Start 4 types of relative dating

4 types of relative dating

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.

In addition, its fossilized population should be sufficiently abundant for discovery to be highly probable.

Such an array of attributes represents an ideal, and much stratigraphic geology is rendered difficult because of departure of the natural fossil assemblage from this ideal.

In other words, the fossil species must have had a short temporal range.

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.

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

Smith’s geologic map was extremely crude, but in its effect on Earth study it was a milestone.

In dating the past, the primary value of fossils lies within the principle of faunal succession: each interval of geologic history had a unique fauna that associates a given fossiliferous rock with that particular interval.

The basic conceptual tool for correlation by fossils is the index, or guide, fossil.

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.

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