Relative Dating and Biostratigraphy

Relative Dating

Understand that relative dating involves placing geological events into a sequence without knowing their numerical age
Familiarize yourself with the Principle of Original Horizontality: layers of sediment are generally deposited in a horizontal position
Review the Principle of Superposition: in an undisturbed sequence of sedimentary rocks, the youngest rocks are at the top and the oldest at the bottom
Grasp the Principle of Cross-Cutting Relationships: a geologic feature or rock formation that cuts across other layers or features is younger than the layers or features that it cuts across
Understand the Principle of Inclusions: if one rock body contains fragments of another rock body, it must be younger than the fragments of rock it contains
Learn about unconformities, which indicate a period where deposition ceased, erosion removed previously formed rocks, and then deposition resumed
Explore the use of relative dating to interpret the geological history of an area

Biostratigraphy

Be aware that biostratigraphy is a branch of stratigraphy which uses fossil evidence to date rock strata
Recall that biostratigraphy relies on the Principle of Faunal Succession: the idea that specific groups of fossil organisms existed only for a fixed span of time
Understand the concept of Index Fossils: these are fossils of widely distributed organisms that lived during only one particular, short time period. They are used as markers to identify the relative age of rock layers
Become familiar with the process of correlation, it involves linking rocks from different places based on their age and the characteristics they share
Comprehend fossil assemblages, it refers to the group of different species found in the same layer of rock
Realize the importance of biostratigraphy in interpreting Earth’s history, in determining relative ages of rocks, and in the study of past life forms

Revise these principles and try to understand how they help scientists interpret the Earth’s past and decipher its complex history. Always try to relate back to real world examples to deeply understand these principles.