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Across 3. the true age of a rock or fossil 5. the concept that the Earth’s surface was shaped in the past by gradual processes, such as erosion, and by small sudden changes, such as earthquakes, like the processes we see today rather than by sudden catastrophic acts 7. a plant, animal or other organism that is perfectly preserved for many years 9. gives important information about past life and environments on Earth 11. a geological law that states in any undisturbed sequence of rock layers the youngest layer is on the top and the oldest layer is on the bottom 12. formed when a mold fossil fills up with sediment; three dimensional (3D) 14. preserved remains or traces of animals, plants and other organisms from the remote pass 16. the time taken for the radioactivity of a specified isotope to fall to half its original value 17. fossils that are used to define and identify geologic time periods 18. evidence of plants, animals and other organisms in the form of preserved footprints, tracks, burrows, borings and feces left behind rather than the actual organism’s remains

Down 1. “turned to stone,” a fossil in which minerals replace all or some of an organism 2. the rate of decay of unstable isotopes can be used to estimate the absolute ages of fossils and rocks 4. the theory that major changes in the Earth’s crust result from sudden catastrophes, such as the impact of a large meteor, rather than from gradual evolutionary processes 6. the remains of plants animals and other organisms are converted into a carbon or carbon-containing residue 8. a gap in the sequence of rock layers; the surface where new rock layers meet a much older rock surface beneath them 10. the geologic age of a fossil organism, rock or geologic feature or event defined relative to other organisms, rocks, or features or events rather than in terms of years 13. formed when an object is placed into soft mud and is removed by decomposition or physical sources 15. a group of extinct segmented hard shelled marine arthropods that lived over 520 million years ago