Mass Extinctions

Oxygen deficiency in the oceans

Oxygen Caused Mass Extinction

We are all very much aware that oxygen deprivation leads quickly to death, and this is true not just of our own species but of virtually the whole organic world. There are indeed very few exceptions, such as the anaerobic bacteria that derive their energy from reducing sulphates to sulphides, which flourish in the absence of free oxygen. (As these organisms do not leave a fossil record they provide no clues for the geological detective.) Today the atmosphere never lacks oxygen, except in...

In search of possible causes of mass extinctions

When the subject of extinctions in the geological past comes up, nearly everyone's thoughts turn to dinosaurs. It may well be true that these long-extinct beasts mean more to most children than the vast majority of living creatures. One could even go so far as to paraphrase Voltaire and maintain that if dinosaurs had never existed it would have been necessary to invent them, if only as a metaphor for obsolescence. To refer to a particular machine as a dinosaur would certainly do nothing for its...

The likeliest causes

One thing that should be apparent by now is that it is extremely unlikely that there is a single overarching cause of mass extinctions, as propounded in the past by various scientists, such as Newell (marine regression), Stanley (climatic cooling), Raup (bolide impact), or Courtillot (volcanism), although all these factors seem to be implicated to some degree. Figure 9.1 presents in tabular form a list of the greater and lesser events that have been mentioned in this book, with in addition an...

Climatic effects of volcanic eruptions

Flood Basalt Provinces Volcano Clips

In New England, 1816 was called 'the year without a summer', with average temperatures in June 7 F (4 C) below normal. The consequence was serious crop failures. The situation was even worse in Europe disastrous crop failures led in places to famine, and the price of grain shot up dramatically. This unusual climate has been widely attributed to the eruption of Tambora in the Sunda Arc in the previous year. It should, however, be pointed out that there were other cold years in the early...

How catastrophic were massextinction events

Butler Tourism Model

Determining whether a given extinction event was catastrophic or merely gradual is not a straightforward matter, Table 3.1 The five biggest mass extinction events of the Phanerozoic The graptolites underwent the worst crisis in their history, and the conodonts were also severely affected. The dominant benthic (bottom-living) trilobites and brachiopods suffered major extinctions. (2) Late Devonian event (Frasnian-Famennian boundary) (22) Reef ecosystems, comprising rugose and tabulate corals and...

Is there a relationship between impacts and other massextinction horizons

After the success of the impact research agenda for the K-T boundary, great enthusiasm was expressed by some scientists that they had perhaps found the key, not just to the K-T event, but to all mass extinctions. This was certainly Luis Alvarez's hope, if not expectation, before he died, and the view of at least one distinguished palaeontologist, Dave Raup. In fact bolide impact was seized upon by many neo-catastrophists as a kind of deus ex machina. This Latin phrase, usually translated as...

Pulling the strands together

In drawing together the various strands we first need to ask how catastrophic, as opposed to merely calamitous, the various mass-extinction events were. As was indicated in Chapter 3, there is no way in which the stratigraphic record can ever provide dates that are precise to within less than a few thousand years. Thus, the connection between a bolide impact and a catastrophic phase of extinction lasting no longer than a few years could never be established with a high degree of confidence from...

What of the future

The sombre picture outlined above should dispel once and for all the romantic idea of the superior ecological wisdom of non-Western and pre-colonial societies. The notion of the noble savage living in harmony with Nature should be despatched to the realm of mythology where it belongs. Human beings have never lived in harmony with nature. If they caused less disturbance in earlier times it is because of the smaller size of populations and the more primitive technology available. As our world...

The evolutionary significance of mass extinctions

Darwin was firmly of the opinion that biotic interactions, such as competition for food and space - the 'struggle for existence' - were of considerably greater importance in promoting evolution and extinction than changes in the physical environment. This is clearly brought out by this quotation from The Origin of Species Species are produced and exterminated by slowly acting causes . . . and the most important of all causes of organic change is one that is almost independent of altered . . ....

Extinction periodicity or episodicity

Mention has already been made (in Chapter 3) of Jack Sep-koski's huge compendium of Phanerozoic marine families, which was the basis for the recognition with his colleague Dave Raup of the 'big five' mass-extinction events. Later on, using a combination of methods involving Fourier analysis and Monte Carlo simulation, they discovered to their great excitement a statistically highly significant 26 million-year periodicity in extinction events during the past 250 million years. This was a most...

The role of competition as perceived from the stratigraphic record

The type of competition that Darwin had in mind might be termed displacive competition, implying dynamic behaviour on the part of the newly arrived species or higher taxon in the wedge. How could this be recognized in the stratigraphic record One reasonable inference is that after the new taxon first appeared, it might progressively expand its abundance and diversity concomitant with the progressive reduction of its biologically most closely related or potentially competitive rival, known as...