Digital ACT Reading Practice Question #1733

The primary scientific paradigm overturned by the Alvin expedition was that: Passage Excerpt (Natural Science): Until the 1977 expedition of the submersible Alvin along the Galapagos Rift, biologists believed all marine food webs were tethered to solar energy through photosynthesis. That assumption shattered 2,500 meters down, where scientists discovered basalt chimneys spewing mineral fluids at 350°C into freezing seawater. Thriving around these toxic vents were colonies of giant tube worms, blind shrimp, and crabs. Instead of sunlight, the primary energy base is chemosynthesis by lithotrophic bacteria oxidizing hydrogen sulfide from the crust to fix inorganic carbon. The six-foot tube worm Riftia pachyptila possesses no mouth or gut, relying on billions of endosymbiotic sulfur bacteria in an internal organ called the trophosome.