A trip through geological time

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Across
  1. 1. a break in the earth's crust which rock moves
  2. 2. extinction when many types of living thing become extinct at one time
  3. 5. a type of fossil that is a hollow area in sediment in the shape of an organism
  4. 6. the time it takes for half of the atoms of a radioactive element to decay
  5. 8. fossil fossils of widely distributed organisms that lived during a geologically short time period
  6. 10. time scale a record of geological events and life forms in earth's history
  7. 12. a gap in the geological time period that shows where rock layers have been lost due to erosion
  8. 16. a person who studies fossil to learn about organisms that lived in the past
  9. 19. a cold-blooded vertebrate animal
  10. 20. a long period of time between the Precambrian and present periods
  11. 22. an animal with a backbone
  12. 25. an igneous rock layer formed when magma hardens beneath earth's surface
  13. 26. a vertebrate animal whose temperature is determined by the temperature of its environment
  14. 27. age the age of a rock given as the number of years since the rock formed
Down
  1. 1. preserved remains or traces of an organism that lived in the past
  2. 3. a group of organism that no longer live and will not live ever again
  3. 4. a collection of ice and dust that orbits the sun
  4. 7. the change over time
  5. 9. fossil a type of fossil that provides evidence of the activities of ancient organisms
  6. 11. an animal without a backbone
  7. 13. decay the process where nuclei of radioactive elements break down releasing fast moving particles and energy
  8. 14. of superposition a basic law of geochronology stating that in any undisturbed sequence of rocks deposited in layers, the youngest layer is on top and the oldest on bottom, each layer being younger than the one beneath it and older than the one above it.
  9. 15. age the age of a rock compared the the age of other rocks
  10. 17. fossil a fossil that materials replace all or part of an organism
  11. 18. a fossil that is a solid copy of the organism shape
  12. 21. film a type of fossil consisting of an extremely thin coating of carbon on the rock
  13. 23. an igneous rock formed when lava flows onto earth's surface and hardens
  14. 24. a length or portion of time