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Across 4. A theory that explains scientific observations; 8. A solid sphere in the middle of the fluid core 11. The solid, outermost layer of the Earth, lying above the mantle 13. The concept that new oceanic crust is created at the mid-ocean ridge as a result of divergence between plates. 18. The gradual movement of the continents across the earth's surface 21. Seismic waves are waves of energy that travel through the core of the earth. 22. A continent formed 250 million years ago due to plate movement. 23. The outer solid part of the earth, including the crust and uppermost mantle 25. A crack in the earth's crust 26. for measuring the water's depth by emitting sound pulses 27. The mass per unit volume of a substance at a specified pressure and temperature

Down 1. a linear feature that exists between two tectonic plates that are moving away from each other 2. Pressure is the force per unit area applied to a direction perpendicular to the surface of the object. 3. Two plates of the lithosphere coming closer together from two different directions 5. The process by which sound waves travel through a medium. 6. A boundary in which two plates slide past each other without creating or destroying lithosphere 7. A current in a fluid that results from convection 9. A long, narrow, but very deep depression in the ocean floor 10. The site where tectonic plates move apart and new oceanic crust is created 12. A liquid layer about 2,260 kilometers thick 14. The theory that the earth's surface is divided into a few large, thick plates that are continually moving 15. he sideways and downward movement of the edge of a plate of the earth's crust into the mantle beneath another plate. 16. A zone of the earth's mantle that lies beneath the lithosphere 17. a valley with steep sides; formed by a rift in the earth's crust 19. The emission of energy as electromagnetic waves or as moving subatomic particles. 20. The layer of the Earth between the crust and the outer core 24. one of the sections of the earth's lithosphere, constantly moving in relation to the other sections.