Across 1. a long, seismically active submarine ridge system situated in the middle of an ocean basin and marking the site of the upwelling of magma associated with seafloor spreading 3. 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 5. hot molten rock erupted from a volcano or fissure 6. the upper layer of the earth's mantle, below the lithosphere, in which there is relatively low resistance to plastic flow and convection is thought to occur 11. the outermost layer of a planet 16. A former “supercontinent” on the Earth. In the distant past a large landmass 17. a theory in geology: the lithosphere of the earth is divided into a small number of plates which float on and travel independently over the mantle and much of the earth's seismic activity occurs at the boundaries of these plates 18. liquid layer about 2,260 kilometers thick. It is made of iron and nickel 19. the rigid outer part of the earth, consisting of the crust and upper mantle 20. the process by which collision of the earth's crustal plates results in one plate's being drawn down or overridden by another 21. A tectonic boundary where two plates are moving away from each other and new crust is forming from magma that rises to the Earth's surface between the two plates

Down 1. hot fluid or semifluid material below or within the earth's crust from which lava and other igneous rock is formed by cooling 2. also known as a destructive plate boundary, is a region of active deformation where two or more tectonic plates or fragments of the lithosphere are near the end of their life cycle 4. a planar fracture or discontinuity in a volume of rock, across which there has been significant movement 7. objects which float on and travel independently over the mantle and much of the earth's seismic activity occurs at the boundaries of these objects 8. a liquid layer about 2,260 km thick composed of iron and nickel which lies above the Earth's solid inner core and below its mantle 9. A term, no longer used by geologists, that refers to the fact that continents are not stationary, but move across the Earth's surface 10. the innermost part of a core 12. 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 13. type of boundary where the two plates slide against each other in a sideways motion. 14. is the part of the earth between the core and the the crust 15. the quantity of mass per unit volume