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Across 3. One of the units of geologic time into which geologists divide eras 5. An era than spans about 66 million years ago also known as the age of mammals 7. A record of the geologic events and life forms in Earth’s history 8. The era of time prior to 600 million years ago, covering 90% of Earth’s history 13. The gradual movement of the continents across the earth's surface through geological time. 14. Atoms of the same element that have the same number of protons but different numbers of neutrons 16. One of the three main rock types and formed from the cooling and solIdification of magma and lava 17. A hypothetical supercontinent that included all current land masses, believed to have been in existence before the continents broke apart during the Triassic and Jurassic Periods.

Down 1. An interval of time known as the age of reptiles from about 252 to 66 million years ago 2. The rate of decay of unstable isotopes can be used to estimate the absolute ages of fossils and rocks 4. A core sample that is typically removed from an ice sheet 6. Rocks that are subjected to high heat and pressure which causes a profound change in form 9. A continuous process by which rocks are created changed from one form to another, destroyed, and then formed again 10. “Turned to stone”, a fossil which minerals replace all or some of an organism 11. The era which ran from about 542 million years to 251 million years ago, know for a great change on Earth with plants becoming widespread and the first vertebrate animals colonizing land. Also known for the breakup of the supercontinent 12. A group of extinct segmented hard-shelled marine arthropods that lived over 520 million years ago 15. A record of the geologic events and life forms in Earth’s history