Relative age dating geology

Posted by / 17-Aug-2017 05:44

Relative age dating geology

That is to say, it depends on other sequence-determining principles for establishing its validity.Suppose there exist a number of fossil-bearing outcrops each composed of sedimentary layers that can be arranged in relative order, primarily based on superposition.Almost without exception, the relative order of strata defined by fossils has been confirmed by radiometric ages.Correlation based on the physical features of the rock record also has been used with some success, but it is restricted to small areas that generally extend no more than several hundred kilometres.The first step is determining whether similar beds in separated outcrops can actually be traced laterally until they are seen to be part of the same original layer.Failing that, the repetition of a certain layered sequence (e.g., a black shale sandwiched between a red sandstone and a white limestone) lends confidence to physical correlation.On the practical side, an index fossil should be distinctive in appearance so as to prevent misidentification, and it should be cosmopolitan both as to geography and as to rock type.In addition, its fossilized population should be sufficiently abundant for discovery to be highly probable.

Following Smith’s pioneering work, generations of geologists have confirmed that similar and even more extensive fossil sequences exist elsewhere.This requires that the lifespan of the fossil species be but a moment of time relative to the immensity of geologic history.In other words, the fossil species must have had a short temporal range.Finally, the measurement of a host of rock properties may well be the ultimate key to correlation of separated outcrops.The more ways in which two rocks are physically alike, the more likely it is that the two formed at the same time.

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