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Early Ideas About Impacts and Extinctions

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Article Posted: October 01, 1997

Now that cosmic impacts and their effects on evolution are widely accepted in the scientific community, it is interesting to look back at the origin of these ideas.



Without any doubt, the critical research was that done by Alvarez and collaborators, published in 1980, proposing that a major impact 65 million years ago caused the so-called K-T mass extinction, in which the dinosaurs and more than half the other species went extinct. This was the first scientific paper to provide hard data and a reasonable hypothesis to link impacts and extinctions. However, there were earlier suggestions, as reviewed here by Duncan Steel:

Who invented the idea that the dinosaurs met their denouement at the hands of a cosmic (asteroid or comet) impact? Numerous magazine articles have given the impression that such a hypothesis had its genesis in a paper published in 1980 by a team under Louis Alvarez, but this is simply not the case, the concept having a far longer history than just the past two decades.

As long ago as 1694 Edmond Halley suggested that impacts by comets were possible, a subject which he wrote he would "leave to be discussed by the studious of physical matters." The topic was taken up again in 1696 by William Whiston, by Thomas Wright of Durham in 1755, and the Marquis de Laplace in 1816, amongst others. The observed flux of comets, however, implied that such impacts had an annual probability of order just one in a hundred million, so that they might be dismissed.

The applecart was upset, however, when the nature of the Tunguska event in 1908 was recognized after the event, and at about the same time (in the 1930's) the first large Earth-crossing asteroids (ECAs) were discovered. The importance of ECAs in explaining the lunar (and terrestrial) cratering records was discussed in the 1940's in books published by Fletcher Watson and Ralph Baldwin. In a remarkable brief item in Popular Astronomy magazine in 1942, the great American meteoriticist Harvey Nininger went further: he suggested that asteroid impacts were responsible for geological boundary events and associated mass extinctions, controlling in part the evolution of life on Earth. But he did not specifically mention the dinosaurs.

Whilst palaeontologists have been known to complain of the incursion of physical scientists (such as the Alvarez team) into their territory, in fact one of the earliest suggestions of asteroids causing the dinosaurs' demise appeared in the Journal of Palaeontology in 1956. There M.W. De Laubenfels of Oregon State College scaled the effects of impacts up from what had happened at Tunguska, and imagined the dinosaurs being killed by the superheated winds thus generated. In 1958 Ernst Opik of Armagh Observatory suggested that geological boundaries were the result of asteroid impacts, and physical evidence for this (in the form of coincidences between tektite ages and the times of geological boundaries) was discussed in 1973 by Harold Urey, a matter taken up again in 1979 by British astronomers Victor Clube and Bill Napier who also considered the ages of dated terrestrial craters.

The earliest specific suggestion I have been able to find for asteroids killing the dinosaurs is a book which was privately published in 1953 in California by Allan O. Kelly and Frank Dachille under the title 'TARGET: EARTH - The Role of Large Meteors in Earth Science.' The authors identified such catastrophes as being the root cause - "The extinction of the great reptiles came about with a sudden change through the agency of cosmic collision" - although their mechanism was untenable; they believed that the Earth's spin axis was tilted in the impact with massive floods resulting.

Kelly and Dachille's book is also interesting in that they suggested that humankind would eventually need to develop the mechanisms to protect itself against catastrophes wrought by impacts: "This system will require perpetual surveillance of a critical envelope of space with the charting of all objects that come close to a collision course with the earth. It will require, further, that on discovery of a dangerous object moves be made to protect the earth."

Given that they were writing half a decade before Sputnik, one might imagine that Kelly and Dachille must be the inventors of this concept of 'planetary defence.' But not so. One has to go much further back, to 1822 when Lord Byron was residing in Pisa. Whilst taking a break from his poetical labours, Byron was moved to suggest the following:

"Who knows whether, when a comet shall approach this globe to destroy it, as it often has been and will be destroyed, men will not tear rocks from their foundations by means of steam, and hurl mountains, as the giants are said to have done, against the flaming mass? - And then we shall have traditions of Titans again, and of wars with Heaven."

MORE ON 19TH CENTURY CATASTROPHISM

Duncan Steel writes that a recent issue of New Scientist carried letter from him pointing out Lord Byron's suggestion in 1822 of the possibility (indeed, necessity) of diverting any comet found to be on a collision course with the Earth:

"Who knows whether, when a comet shall approach this globe to destroy it, as it often has been and will be destroyed, men will not tear rocks from their foundations by means of steam, and hurl mountains, as the giants are said to have done, against the flaming mass? - And then we shall have traditions of Titans again, and of wars with Heaven."

This is on page 185 in "Journal of the Conversations of Lord Byron: Noted during a Residence with his Lordship at Pisa, In the Years 1821 and 1822" by "Thomas Medwin, Esq., of the 24th Light Dragoons," printed for Henry Colburn, New Burlington Street, London, in 1824 (but with several later editions, usually labelled "Medwin's 'Conversations of Lord Byron'", in which the pagination would be different).

Steel continues: As a matter of fact the idea of cometary impacts was a recurrent theme in Byron's published writing, reflecting his belief that there had been many impact catastrophes in which previous inhabitants of the Earth had been wiped out. Byron viewed homo sapiens as being perhaps only temporarily in the ascendent (unless we manage to develop a defense system such as that he suggests in the quote above). Indeed on the page cited above he is also quoted as asking: "We are presently in the infancy of science. Do you imagine that, in former stages of this planet, wiser creatures than ourselves did not exist?"

Duncan Steel dis@a011.aone.net.au