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Mass extinctions, or not?



Definition: Mass extinctions are defined as a major extinction event, typically marked by the loss of 10% or more of families, and 40% or more of species, in a short time (M.Benton, D.Harper 1997)

Within geological time, one million years can be thought of as a second in our day. This helps enable you to imagine the enormous period that has passed, without anyone really noticing the effect that one million years has had on the history of earth.

One theory that is of importance when looking into mass extinction causes is the error that may be incurred from not taking into account the limitations of the geological time scale. It is this knowledge that has led to more and more constraints gradually being placed on the time scale due to ever more accurate dating of boundaries and the fossils found within strata found all around the world (A.Hoffman, 1989). A.Hoffman believes that the classification of mass extinction has been used too freely and therefore certain events have not been described correctly. This is directly related back to the problems associated with the geological time scale mentioned earlier.

It is plausible that certain ‘mass extinctions’ may in fact be nothing else than clusters of smaller extinction events, which occurred within a relatively short period of geological time. This is not to say, all mass extinctions follow this new thinking, but it may be worth considering this possibility, as so often the easy explanation is used when really the answer is complex, and not catastrophic.

Catastrophism began in the early 19th century, devised by Georges Cuvier, when he observed several large faunal gaps within the strata of the Paris basin. However, Charles Lyell did not agree with catastrophism, but founded the idea of gradualism. The gradualistic approach of Lyell became unacceptable as an explanation for certain phenomena during the 20th century as advances in dating and continuing research proved that time periods, were too small for anything but a catastrophic event to wipe out the amount of creatures observed. In contradiction, to the last point is the idea that the clusters of smaller extinctions mentioned earlier. These smaller extinction events are probably triggered by separate causal factors and therefore, no, one cause can be blamed as the trigger of a mass extinction if the observed biotic decrease occurs as a series of events, within a short period of time according to Hoffman.

In an interview with Palaeontologist Dr Richard Twitchett of Bristol University, the following question was asked…

Question: What future work would you like to see, or undertake to enable a more conclusive cause of the observed biotic decrease at the Triassic/Jurassic boundary?

Answer: “there are several factors that need to be considered, all of which boil down to accurate dating; i.e. the quality of the fossil record, trace fossils and linking evidence from the land with evidence from the sea. This is where the work should and is being focussed at the moment.”

  N.B see Other related sites on the IGCP Project 458 for the latest research on the T/J boundary  

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