Chapter 12 Geologic Time

4. Extinction of dinosaurs created an opportunity for mammals
10. subdivision of Eons
11. subdivision of an era
12. the surface where new rock layers meet a much older rock surface beneath them
13. Fossil must be widely distributed and existed only briefly
14. means that layers of sediment are generally deposited in a horizontal position
15. rock’s actual age, number of years since rock formed
17. rock’s age compared to the ages of other rocks
19. At beginning of this era a great number of different organisms evolved

1. sedimentary rocks, each bed is older than the one above it and younger than the one below it.
2. represent the greatest expanses of time
3. During first several hundred million years Atmosphere formed Oceans formed Continents began to form
5. lava/magma that hardens on the surface
6. forces and processes that we observe today have been at work for a very long time
7. preserved remains or traces of living things
8. type of rock that is made of hardened sediment
9. Reptiles very successful, age of Reptiles
13. is always younger than the rock layers around and beneath it
16. rate of decay that it takes for ½ of the radioactive atoms to decay to a stable isotope
18. subdivision of a period