| A | B |
|---|
| outer core | it is liquid, about 1,700 km thick and separated fromn the inner solid core by a tansition zone about 565 km thick |
| pangaea | a supercontinent that existed from about 300 to 200 million years ago, and included most of the continental crust of the Earth |
| plate | a rigid segment of the Earth's lithosphere that moves horizontally and adjoins other plates along zones of seismic activity. Plates may include portions of both continents and ocean basins |
| plate boundaries | the zones of seismic activity along which plates are in contact. These may coincide with continental margins, but usually do not. Movement between plates is predominately horizontal, and may be divergent, or convergent, or side-by-side |
| plate tectonics | a theory of global tectonics according to which the lithosphere is divided into mobile plates. The entire lithosphere is in motion, not simply those segments composed of continental material |
| seismograph | an instrument that detects, magnifies, and records vibrations of the Earth, especially earthquakes |
| sill | a tabular igneous intrusion that parallels the planar structure of the surrounding rock |
| stratovolcano(composite volcano) | a volcano that is composed of alternating layers of lava and pyroclastic material, along with abundant dikes and sills. Viscous, intermediate lava may flow from a central vent |
| subduction zone | a narrow, elongate region in which one lithospheric plate descends relative to another |
| syncline | a fold that is convex downward, or that hdad such an attitude at some stage in its development |
| tephra | a general term for all pyroclastic material |
| transform boundary | a plate boundary in which plates on opposite sides of the boundary move past each other in opposite directions |
| volcanic ash | the dust-sized, sharp edged, glassy particles resulting from an explosive volcanic eruption |
| volcanic cinder | a pyroclastic fragment, 0.5 to 2.5 cm in diameter, formed as magma spatters into the air during a volcanic eruption and cools as it fall to Earth |
| volcano | a vent in the surface of the Earth, from which lava, ash, and gases erupt, forming a structure that is roughly conical |
