Unit D – Plate Tectonics
1. Active – A volcano that is currently erupting, showing signs that it is likely to erupt in the near future, or
has erupted in recorded history.
2. Dormant – A volcano that has not erupted for at least 10,000 years, but that scientists think may erupt
again.
3. Extinct – A volcano that scientists do not expect to erupt ever again.
4. Nuclear Waste – Radioactive material that must be disposed because it is not useful.
5. Magma – Molten rock found beneath the earth’s surface.
6. Core – The innermost area of the earth’s interior.
7. Crust – The thin outermost “layer” of the earth.
8. Lava – Molten rock found on top of the earth’s surface.
9. Lithosphere – The rigid upper portion of the earth that is broken into plates. It includes the crust and the
uppermost portion of the mantle.
10. Asthenosphere – The plastic-like layer below the lithosphere.
11. Mantle – The “layer” of the earth between the outer crust and inner core.
12. Cinder Cone – A volcano formed from explosive eruptions that shoot small pieces of magma and ash
into the air.
13. Composite Volcano – A volcano that has explosive eruptions as a result of more gassy magma.
14. Shield Volcano – A volcano that releases relatively fast-moving, less gassy lava, and have less explosive
eruptions.
15. Cross-section – A slice of an object made by cutting through it in a plane at right angles to an axis.
16. Crater – The steep-walled depression around a volcano’s vent.
17. Volcanologist – A scientist who studies volcanoes and volcanic phenomena.
18. Paleontologist – A scientist who uses fossil evidence to study life in prehistoric times.
19. Reptile – Any of various cold-blooded animals, such as snakes, turtles, and crocodiles, that have a
backbone.
20. Continent – One of the seven great landmasses of the earth, including Africa, Antarctica, Asia, Australia,
Europe, North America, and South America.
21. 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.
22. Theory – A logically consistent explanation of some aspect of the natural world that is supported by a
large body of evidence.
23. Continental Drift – A theory that the continents were attached together in the past, and have been drifting
apart ever since.
24. Plates – Large sections of the earth’s surface.
25. 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.
26. Seafloor Spreading – Harry Hess’s theory that new seafloor is formed when magma is forced upward
toward the surface at a mid-ocean ridge.
27. Convection Current – A flow of material (such as magma in the earth’s mantle) caused by a temperature
difference.
28. Convergent – A boundary between tectonic plates that are moving toward each other.
29. Divergent – A boundary between tectonic plates that are moving away from each other.
30. Transform – A boundary between tectonic plates that are sliding next to each other.
31. Earthquake – The release of energy in the form of waves that occurs when large masses of rock below
earth’s surface suddenly shift position.
32. Fault – A crack in a rock mass along which there has been movement caused by the shifting of the
earth’s crust.
33. Focus – In an earthquake, the point below Earth’s surface where energy is released in the form of seismic
waves.
34. Epicenter – The point on Earth’s surface directly above the earthquake focus.
35. Richter Scale – A scale used to quantitatively rate the magnitude of an earthquake.
36. Hot Spot – A place on earth’s surface that is directly above a column of rising magma called a mantle
plume.
37. Seismogram – The information recorded by a seismograph.
38. Seismograph – An instrument that measures and records the intensity of an earthquake.
39. Subduction – An area where one tectonic plate is being forced downward toward the earth’s interior.
40. Risk – The chance that a particular action or event could result in something unfavorable, such as injury
or death.