Relative dating principles of rocks Sls chat line
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.
The basis for assuming that like fossils indicate contemporary formation is faunal succession.
However, as previously noted, times of volcanism and metamorphism, which are both critical parts of global processes, cannot be correlated by fossil content.
Correlation is, as mentioned earlier, the technique of piecing together the informational content of separated outcrops.
When information derived from two outcrops is integrated, the time interval they represent is probably greater than that of each alone.
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.fossil assemblages.
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.
Presumably if all the world’s outcrops were integrated, sediments representing all of geologic time would be available for examination.
This optimistic hope, however, must be tempered by the realization that much of the Precambrian record—older than 541 million years—is missing.