The Genesis of Life on Earth

Fossilized microorganisms suggest life's emergence as early as 4–4.2 billion years ago, sparking the age-old question: How did life begin? The idea of life originating from nonliving matter, known as spontaneous generation, traces back to ancient Greece but was challenged by Louis Pasteur's experiments in 1859. In the mid-1920s, spontaneous generation resurfaced, now called abiogenesis. Russian biochemist Alexander Oparin and British evolutionary biologist J.B.S. Haldane, independently, proposed that Earth's primordial conditions differed significantly from today, fostering chemical reactions forming organic molecules from inorganic compounds. While numerous theories about life's origin exist, most are grounded in the Oparin-Haldane hypothesis.

Abiogenesis, or biopoiesis, unfolds in several stages: Small organic molecules like amino acids and nitrogen-containing bases arise from atmospheric carbon dioxide and nitrogen, energized by intense sunlight or UV radiation. These molecules combine to form macromolecules, such as proteins and nucleic acids. These macromolecules aggregate within protocells, precursors to living cells enclosed by membranes regulating internal chemistry. Under these conditions, reproduction, energy production, and chemical reactions occur. In the final stage, self-replicating ribonucleic acid (RNA) emerges, essential for protein synthesis and capable of performing enzyme functions vital for RNA replication. The distinctive chemistry of these RNA molecules enhances self-replication, enabling them to pass favorable traits to descendant RNA molecules—an early example of natural selection.

For millennia, the origin of life on Earth has been a profound inquiry, vexing scholars and philosophers alike. Roughly one billion years after the Earth's formation, its conditions were markedly distinct and favorable for the emergence of basic organic compounds from the elemental components in the early atmosphere.