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Across 2. The process of determining the age of an object using half-life of one or more radioactive isotopes 5. A scientist who studies fossils to learn about organisms that lived long ago 8. A fossil formed when an organism buried in sediment dissolves, leaving a hollow area 9. A place where an old, eroded rock surface is in contact with a newer rock layer 10. The type of rock that is made of hardened sediment transported by water; fossils are found in this type of rock 11. The age of rock compared to the ages of rock layers 13. Fossils of widely distributed organisms that lived only during a short period, used to define and identify geologic time periods 16. The preserved remains or traces of living things 17. An igneous rock layer formed when lava flows onto Earth’s surface and hardens

Down 1. 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 3. The age of rock given the number of years since the rock formed 4. A fossil that is a copy of an organism’s shape formed when minerals seep into a mold 6. An igneous rock layer formed when magma hardens beneath Earth’s surface 7. A type of fossil that provides evidence of the activities of ancient organisms 12. The process by which all the different kinds of living things have changed over time 14. Describes a type of organism that no longer exists anywhere on Earth 15. A break or crack in Earth’s lithosphere along which rocks move