Relative dating: 4/6/2021

This week I was able to further my understanding on relative dating. I am now able to look at layers of rock and determine which layer is the oldest. Relative dating gives geologists a rough estimate on when events in the past occurred. They do this by using principles developed by scientists such as Nicolaus Steno to determine the relationship between relative age and rocks. Listed below are the principals used to determine relative age.

The Law of Superposition: When observing un-deformed sedimentary rocks the oldest are on the bottom, and the youngest are on the top. 

Principle of original horizontality: Sedimentary rocks are nearly always horizontal when deposited. When they are not this is evidence of a shift in the earth's crust. 

Principle of lateral continuity: Sediments that are laterally continuous. As a result rocks that are similar are separated by a valley or other erosional features. 

Principle of crosscutting relationships: Features such as faults and igneous intrusions, which are younger than the rocks they cut through. 

Principle of inclusion: rocks that include intrusions of younger pre-existing rock which is younger than the rock from which the intrusion came. 

Principle of faunal succession: A period of time can be identified by fossilized plants or animals in definite order.  

Unconformity: An indication that sediment deposition was not continuous.

 

Activity: In class we were given several different examples of the principles listed above. The objective of this activity was to gain visual understanding of relative dating. The photos below are from the activity, and show the correct age of each layer.