Plate Tectonics

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Across
  1. 2. The thick layer of rock between the Earth's crust and its core, making up roughly eighty-four percent of the planet's volume — solid enough to transmit seismic waves but capable of very slow plastic flow over geological time, making it the medium through which the planet's internal heat is transferred and through which the tectonic plates move.
  2. 4. The scientific study of ancient life through the analysis of fossils — a discipline that contributed crucial evidence for continental drift by documenting the presence of identical ancient species on continents now separated by vast oceans.
  3. 8. A dark, dense volcanic rock that forms the foundation of the ocean floor and the oceanic tectonic plates — denser than the granite-rich continental crust, which is why oceanic plates sink beneath continental ones at subduction zones rather than riding over them.
  4. 9. Relating to the large-scale structure of the Earth's outermost layers and the forces that build, deform, and reshape them — a word originally borrowed from architecture, where it described the craft of building, and applied to the Earth to describe the planet's own grand construction project.
  5. 10. The rigid outer shell of the Earth — comprising the crust and the uppermost solid part of the mantle — that is broken into the moving tectonic plates, as distinct from the more ductile, slowly-flowing layer below it.
  6. 11. The pattern of how often a particular type of event happens in a given location over time — used in seismology to describe the average interval between large earthquakes on a specific fault, which informs probabilistic hazard assessments for regions at risk.
  7. 15. The branch of geology that studies rock layers — their sequence, composition, and the environments in which they were deposited — which allows scientists to reconstruct the history of a region and to correlate rock formations on continents now separated by oceans, as Wegener did in building his case for continental drift.
  8. 17. Moving toward each other and meeting — used to describe the type of tectonic boundary where plates are colliding, with consequences that depend on whether the plates are both continental, both oceanic, or one of each.
  9. 19. Having the thick, slow-flowing quality of a substance that resists movement and deformation — like honey or syrup — used in the article to describe how the Earth's mantle behaves over geological timescales, moving despite being technically solid.
  10. 20. A vast landmass formed by the joining of multiple continental plates into a single connected whole — the planet has produced several of these over its history, each of which eventually broke apart under the same tectonic forces that had assembled it.
Down
  1. 1. A measure of the total energy released by an earthquake, expressed on a logarithmic scale in which each whole-number increase represents roughly thirty times more energy — meaning the difference between a small and a large earthquake is far greater than the numbers alone suggest.
  2. 3. The point on the Earth's surface located directly above the underground point where an earthquake rupture begins — typically the location of most intense ground shaking, though local geological conditions can significantly modify how the energy is felt at the surface.
  3. 5. The transfer of heat through the movement of a fluid, in which hot, less dense material rises while cooler, denser material sinks, creating a circular current — the process driving movement in Earth's mantle, in the atmosphere, and in the oceans.
  4. 6. The branch of science devoted to studying earthquakes and the seismic waves they generate — using those waves not only to understand earthquakes themselves but also to peer inside the Earth's interior, since different wave types travel at different speeds through different materials.
  5. 7. The geological process by which one tectonic plate is forced beneath another plate and drawn down into the mantle, creating deep ocean trenches, volcanic arcs, and the conditions for the largest earthquakes ever recorded.
  6. 12. Changing direction or character — used to describe the type of tectonic boundary where plates slide horizontally past each other without creating or destroying crust, a motion that generates enormous friction, stress accumulation, and significant earthquake hazard.
  7. 13. Moving apart from each other — used to describe the type of tectonic boundary where plates are separating, allowing new crust to form in the gap as magma rises from below, and producing ocean ridges on the seafloor or rift valleys on land.
  8. 14. The name given by a pioneering German scientist to the ancient supercontinent he proposed had once contained all of Earth's present-day landmasses, before breaking apart over hundreds of millions of years to produce the configuration of continents we see today.
  9. 16. The point underground where the rupture that causes an earthquake actually initiates — also called the focus — from which the seismic waves radiate outward in all directions through the surrounding rock.
  10. 18. A long, narrow fracture or break in the Earth's crust where tectonic forces are pulling the land apart — on land, these form elongated valleys flanked by elevated shoulders; in the ocean, they become mid-ocean ridges as new crust fills the widening gap.