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Across 1. The spherical mass, largely metallic iron, at the center of the Earth. (Core) 2. The science of our planet. (Geology) 4. Any system that has a boundary that prevents the passage in or out of energy and matter. (Isolated System) 9. Any system with a boundary that allows the passage in or out of energy but not of matter. (Closed System) 10. The layer of the mantle where rocks are relatively ductile and are easily deformed. It lies at a depth of 100 to 350 km below the surface. (Athenosphere) 13. The crust between the oceans. (Oceanic Crust) 14. The seismic discontinuity that marks the base of the crust. (Moho) 17. The part of the Earth’s crust that comprises the continents, which has an average thickness of 45 km. (Continental Crust) 19. The study of the processes that operate at or beneath the surface of Earth, and the materials on which those processes operate. (Physical Geology) 20. A hypothesis that has been examined and found to withstand numerous tests. (Theory) 21. The assemblage of all of Earth’s parts and the relationships between them. (Earth System) 22. The thick shell of dense, rocky matter that surrounds the core. (Mantle) 23. Any system that has a boundary that allows the passage in or out of both energy and matter. (Open System) 24. The outer 100 km of solid Earth, where rocks are harder and more rigid than those in the plastic athenosphere. (Lithosphere)

Down 1. The outermost and thinnest of Earth’s compositional layers, which consists of rocky matter that is less dense than the rocks of the mantle below. (Crust) 2. The view that speciation proceeds by imperceptibly small, cumulative steps over long periods of time rather than by abrupt, major changes. (Gradualism) 3. Grand unifying theory of geology saying that Earth’s outermost 100km “eggshell” (the lithosphere) is cracked, composed of about a dozen pieces (“plates”), which float on the hot, deformable athenoshpere, moving ponderously in various directions, spreading apart, slowly colliding, and grinding past another. (Plate Tectonics Theory) 5. The use of evidence that can be seen and tested by anyone who has the means to do so, consisting often of observation, formation of a hypothesis, testing of the hypothesis and formation of a theory, formation of a law, and continued reexamination. (Scientific Method) 6. The primary unit in a time-stratigraphic sequence of rocks. (System) 7. The central, solid portion of Earth’s core. (Inner Core) 8. The outer portion of Earth’s core, which is molten. (Outer Core) 11. Of, relating to, or involving a catastrophe. (Catastrophic) 12. An unproved explanation for the way things happen. (Hypothesis) 15. A statement that some aspect of nature is always observed to happen in the same way and that not deviations have ever been observed. (Principle) 16. A narrow, well-defined zone of deep earthquake foci beneath a sea floor. (Benioff Zone) 18. A scientific statement that some aspect of nature is always observed to happen in the same way and that no deviations have ever been seen. (Law)