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Across 3. the geologic principle that states that in horizontal layers of sedimentary rock, each layer is older than the layer above it and younger than the layer below it 7. a scientist who studies fossil to learn about organisms that lived long ago 9. the process of determining the age of an object using half-life of one or more radioactive isotopes 10. a place where an old, eroded rock surface is in contact with a newer rock layer 11. the process by which all the different kinds of living things have changed over time 16. a type of fossil that provides evidence of the activities of ancient organisms 17. a break or crack in Earth’s lithosphere along which rocks move 18. one of the units of geologic time into which geologists divide eras 19. the type of rock that is made of hardened sediment 20. a fossil that is a copy of an organism’s shape formed when minerals seep into a mold 21. the age of a rock compared to the ages of rock layers 23. fossils of widely distributed organisms that lived only during a short period

Down 1. is a hypothetical supercontinent that included all current land masses, believed to have been in existence before the continents broke apart during the Triassic and Jurassic Periods. 2. a record of the geologic events and life forms in Earth’s history 4. an igneous rock layer formed when magma hardens beneath Earth’s surface 5. a fossil formed when an organism buried in sediment dissolves, leaving a hollow area 6. the gradual movement of the continents across the earth's surface through geological time. 8. an igneous rock layer formed when lava flows onto Earth’s surface and hardens 12. the age of rock given as the number of years since the rock formed 13. one of the three long units of geologic time between the Precambrian and the present 14. a core sample that is typically removed from an ice sheet 15. describes a type of organism that longer exists anywhere on Earth 22. the preserved remains or traces of living things