Question

Passage A

For decades, the standard scientific consensus regarding the origin of life on Earth pointed toward warm, sunlit surface waters. This "primordial soup" hypothesis, first popularized in the mid-twentieth century, suggested that solar radiation and atmospheric electricity sparked the creation of organic molecules in shallow lagoons. However, the discovery of hydrothermal vents along the Galápagos Rift in 1977 radically upended this paradigm. Operating in complete darkness under crushing pressures, these deep-sea ecosystems thrived entirely independent of sunlight, powered instead by chemosynthesis—the synthesis of organic compounds using energy derived from inorganic chemical reactions.

This revelation led many geobiologists to propose that the hydrothermal environments of the deep ocean floor, rather than shallow surface ponds, were the true crucibles of terrestrial life. Early research focused primarily on "black smokers"—steep, chimney-like mineral structures formed where superheated, highly acidic water (exceeding 350°C) saturated with metal sulfides erupts from beneath the ocean crust into the freezing sea. Proponents of the deep-sea origin theory argue that the extreme temperature gradients and rich mineral mixtures found at these sites provided the necessary thermal energy and chemical catalysts to assemble the first complex organic polymers. Moreover, the sheer volume of water circulating through the ocean crust suggests that these vents were widespread on the early Earth, offering a vast number of molecular laboratories.

Yet, critics of the black smoker hypothesis point out significant thermodynamic hurdles. The extreme temperatures that define these volcanic vents are highly destructive to fragile organic compounds like amino acids and nucleic acids, which decompose rapidly when heated. Additionally, the high acidity of the fluids inhibits the stable formation of cell-like membranes. While black smokers demonstrated that complex ecosystems could flourish without photosynthesis, many researchers remained skeptical that the earliest, most delicate precursor molecules of life could have survived their volatile environments long enough to organize into self-replicating entities.

Passage B

The debate over the origin of life shifted dramatically in 2000 with the discovery of the "Lost City" hydrothermal field near the Mid-Atlantic Ridge. Unlike the basalt-hosted black smokers, Lost City is an alkaline hydrothermal system fueled by serpentinization—a chemical reaction between seawater and mantle rocks. The fluid venting from these carbonate chimneys is cool (40°C to 90°C), highly alkaline (pH 9 to 11), and rich in dissolved hydrogen and methane. For many molecular biologists, this discovery resolved the thermal and chemical challenges that plagued the earlier black smoker models of life's origin.

Alkaline vents offer a far more hospitable cradle for primordial chemistry. The moderate temperatures preserve organic molecules rather than destroying them, and the porous carbonate structures function as natural inorganic cells. The microscopic cavities within these mineral chimneys could concentrate organic molecules, providing a physical compartment where metabolism could develop before the evolution of lipid cell membranes. Crucially, the interface between the alkaline vent fluids and the acidic ancient ocean created a natural proton gradient, mimicking the electrical charge across modern cell membranes that drives ATP synthesis. This geochemical engine suggests that life is not a freak accident of surface chemistry, but a predictable consequence of planetary cooling and water-rock interactions that occurred globally in the early oceans.

Despite their differences in chemical mechanism, both the black smoker and alkaline vent models share a fundamental premise: they relocate the cradle of life from the Earth's surface to the dark abyss of the ocean floor. By demonstrating that geochemical energy can drive the synthesis of organic precursors, both theories challenge the classic notion that life required solar radiation to begin. While the scientific community continues to debate the precise pathway from geochemistry to biochemistry, the consensus has increasingly shifted away from the sunlit surface, recognizing that the deep ocean provided the stable, energy-rich sanctuary necessary for the spark of life.

Based on the passages, which passage or passages support each of the given claims?