The potential problem with any research paradigm is the radical premise upon which it builds. If this footing slips the foundation crumbles, and an edifice of thought construct comes tumbling down. Sir Charles Lyell, like his philosophical model James Hutton, simply could not conceive of a deity so indifferent or incompetent as to allow global catastrophes to occur. Lyell had a particular disdain for speculation on comet induced upheavals. References to these hoary threats are not indexed in "Principles" and when mentions of hypothetical comet caused catastrophes do appear in Lyell's work they are treated in a flippant condescending fashion. A bit of the barrister shows through clearly here, Lyell was making his case. There is irony in the timing of Lyell's quest to establish an only gradually changing motif for our world with its " . . . perfect harmony of design and unity of purpose." The very year (1827) Lyell first carried his preliminary manuscript to the publisher there was in progress a contest sponsored by the University of Edinburgh for the "best Essay on Comets." The winner of the gold medal and fifty pounds was David Milne who produced a superb overview of what was then known of comets. The work was published in 1828 under the title of Essay On Comets. Milne reviews earlier ideas about comets and sequentially dismisses all previous hypotheses on extraterrestrially-induced catastrophe with the exception of one, a direct impact or very, very close brush with our planet. He goes on to identify the then recently (1818) discovered comet, Pons/Encke, as a likely candidate for such a smashup. Referring to Olbers calculations, Milne informs his readers that this comet will come as close to Earth as the moon in 88,000 years, miss the planet by 7,700 miles after 4 million years and finally hit with enough energy to annihilate species in 219 million years. The way Milne ends this part of his essay is rather prophetic:
"I have remarked, that Encke's Comet approaches nearer the earth's orbit than any other yet discovered; and hence the probability is, that the fate which is thus demonstrated to be reserved for our globe, will be fulfilled by means of this particular Comet. But such speculations, however striking the results, conduce to no practical advantage, and contribute little to the advancement of science. They afford astonishing proofs of the energy of man's intellectual power, by which he extends his vision to the horizon of the most distant futurity, and looks forward, it may be, with a feeling of complacent assurance, to those momentous events, which, from his knowledge of nature, he is enabled to foresee. But let him not rest too confidently on the verity of such anticipations. Astronomers have prophesied, it is true, the collision of a Comet with the earth; an event that will at once destroy the greater part of the human species: but any slight attraction, which, in calculating the movements of this comet, they have chanced to overlook, must invalidate all their conclusions, and render the prediction at once vain and futile; while, perhaps, some other comet, among the many thousands traversing the system, and following an orbit to us unknown, may, in the mean while, come in contact with our globe, and thus, without any warning of its approach, produce the same terrible effects, long before the expected period ha[s] arrived."
So there was within the public domain a very scientific demonstration, based on observation and the "clockwork" laws of Newtonian physics, that Earth could be hit by a comet, no divine hand had designed this possibility out as Hutton and Playfair had maintained.
"The Author of Nature has not given laws to the universe, which, like the institutions of men, carry in themselves the elements of their own destruction. He has not permitted in His works any symptom of infancy or of old age, or any sign by which we may estimate either their future or their past duration. He may put an end, as He no doubt gave a beginning, to the present system, at some determinate period of time; but we may rest assured that this great catastrophe will not be brought about by the laws now existing, and that it is not indicated by any thing which we perceive."
This statement first appeared in volume IV on page 55 of Playfair's Works (1822) sans italics. The above quote is taken from "Principles" of Geology (1850); the highlighting is Lyell's.
Quite likely Lyell never perused Milne's fine essay; from 1828 through 1831 he was busy traveling about Europe gathering evidence for his own case, and he spent a few more years completing "Principles." If Lyell was aware of Milne's work he certainly gave it no credence for the concluding remarks of "Principles" read very much like those of Hutton/Playfair quoted above.
So compelling was Lyell's stately view of nature that associations between comets and meteor showers, combined with only nucleus size limiting data from observing a few comets during solar transit, sufficed to completely ephemeralize these hairy demons in the minds of most scientists. The obvious crack in the very foundation of the gradualist paradigm was thus quietly patched over. This is well illustrated by a note which appeared in the February 15,1872 issue of "Nature" (Vol. 5, pg. 310):
"We have reason to know that many weak people have been alarmed, and many still weaker people made positively ill, by an announcement which has appeared in almost all the newspapers, to the effect that Prof. Plantamour, of Geneva, has discovered a comet of immense size, which is to "collide," as our American friends would say, with our planet on the 12th of August next. We fear that there is no foundation whatever for the rumour. In the present state of science nothing could be more acceptable than the appearance of a good large comet, and the nearer it comes to us the better, for the spectroscope has a long account to settle with the whole genus, which up to this present time has fairly eluded our grasp. But it is not too much to suppose that the laymen in these matters might imagine that discovery would be too dearly bought by the ruin of our planet. Doubtless, if such ruin were possible, or indeed probable--but let us discuss this point. Kepler, who was wont to say that there are as many comets in the sky as fishes in the ocean, has had his opinion endorsed in later times by Arago, who has estimated the number of these bodies which traverse the solar system as 17,500,000. But what follows from this? Surely that comets are very harmless bodies or the planetary system, the earth included, would have suffered from them long before this, even if we do not admit that the earth is as old as geologists would make it. But this is not all. It is well known that some among their number which have withal put on a very portentous appearance are merely the celestial equivalents of our terrestrial "wind-bags"..."
