Furthermore, the environmental deterioration could have been effective in two ways. It could have been short-lived but so severe that only a limited proportion of organisms survived.
Hallam, A. (Anthony) 1933-
Alternatively it might have been less severe but more sustained in time so that, to quote T. Clearly this is highly rele- 6 In search of possible causes of mass extinctions vant to the subject of how catastrophic the mass-extinction events were, and the possible causal mechanism.
There are in fact only a few geological phenomena that can plausibly be invoked. The problem is to discriminate between them: one particular phenomenon can have multiple environ- mental effects on a global scale. Impacts by comets or asteroids, sea-level changes, and volcanism can all affect climate, and climatic change can affect sea level and the degree of oxygen- ation of the ocean water.
Catastrophes and Lesser Calamities : Tony Hallam :
Other writers have promoted one factor as the dominant, if not the only, cause of all mass extinctions, both major and minor. The approach preferred here is to attempt to steer a course, Odysseus-like, between the Scylla of one overriding cause and the Charybdis of an unresolved multiplicity of causes. A historical science like geology suffers from the limitation that it is not amenable to experimental test. Wording Edition.
What is MDS? LibraryThing's MDS system is based on the classification work of libraries around the world, whose assignments are not copyrightable.
MDS "scheduldes" the words that describe the numbers are user-added, and based on public domain editions of the system. Wordings, which are entered by members, can only come from public domain sources. A change of environment of mod- erate magnitude may be more important for mass extinction than one of extreme magnitude provided that the change is sustained long enough.
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To me the glass is half full rather than half empty. This is clearly brought out by this quotation from The Origin of Species: Species are produced and exterminated by slowly acting causes.
The face of Nature may be compared to a yielding surface, with ten thousand sharp wedges packed close together and driven inwards by incessant blows, sometimes one wedge being struck, and then another with greater force. The story behind the emergence of this name is an interesting one. At the beginning of the s the rather eccentric University of Chicago palaeobiologist Leigh Van Valen did some interest- ing research concerning the analysis of survivors of Phanero- zoic taxa which suggested that the probability of a fossil group becoming extinct was more or less constant in time.
To account for this, Van Valen put forward his Red Queen hypothesis.