As these changes have occurred, organisms have evolved, and remnants of some have been preserved as fossils. Index fossils occur for a limited interval of time. Student Voices. For example, there is a specific interval of time, indicated by the red box, during which both the blue ammonite and orange ammonite co-existed. This allowed for erosional forces to expose rock that was buried long ago.
P ick up a rock, any rock, and examine it.
Dating Rocks and Fossils Using Geologic Methods
Therefore, by indexing their fossils, rocks, regardless of their composition or location, could be correlated with each other by when they were made. Quaternary Dating Methods. Email your Friend. Older methods of dating were more subjective, often an educated hypothesis based on the evidence available.