Passage
In 1912, German meteorologist Alfred Wegener proposed a radical hypothesis that challenged the geological orthodoxy of his day: continental drift. Wegener argued that Earth's continents were not static, anchored fixtures, but had once been joined in a single supercontinent he named Pangaea. Over millions of years, he suggested, this massive landmass broke apart, and the fragments drifted to their present positions. To support his claim, Wegener compiled an impressive array of empirical evidence, noting the jigsaw-like fit of the coastlines of South America and Africa, matching fossil remains of the ancient reptile *Mesosaurus* across now-distant oceans, and identical geological strata on separate continents. Despite this evidence, the scientific community largely rejected Wegener's ideas. The fatal flaw of continental drift was its lack of a plausible mechanism. Wegener proposed that the continents plowed through the solid ocean floor, driven by tidal forces and Earth's rotation—forces that physicists quickly demonstrated were mathematically insufficient to move landmasses.
For decades, geology remained anchored to the belief in a rigid, unchanging Earth. However, the mid-twentieth century brought technological innovations that would reopen Wegener's cold case. During World War II and the postwar years, military sonar technology allowed researchers to systematically map the ocean floor for the first time. Far from being a flat, featureless abyss, the deep ocean was revealed to contain massive, winding mountain ranges, the most prominent being the Mid-Atlantic Ridge. Scientists also discovered deep rift valleys running down the center of these ridges, alongside unexpectedly thin sediment layers near the ridges and much thicker layers further away. These bathymetric discoveries suggested that the ocean basin was far more geologically active than previously assumed, sparking intense debate about the processes shaping the seabed.
In the early 1960s, geologist Harry Hess synthesized these new observations into a groundbreaking concept: seafloor spreading. Hess hypothesized that the mid-ocean ridges were zones where Earth’s mantle was upwelling. As magma rose to the surface at these ridges, it cooled and hardened to form new oceanic crust. This newly created crust was then continually pushed outward, away from the ridge, as fresh magma emerged behind it. Crucially, Hess proposed that the ocean floor acted as a conveyor belt, carrying the continents along with it, rather than the continents plowing through the sea floor as Wegener had imagined. This elegant hypothesis solved Wegener’s mechanism problem: continents moved not because they were drifting independently, but because they were riding on top of a dynamic ocean floor that was constantly renewing itself.
While Hess’s concept was theoretically appealing, it required concrete empirical proof. This came in 1963 through the work of geophysicists Fred Vine and Drummond Matthews, who analyzed magnetic surveys of the seafloor. They knew that Earth's magnetic field periodically reverses its polarity. As basaltic magma cools at mid-ocean ridges, iron-bearing minerals align themselves with the prevailing magnetic field, locking in a record of the polarity at that moment. Vine and Matthews discovered a symmetrical pattern of alternating magnetic stripes on either side of the mid-ocean ridges. These stripes mirrored each other precisely, recording periods of normal and reversed polarity. This paleomagnetic evidence provided the definitive tape recording of seafloor spreading, proving that new crust was indeed being created at the ridges and moving outward over time.
By the late 1960s, these disparate discoveries were synthesized into the unified theory of plate tectonics. This modern paradigm views Earth’s lithosphere not as a single solid shell, but as a mosaic of rigid plates that float on the semi-fluid asthenosphere beneath. The interactions at plate boundaries—divergent, convergent, and transform—explain not only the drifting of continents and seafloor spreading, but also the distribution of earthquakes, volcanoes, and mountain belts. Through a progression from Wegener’s initial observations to technological exploration and magnetic validation, geology underwent a profound revolution, shifting from a view of a static planet to one of a highly dynamic and interconnected system.
Which of the following options best describes the overall organizational pattern of the passage?
- AA cause-and-effect analysis that attributes Wegener’s failure to mathematical errors, followed by a study of how military sonar technology directly forced geophysicists to accept plate tectonics.
- BA comparison-and-contrast structure that weighs the merits of Wegener's continental drift against Hess’s seafloor spreading, detailing why modern geologists still debate both theories.
- A chronological account of a scientific theory's evolution, moving from an early rejected hypothesis, through mid-century technological discoveries and mechanism proposals, to empirical validation and eventual unification.Answer
- DA problem-solution framework that introduces the danger of volcanic activity along plate boundaries, proposes technological sonar mapping as a solution, and lists the steps taken to prevent earthquakes.