Geologic Time

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Across
  1. 2. the formation of new areas of oceanic crust, which occurs through the upwelling of magma at midocean ridges and its subsequent outward movement on either side.
  2. 4. the relatively thin part of the earth's crust which underlies the ocean basins. It is geologically young compared with the continental crust and consists of basaltic rock overlain by sediments.
  3. 6. a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.
  4. 7. a type of excavation or depression in the ground that is generally deeper than it is wide (as opposed to a wider gully, or ditch), and narrow compared with its length (as opposed to a simple hole or pit).
  5. 8. a massive, irregularly shaped slab of solid rock, generally composed of both continental and oceanic lithosphere.
  6. 11. the layer of igneous, sedimentary, and metamorphic rocks that forms the geological continents and the areas of shallow seabed close to their shores, known as continental shelves.
  7. 12. in early geologic time, a supercontinent that incorporated almost all the landmasses on Earth.
  8. 13. an elevated region with a central valley on an ocean floor at the boundary between two diverging tectonic plates where new crust forms from upwelling magma.
  9. 15. an elevated portion of the Earth's crust, generally with steep sides that show significant exposed bedrock.
  10. 16. the block above the fault moves up relative to the block below the fault.
  11. 18. a theory that explained how continents shift position on Earth's surface.
  12. 19. magma once it has been expelled from the interior of a terrestrial planet or a moon onto its surface.
  13. 20. the movement caused within a fluid by the tendency of hotter and therefore less dense material to rise, and colder, denser material to sink under the influence of gravity, which consequently results in transfer of heat.
  14. 21. the molten or semi-molten natural material from which all igneous rocks are formed.
Down
  1. 1. a fault on which the two blocks slide past one another.
  2. 3. when two tectonic plates move away from each other.
  3. 5. an area on Earth where two or more lithospheric plates collide.
  4. 9. a path along the Pacific Ocean characterized by active volcanoes and frequent earthquakes.
  5. 10. places where plates slide sideways past each other.
  6. 14. a sudden and violent shaking of the ground, sometimes causing great destruction, as a result of movements within the earth's crust or volcanic action.
  7. 17. volcanic locales thought to be fed by underlying mantle that is anomalously hot compared with the surrounding mantle.