Across
- 2. length of time required for half of the radioactive atoms in a sample to decay
- 5. changes in anatomy, phylogeny, and behavior that take place in clades larger than a single species
- 9. process by which unrelated organisms independently evolve similarities when adapting to similar environments
- 12. extinction caused by slow and steady process of natural selection
- 14. theory that proposes that eukaryotic cells formed from a symbiotic relationship among several different prokaryotic cells
- 15. the evolution of a species by gradual accumulation of small genetic changes over long periods of time
- 16. event during which many species become extinct during a relatively short period of time
- 17. scientist who studies fossils
- 19. division of geologic time into which eras are subdivided
Down
- 1. method of determining the age of a fossil by comparing its placement with that of fossils in other rock layers
- 3. process by which two species evolve in response to changes in each other over time
- 4. geologic processes, such as continental drift, volcanoes, and earthquakes, resulting from plate movement
- 6. major division of geologic time; usually divided into two or more periods
- 7. pattern of evolution in which long stable periods are interrupted by brief periods of more rapid change
- 8. distinctive fossil that is used to compare the relative ages of fossils
- 10. method for determining the age of a sample from the amount of a radioactive isotope to the nonradioactive isotope of the same element in a sample
- 11. process by which a single species or a small group of species evolves into several different forms that live in different ways
- 13. timeline used to represent Earth’s history
- 18. term used to refer to a species that has died out and has no living members