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Across 2. gradual change in living things over long time periods 4. a break in Earth's crust 8. widely distributed fossil of organism that existed only briefly 9. preserved remains or traces of living things 12. always younger than rocks below it 13. number of years since a rock formed 15. well tested concept explaining wide range of observations 16. collect fossils; use information to study past life forms 18. extremely thin coating of carbon on rock 19. no longer exists; will never live on Earth again

Down 1. minerals replace all/part of an organism 3. type of rock made of hardened sediments 5. oldest layer of rock is at the bottom of any horizontal layer of rock 6. gap in geologic record; some rock layers lost due to erosion 7. solid copy of an organisms shape 10. evidence of activities of ancient organism; fossilized footprint 11. a hollow area in sediment in the shape of an organism 14. a rocks age compared to ages of other rocks 17. always younger than rock layers around/under it