The following passage is adapted from an essay on the history of astrobiology and subsurface ecology:
For decades, biology textbooks defined the biosphere as a thin, sunlit envelope clinging to Earth's surface, where photosynthesis fueled virtually all ecological chains. This surface-centric view began to fracture in the late twentieth century with the discovery of microbes living miles beneath the seafloor and deep within continental basalt. These subsurface organisms, collectively termed the 'deep biosphere,' operate in complete darkness under crushing pressures, drawing energy not from sunlight but from chemolithoautotrophy—the chemical weathering of rocks and radioactive decay. While initial discoveries were dismissed as surface contamination, subsequent sterile drilling initiatives confirmed that these deep-dwelling prokaryotes constitute a massive fraction of Earth's total biomass. However, the significance of the deep biosphere extends beyond mere numbers or exotic metabolic pathways. It challenges our understanding of the conditions necessary for life, suggesting that planetary habitability is not solely determined by stellar proximity or surface water. Instead, the interior of a planet, long considered inert, may serve as a primary incubator of life, rendering geothermal activity far more critical than solar radiation in astrobiological models. Consequently, the search for extraterrestrial life has shifted from a preoccupation with surface liquid water to the investigation of sub-surface heat and chemistry.
Which statement best summarizes the author's primary argument in the passage as a whole?
- AMicrobes in the deep biosphere survive in dark, high-pressure environments by utilizing chemolithoautotrophy, which involves extracting energy from chemical weathering and radioactive decay.
- BSubsurface microbial life constitutes the majority of Earth's biomass and demonstrates that geothermal energy is the sole source of ecological productivity on planetary bodies.
- The discovery of the deep biosphere has fundamentally revised scientific conceptions of planetary habitability, shifting the search for extraterrestrial life from surface environments to subsurface geothermal systems.Answer
- DInitial scientific skepticism regarding the deep biosphere arose because sterile drilling methods were unable to prevent contamination from surface organisms.