Blast From the Past

After the end Cretaceous extinction, small mammals scamper across the skull of a Tyrannosaurus rex. (diorama at the Canadian Museum of Nature, Ottawa)

I was recently reminded of a piece I once wrote, which was published in the newspaper about 17 years ago. I was interested in re-reading it and was sure it must be available somewhere online. Since a reasonably diligent search revealed no trace of it (and since I had a hard time even finding a paper copy), I thought I would post it here. It still bears some relevance and I thought some of you might enjoy it (though it was hard to resist the urge to revise the occasionally clunky phrasing!).

The Biggies Died Out in Earth’s Mass Extinctions

A while ago, a local area computer network at the University of Manitoba in Winnipeg was knocked out by a computer virus that went by a very melodramatic name – something like “Avenging Angel” or “Dark Destroyer.” The virus jumped from the network onto the hard drives of personal computers as their users plugged into and off the network. It spread rapidly, like an epidemic; once it was in a computer, it incapacitated any software the user attempted to open.

Nevertheless, one machine was not affected. This computer was an old IBM clone running a version of DOS (disk operating system) that was apparently too primitive for the virus to deal with. The computer had an inherent immunity to the infection.

The machine’s fortunate owner, a paleontologist and friend of mine, suggested that his computer was like the survivor of one of those mass extinctions that have occurred on Earth, in which most forms of life are driven to their deaths over a relatively brief period of geologic time. It seemed to be a particularly apt analogy.

Scientists have identified up to 15 mass extinctions in the history of life. The disappearance of dinosaurs (and many other life forms) at the end of the Cretaceous Period is by far the most widely known. Evidence indicates that this event was probably caused by the impact of a large asteroid on Earth 65 million years ago in what is now the Yucatan Peninsula of Mexico [n.b., the end of the Cretaceous is now placed at 66.0 million years ago, or Ma]. Such a collision of asteroid and planet could have caused earthquakes and tidal waves and produced a cloud of dust that blocked sunlight and caused the death of plants, the basis of food chains.

Although this was one of the five largest mass extinctions, it was not, in fact, the greatest one of all. That honour goes to the one that occurred at the end of the Permian Period about 250 million years ago [currently dated at about 252 Ma]. In this catastrophe up to 96 percent of all species on Earth became extinct.

The major mass extinctions apparently had different causes (the other three majors occurred in the Late Ordovician Period 440 million years ago [the extinction is currently dated at about 443-445 Ma]; the Late Devonian 360 million years ago [currently dated at about 372 Ma]; and the end of the Triassic 210 million years ago [currently dated at 201 Ma]. Some of the earlier global deaths may have resulted, not from bombardment by an object from space, but from changes in global climate, in glaciation, or in sea-level and ocean-circulation patterns. There was considerable variation in the length of time for global extinctions to take place. If the asteroid scenario is correct, then much of the end-Cretaceous event could have happened in less than a year, while other extinctions may have been spread out over several million years.

Over the past two decades, much research has been directed at mass extinctions. Scientists have discovered that in, in each of the events, certain types of life forms disappeared while others came to predominate among the survivors. Animals that died off were typically large and/or complex, and had specialized needs for food and resources – dinosaurs are typical of these. Those that survived tended to be small and had simple needs.

Other survivors had relatively low food needs. They may have produced very long-lived seeds or eggs or gone into a state of suspended animation. Thus, the simple clam-like invertebrate Lingula, which lives in the sediment of tidal flats and would probably be considered a pretty dull sort of animal, has survived every mass extinction of the past 500 million years.

Perhaps the comedian’s suggestion that the survivors of a future holocaust will be cockroaches driving Plymouth Valiants is not far off the mark, since both animals and cars could be described as ecologic generalists. Similarly, my friend’s computer is a simple “life form,” and was able to survive a deleterious event that knocked out the more complex and specialized members of the computer ecosystem.

A stand-alone computer is much less likely to be infected by a virus than is a computer cabled into a network. In the same way, biologic systems that are largely separated from the rest of Earth’s food web are unlikely to be severely affected by mass extinctions. For instance, the ecosystems along deep-sea ridges don’t depend on the sun for energy but are based on bacteria that metabolize energy from hot, mineral-rich water flowing out of the ridges. These ecosystems are characterized by strange, giant tube worms and unique bivalves and crabs. Such organisms were probably largely unaffected when the dinosaurs vanished.

Other stand-alone or nearly stand-alone ecologic systems include some large cave networks, and microbes that have been discovered living in bedrock deep within the Earth’s crust.

If we take the analogy further, and consider the whole Earth as a single local area network, we have to ask the obvious question: is there a virus lurking out there that could cause a global system failure? If there is, then the systems likely to be extinguished are the big complex ones, which sadly include any organism that can read this.

This piece was previously published as:

Young, G. 1997. The biggies died out in Earth’s mass extinctions. The Globe and Mail, Toronto, Saturday, Feb. 1, 1997, p. D6.

Young, G. 1998. The biggies died out in Earth’s mass extinctions. In, G. Dasgupta and J. Redfern (eds.), Reading Writing: Essay Strategies for Canadian Students, Second Edition. ITP Nelson, Scarborough (Ont.), p. 135-136.(reprinted from The Globe and Mail).

© Graham Young, 2014