What evidence supports plate tectonics and how are earthquakes and volcanoes related?

• A. Evidence is limited to fossil distribution; plate tectonics is not necessary to explain earthquakes.
• B. Paleomagnetism, seafloor spreading, and the distribution of earthquakes and volcanoes; plate boundaries cause earthquakes and volcanism, with subduction zones producing deep earthquakes and magmatic activity.
• C. Earthquakes occur randomly and are not linked to plate boundaries.
• D. Volcanoes are caused by meteor impacts rather than tectonic activity.

Answer: (B)

The key idea being tested is how multiple lines of evidence converge to support plate tectonics and how the movement of plates explains both earthquakes and volcanoes. Paleomagnetism shows ancient rock magnetization that records past plate motions and reversals, revealing that continents and ocean floors have wandered over time. Seafloor spreading reveals new oceanic crust forming at mid-ocean ridges and then moving outward, which creates symmetric magnetic stripes on either side of ridges and a pattern of younger crust at the ridges. When you look at the world map of earthquakes and volcanoes, they cluster along plate boundaries, not randomly in the middle of plates, and subduction zones in particular host deep earthquakes and volcanic activity due to the melting of the subducting slab and nearby mantle.

This combination of evidence—paleomagnetic records, the creation and movement of new seafloor, and the consistent arrangement of earthquakes and volcanoes along boundaries—provides a coherent picture that plate tectonics explains the seismic and volcanic activity we observe. Plate boundaries are where rocks interact and stress builds up, releasing as earthquakes, and where melting occurs to fuel volcanism. Divergent boundaries tend to have shallow earthquakes and volcanic activity at mid-ocean ridges, while convergent boundaries (especially subduction zones) produce deep earthquakes and strong magmatic volcanism. Transform boundaries produce earthquakes along faults with little accompanying volcanism, illustrating how different boundary interactions map onto the observed patterns.