Geologic Time Scale

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Across
  1. 2. Layers of sedimentary rock that are stacked on top of each other, with each layer representing a different period of time.
  2. 9. The process by which an unstable atomic nucleus emits radiation and transforms into a more stable form.
  3. 10. A scientist who studies the fossil record to understand the evolution and diversity of life on Earth.
  4. 12. A scientist who studies human history and prehistory through the excavation and analysis of artifacts and other physical remains.
  5. 15. A division of geological time that is shorter than an era and longer than a period.
  6. 16. A major division of geological time, lasting tens or hundreds of millions of years.
  7. 17. The time it takes for half of the atoms in a sample of a radioactive substance to decay.
  8. 19. A solid piece of debris from space that survives its passage through Earth's atmosphere and strikes the ground.
  9. 20. Fossils that are used to determine the relative age of rock layers and geological events because they are characteristic of a particular time period and widespread geographically.
Down
  1. 1. A period of time during which a significant portion of Earth's species become extinct in a relatively short period of time.
  2. 3. A process of fossilization in which mineral-rich groundwater permeates porous organic material and replaces it with minerals, preserving its shape and structure.
  3. 4. The process by which organic remains become preserved as fossils through a variety of physical and chemical processes.
  4. 5. A bowl-shaped depression in the ground created by a meteorite impact, volcanic activity, or other geological processes.
  5. 6. A division of geological time that is longer than an epoch and shorter than an era.
  6. 7. The process by which organic material is preserved in sedimentary rock through the partial or complete loss of water and other volatile compounds, leaving behind a thin film of carbon.
  7. 8. A term used to describe the unstable atomic nuclei of certain elements that emit radiation as they decay into more stable forms.
  8. 11. A major division of geological time, lasting hundreds of millions or billions of years.
  9. 13. A cylindrical sample of rock or sediment that is obtained by drilling vertically into the ground.
  10. 14. The actual age of a rock or fossil measured in years.
  11. 18. A mark or imprint left by an organism or object in sedimentary rock, such as a footprint or leaf impression.