Absolute dating of a fossil

Using fossils simply for identification purposes, Smith constructed a map of the various surface rocks outcropping throughout England, Wales, and southern Scotland.

With the development of miniaturized analytical equipment, evaluation of rock properties down a small drill hole has become possible.

The technique, called well logging, involves lowering a small instrument down a drill hole on the end of a wire and making measurements continuously as the wire is played out in measured lengths.

Ideally, an index fossil should be such as to guarantee that its presence in two separated rocks indicates their synchroneity.

This requires that the lifespan of the fossil species be but a moment of time relative to the immensity of geologic history.

From an examination of such outcrops with special focus on the sequence of animal forms comes the empirical generalization that the faunas of the past have followed a specific order of succession, and so the relative age of a fossiliferous rock is indicated by the types of fossils it contains.

As was mentioned at the outset of this article, fossil assemblages.

Following Smith’s pioneering work, generations of geologists have confirmed that similar and even more extensive fossil sequences exist elsewhere.

To this day, fossils are useful as correlation tools to geologists specializing in stratigraphy.

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.

Finally, the measurement of a host of rock properties may well be the ultimate key to correlation of separated outcrops.

Presumably if all the world’s outcrops were integrated, sediments representing all of geologic time would be available for examination.

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