stable building blocks that can form molecular chains of varying lengths. These chains must be relatively inert, resisting reactions with other environmental molecules. Nucleic bases serve as ideal building blocks, with five key members: uracil, thymine, cytosine, adenine, and guanine. The first three are derived from pyrimidine, a stable hexagonal structure likely formed under early Earth conditions.

Nucleic bases can bond with ribose (a sugar formed in the primordial oceans) and phosphate to create nucleoside monophosphates (NMPs). This process probably occurred on the mineral surfaces of underwater volcanoes, the hotspots of abiogenesis where the fundamental building blocks of life were forged. If volcanic eruptions released pyrophosphates, NMPs could combine with them to form nucleoside triphosphates (NTPs), compounds that require less energy to release their internal energy.

These NTPs are vital in modern organisms; for instance, adenosine triphosphate (ATP) acts as a crucial energy store for cellular metabolism. NTPs can also link together, releasing pyrophosphate, resulting in lengthy chains of nucleic bases — ultimately forming ribonucleic acid (RNA).

As RNA molecules formed, they often fused or were split apart by electromagnetic radiation or reactive molecules. This cleavage followed the rules of energy optimization: when a high-energy photon strikes RNA with sufficient energy, it can optimally cleave the molecule. Similarly, reactive radicals can lead to new compounds through energetic interactions.

Pyrimidine, a stable compound, has been found in many meteorites, suggesting its cosmic origins from the remnants of dying stars. In Earth's early history, meteorites may have delivered this creative stardust, contributing to the formation of life's building blocks. Notably, NASA reported in March 2015 that pyrimidine, along with other primitive components, could independently form nucleic bases in the cold of space, mimicking conditions thought to exist on early Earth.

We are all made of stardust | George Coyne | TEDxYYC - YouTube

Explore the connection between stardust and the essence of life, as George Coyne discusses how the universe's elements contribute to our existence.

Chapter 2: The Cosmic Connection

We're All Stardust: A Once-in-a-PhD Supernova - YouTube

Join a deep dive into how supernovae create the elements that form life, reinforcing our connection to the universe.