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Across 3. a sign of photsynethic life 6. inactive or asleep 8. the wearing away of a planet's surface by natural forces 12. liquid rock 14. a type of rock that forms by being compressed or cemented into solid layers 15. a rock from space that that has landed on Earth 16. the red planet that we have been studying 21. crushed rock fragments thrown in all directions when a impact crater is formed 22. someone who studies life that can be seen only through a microscope 23. the planet that we live on 24. the study of how a planet's crust moves, folds and cracks

Down 1. a type of rick that forms from hot melted rock, that cools and becomes solid 2. the ability to do work (pg. 86) 4. pertaining to life 5. real life models that scientists use 7. tiny, microscopic life 9. a type of extreme environment 10. vitamins, minerals and other raw materials that living things need 11. a starting measurement that a scientist uses for an experiment 12. a type of rock that is formed from igneous or sedimentary rocks by high temperatures 13. evidence that life was present 17. without oxygen 18. the traces or remains of a living organism 19. a rock flying through space 20. with oxygen