Fossils/Geologic Time Quiz Review How do fossils form by replacement? Why do hard parts of organisms aid fossil formation? What conditions favor the preservation of a fossil? What organism lived on Earth during Precambrian time? What can cause an unconformity? A geologist finds a sequence of rock layers. She notices that a layer of limestone has a formation of granite that cuts through it. What do we call the granite that cuts through the limestone? And which rock is older? Which era is known as the age of dinosaurs and for the occurrence of the first mammals? Why is the record of geologic history most complete in the Cenozoic era? How are fossils useful? What is a fossil, and how is it different from a trace fossil? What does the principle of superposition state about layers of rock? During which era does the fossil record first contain fish? What is missing in a sequence of rock that contains an unconformity? What does extinct mean? What does endangered mean? What is an index fossil and what is the classic scientific example of one? What evidence best supports the theory that many species of organisms have become extinct? What is radioactive (radiometric) dating and what information does it give us? Why is radioactive dating better than the law of superposition in finding the age of a rock or fossil? Why is Precambrian time not broken down in to smaller periods of time? What is a gap in an area’s geologic history called? A major division in geologic time is called ___________________ which are broken down into ______________________ which are divided into _______________________ In the Cenozoic it is further divided into ____________________ then __________________ How old is the earth? How are geologic time periods divided? What type of scientists study fossils? What is an intrusion and what is the average age of the intrusion compared to the rocks it goes through? What geologic era are we currently in?