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Across 5. is an animal that lives part of its life on land and part of its life in water 6. is an animal with a backbone 9. a fossil must be widely distributed and represent a type of organism that existed only briefly 11. the magma cools and hardens into a mass of igneous rock 13. is a record of the life forms and geologic events in Earth history. 15. an extremely thin coating of carbonon rock 18. continents move very slowly over earth's because of force inside earth. 19. geologists divide the time between Precambrain Time and the present into three long units of time 20. is the type of rock that is made of hardened sediment 22. the surface where new rock layer meet a much older rock surface beneath them 24. is the gradual change in living things over long periods of time 26. a rock is the number of years since the rock formed 28. eras are subdivided into units of geologic time 29. is its compared to the ages of other rocks 30. if it no longer exists and will never again live on earth.

Down 1. to determine the relative ages of sedimentary rocks layers 2. have scaly skin and lay eggs with tough, leathery shell 3. is a warm-blooded vertebrate that feeds its young milk 4. are fossil in which minerals replace all or part of an organism 7. is a well-tested concept that explain a wide range of observations 8. is a hallow area in sediment in the shape of an organism or part of an organism 10. without a backbone 12. in which man types of living things became extint at the same time 14. is a soild copy of the shape of an organim 16. provide evidence of the activties of ancient organisms. 17. use fossils to build up picture of earth's past environments 21. lava that hardens on surface 23. are the preserved remain or traces of living things 25. is a break in Earth's crust 27. is a ball of dust and ice thats orbits the sun