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Across 1. a fossil that is a copy of an organism’s shape formed when minerals seep into a mold 5. an igneous rock layer formed when lava flows onto Earth’s surface and hardens 8. an igneous rock layer formed when magma hardens beneath Earth’s surface 10. fossils of widely distributed organisms that lived only during a short period, used to define and identify geologic time periods 12. the age of rock given as the number of years since the rock formed 13. the preserved remains or traces of living things 14. the process of determining the age of an object using half-life of one or more radioactive isotopes 15. the process by which all the different kinds of living things have changed over time 16. a break or crack in Earth’s lithosphere along which rocks move 17. describes a type of organism that longer exists anywhere on Earth

Down 2. 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. a type of fossil that provides evidence of the activities of ancient organisms 4. the type of rock that is made of hardened sediment that is transported by water 6. a scientist who studies fossil to learn about organisms that lived long ago 7. a place where an old, eroded rock surface is in contact with a newer rock layer 9. a fossil formed when an organism buried in sediment dissolves, leaving a hollow area 11. the age of a rock compared to the ages of rock layers