Dating of dinosaur fossils

As an example of how they are used, radiometric dates from geologically simple, fossiliferous Cretaceous rocks in western North America are compared to the geological time scale.To get to that point, there is also a historical discussion and description of non-radiometric dating methods.The layers of rock are known as "strata", and the study of their succession is known as "stratigraphy".Fundamental to stratigraphy are a set of simple principles, based on elementary geometry, empirical observation of the way these rocks are deposited today, and gravity.It can't float in mid-air, particularly if the material involved is sand, mud, or molten rock.The principle of superposition therefore has a clear implication for the age of a vertical succession of strata.Both were avialans - dinosaur-birds that diverged millions of years ago from the theropods of land dinosaurs such as the Tyrannosaurus Rex and the velicoraptor The fossilised skeleton of the Aurornis xui bird was found in a quarry in the Liaoning Province in China, near the North Korean border.

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In order for a layer of material to be deposited, something has to be beneath it to support it.However, note that because of the "principle of cross-cutting relationships", careful examination of the contact between the cave infill and the surrounding rock will reveal the true relative age relationships, as will the "principle of inclusion" if fragments of the surrounding rock are found within the infill.Cave deposits also often have distinctive structures of their own (e.g., spelothems like stalactites and stalagmites), so it is not likely that someone could mistake them for a successional sequence of rock units. Each of them is a testable hypothesis about the relationships between rock units and their characteristics.An early summary of them is found in Charles Lyell's .In no way are they meant to imply there are no exceptions.

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