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Unit 6 earth forces relative dating

The principle of cross-cutting relationships pertains to the formation of faults and the age of the sequences through which they cut.Faults are younger than the rocks they cut; accordingly, if a fault is found that penetrates some formations but not those on top of it, then the formations that were cut are older than the fault, and the ones that are not cut must be younger than the fault.

These strata make up much of the famous prominent rock formations in widely spaced protected areas such as Capitol Reef National Park and Canyonlands National Park.

From top to bottom: Rounded tan domes of the Navajo Sandstone, layered red Kayenta Formation, cliff-forming, vertically jointed, red Wingate Sandstone, slope-forming, purplish Chinle Formation, layered, lighter-red Moenkopi Formation, and white, layered Cutler Formation sandstone.

Photo from Glen Canyon National Recreation Area, Utah.

Relative dating is the science of determining the relative order of past events (i.e., the age of an object in comparison to another), without necessarily determining their absolute age, (i.e. In geology, rock or superficial deposits, fossils and lithologies can be used to correlate one stratigraphic column with another.

The regular order of the occurrence of fossils in rock layers was discovered around 1800 by William Smith.

While digging the Somerset Coal Canal in southwest England, he found that fossils were always in the same order in the rock layers.For example, in sedimentary rocks, it is common for gravel from an older formation to be ripped up and included in a newer layer.A similar situation with igneous rocks occurs when xenoliths are found.The principle of original horizontality states that the deposition of sediments occurs as essentially horizontal beds.Observation of modern marine and non-marine sediments in a wide variety of environments supports this generalization (although cross-bedding is inclined, the overall orientation of cross-bedded units is horizontal).As he continued his job as a surveyor, he found the same patterns across England.He also found that certain animals were in only certain layers and that they were in the same layers all across England.Methods for relative dating were developed when geology first emerged as a natural science in the 18th century.Geologists still use the following principles today as a means to provide information about geologic history and the timing of geologic events.Due to that discovery, Smith was able to recognize the order that the rocks were formed.Sixteen years after his discovery, he published a geological map of England showing the rocks of different geologic time eras.

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