Unit D Vocabulary
1. convection current A flow of material (such as magma in the earth’s mantle) caused by a temperature difference.
2. convergent boundary A boundary between tectonic plates that are moving toward each other.
3. core The innermost area of earth’s interior.
4. crust The thin outermost “layer” of the earth. See also core, mantle, and lithosphere.
5. continental drift A theory that the continents were attached together in the past, and have been drifting apart ever
since.
6. divergent boundary A boundary between tectonic plates that are moving away from each other. Also called a
spreading center.
7. dormant (volcano) A volcano that has not erupted for at least 10,000 years, but that scientists think may erupt
again.
8. geological time Periods of thousands, millions, and billions of years referred to by geologists, paleontologists, and
other scientists who study the earth’s history.
9. lava Molten rock found on top of the earth’s surface
10. lithosphere The rigid upper portion of the earth that is broken into plates. It includes the crust and the uppermost
portion of the mantle.
11. magma Molten rock found beneath the earth’s surface.
12. mantle The “layer” of the earth between the outer crust and inner core.
13. paleontologist A scientist who uses fossil evidence to study life in prehistoric times.
14. Pangea or Pangaea A single landmass, or supercontinent, that existed from about 350 million to 200 million years
ago and was separated by plate tectonics, forming the current continents.
15. plate boundary Where the edges of two (or more) tectonic plates meet. See plates, plate tectonics.
16. plate tectonics The theory that the rigid outer portion of the earth is broken into large separate sections, called tectonic
plates, each moving at a specific speed in a specific direction. The movement of tectonic plates helps explains
the occurrence of earthquakes, volcanoes, and many other geologic phenomena.
17. Richter scale A scale used to quantitatively rate the magnitude of an earthquake. Each increase of 1 on the Richter
scale is equal to a 30-fold increase in released energy.
18. seismograph An instrument that measures and records the intensity of an earthquake.
19. subduction zone An area where one tectonic plate is being forced downward toward the earth’s interior. This process
causes the solid portions of the subducted plate to melt.
20. tectonic plate A large section of the rigid outer portion of the earth that is moving at a specific speed in a specific
direction.
21. transform boundary A boundary between tectonic plates that are sliding next to each other. also called a strike-slip
boundary.
22. tsunami a large wave that forms when an earthquake, volcano, landslide, or other event moves a very large amount of
water uncontrolled variable A variable in an experiment or investigation that the experimenter either
ignores or is unable to hold constant.
23. volcano A landform, often conical, made from igneous rocks that form when magma from below the earth’s surface
erupts on to the surface.