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Across 5. the age of rock compared to the ages of rock layers 6. a break or crack in Earth's lithosphere along which the rocks move 7. the remains or traces of living things preserved in rock 9. subdivisions of the periods of the geologic time scale 10. a place where an old, eroded rock surface is in contact with a new rock layer 12. a type of fossil consisting of an extremely thin black film 14. one of the three long units of geologic time between the Precambrian and the present 16. an igneous rock layer formed when lava flows onto Earth's surface and hardens 17. fossil that is a copy of an organism's shape 18. a fossil in which minerals replaced all or part of an organism 19. describes a type of organism that no longer exists anywhere on Earth 20. fossils tell the relative ages of the rock layers in which they occur

Down 1. one of the units of geologic time into which geologist divide eras 2. a type of rock that forms when particles from other rocks or the remains of plants and animals are pressed an cemented together 3. a type of fossil that provides evidence of the activities of ancient organisms 4. a scientist who studies fossils to learn about organisms that lived long ago 8. the process by which all the different kinds of living things have changed over time 11. a fossil formed when an organism buried in sediment dissolves, leaving a hollow area 13. the age of a rock given as the number of years since the rock formed 15. an igneous rock layer formed when magma hardens beneath Earth's surface