Question

YOUNGEST TO OLDEST

Problem 1: Relative Time-What came first? The cross-section below shows the results of several geologic events. To the right of the diagram, list the sequences of geologic history starting with the oldest event and ending the youngest event. Present-day land surface S Youn o macho TR balts od bilo obes

Answer 1

Comparison between age of rock layers is done according to following principles:- Principle of Superposition Because of Earth's gravity, deposition of sediment will occur depositing older layers first followed by successively younger layers. Thus, in a sequence of layers that have not been overturned by a later deformational event, the oldest layer will be on the bottom and the youngest layer on top. This is the same principle used to determine relative age in the trash pits discussed previously. In fact, sedimentary rocks are, in a sense, trash from the Earth's surface deposited in basins, Principle of Original Horizontality Sedimentary strata are deposited in layers that are horizontal or nearly horizontal, parallel to or nearly parallel to the Earth's

surface, Sediment deposited on steep slopes will be washed away before it is buried and lithified to become sedimentary rock, but sediment deposited in nearly horizontal layers can be buried and lithified. Thus rocks that we now see inclined or folded have been disturbed since their original deposition, Principle of Original continuity If layers are deposited horizontally over the sea floor, then they would be expected to be laterally continuous over some distance. Thus, if the strata are later uplifted and then cut by a canyon, we know that the same strata would be expected to occur on both sides of the canyon. Look at the many photographs of the Grand Canyon in your textbook. Note that you can follow the layers all along the walls of the canyon, and you can find the same layers on both sides of the canyon. The

Grand Canyon is particularly good for this because different sedimentary rocks have different colors. Principle of Cross-cutting Relations Younger features truncate (cut across) older features. Faults, dikes, erosion, etc., must be younger than the material that is faulted, intruded, or eroded. So according to above principles, the order of given rock layers will be as following from youngest to oldest :- Youngest- S R J I #

G P N m L K F E D Q с B А Oldest