Webcam female adult - What is relative dating geology

The diagram right shows two distinct faunal assemblages.What can be deduced from our two distinct faunas in terms of their usefulness in the relative dating of rocks?

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If the geological record was 100% complete and there were no breaks in sedimentation, the stratigrapher's job would be an easy one.

However, breaks in sedimentation do occur and when this happens, geologists' refer to this missing strata as an unconformity.

Typically commonly occurring fossils that had a widespread geographic distribution such as brachiopods, trilobites, and ammonites work best as index fossils.

If the fossil you are trying to date occurs alongside one of these index fossils, then the fossil you are dating must fall into the age range of the index fossil. In a hypothetical example, a rock formation contains fossils of a type of brachiopod known to occur between 410 and 420 million years.

Studying the layers of rock or strata can also be useful. If a layer of rock containing the fossil is higher up in the sequence that another layer, you know that layer must be younger in age. This can often be complicated by the fact that geological forces can cause faulting and tilting of rocks.

Absolute dating is used to determine a precise age of a rock or fossil through radiometric dating methods.

The Wheeler Formation has been previously dated to approximately 507 million year old, so we know the trilobite is also about 507 million years old.

But, how can we determine how old a rock formation is, if it hasn’t previously been dated?

So, often layers of volcanic rocks above and below the layers containing fossils can be dated to provide a date range for the fossil containing rocks.

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