A trip through geological time

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