By the way according to Milne:
". . . Kepler, who, though in some measure the father of modern astronomy, . . . had very incorrect notions respecting the system of nature in general. The planets he imagined to be animals swimming round the sun by means of fins acting upon the ethereal fluid; and, agreeable to this strange belief, he held Comets to be also huge uncommon creatures, generated in the celestial spaces, and that they "were made to the end, the ethereal fluid might not be more void of monsters, than the ocean is of whales, and other great thieving fishes; and that a gross fatness being thus gathered together, as excrements into an apostume, the ethereal medium might thereby be purged, lest the sun should be obscured, as he was for a year together, when Julius Caesar was slain; when being weakened by a bloody colour, he cast but a dim and disdainful light!" He even supposes that the faculty of the earth, which he fancied to be animated like all the other planets, is so terrified at the approach of a comet, that it "sweats out a great quantity of vapour through terror, and that hence arise great rains and floods."
Milne extracted this from Kepler's Harmonices Mundi, (1619 Tab. IV, Cap.VII). Though Kepler's views were at odds with earlier thinkers such as Lucretius of the Epicurean school they show the need people have to rationalize what is observed. Comets appear animate therefore they are alive, or as we have read above, the Earth does not appear to have been harmed by a comet though many must have collided, therefore comets cannot hurt Earth.
It is useless to speculate on how the investigation of Earth's past would have transpired had not the gradualist motif been adopted; what is important is the recognition of false constructs based on this premise. Darwin, who built his case upon Lyell's, felt that:
"Psychology will be based on a new foundation, that of the necessary acquirement of each mental power and capacity by gradation."
So Darwin's ideas provided investigators not only missing links to look for in Lyell's missing chapters, researchers also had to be on the look out for signs of missing marbles in earlier or obviously still 'primitive' cultures. This premise of gradual mental evolution made it far too easy to casually brush aside or reinterpret observations that were either handed down through time or unearthed from an earlier era. Such reassessments were particularly likely if the described phenomena fell outside scientifically observed natural processes. In general the ancients were viewed as poor observers prone to exaggeration. A translator reading an archaic description of a Tunguska type event had little trouble seeing such as a poetic description of a jolly good storm. Contemporary investigators working with a different premise and broader knowledge of natural phenomena can sometimes get around these translation errors simply by comparing the results of earlier researchers. An excellent example of ferreting such errors by this method comes from a direct comparison of an 1899 (M.S. Terry) and 1918 (H.N. Bate) translation of The Sibylline Oracles. These lines come from Book V:
And then incensed shall God the imperishable, who dwells on high, hurl thunderbolts from heaven down on the head of him that is impure and IN THE PLACE OF WINTER THERE SHALL BE IN THAT DAY SUMMER. And to mortal men shall then be great woe; for the Thunderer shall utterly destroy all shameless men and with his thunders and with lightning-flames and blazing thunderbolts men of ill-will, and thus shall he destroy the impious ones, so that there shall remain upon the earth dead bodies more in number than the sand. (M.S. Terry 1899, 1973 ed.)
"And then in his anger the immortal God who dwells on high shall hurl from the sky a fiery bolt on the head of the unholy and SUMMER SHALL CHANGE TO WINTER IN THAT DAY. And then great woe shall befall mortal men: for He that thunders from on high shall destroy all the shameless, with thunderings and lightnings and burning thunderbolts upon his enemies, and shall make an end of them for their ungodliness, so that the corpses shall lie on the earth more countless than the sand." (H.N. Bate 1918)
Obviously both of the highlighted lines cannot be correct. Terry's version, based largely on the work of A. Rzarch (Vienna 1891) which Terry acknowledges" . . . has not escaped criticism, especially on account of its numerous conjectural emendations, . . .", is logically consistent--If God throws down fire it should get hotter, right?--within the context of these lines. Bate's version, which relies heavily on the work of J. Geffcken (Leipzig 1902), is more in keeping with the text as a whole for further into Book V these lines appear:
"And a wind of winter then shall blow upon the earth, and the plain be filled with evil war again. For fire shall rain down from the heavenly plains on mortals, and there with blood, water, flash of lightning, murky darkness, night in heaven," (Terry)
"And then a wintry blast shall blow over the earth, and the plain shall be filled once more with evil war. For fire shall rain down from the floor of heaven upon men, and fire, water, thunderbolts, gloom, and murk in the sky." (Bate)
The association of cold weather with fire from heaven does not, of course, seem fantastic to a reader familiar with impact phenomena, but could not the text be recalling a particularly destructive episode of volcanism--Santorini perhaps? Fortunately the "Sibylline" is less allegorical than many ancient works--referring to a comet as a hairy or great star rather than only the divine name the comet had acquired. For instance, earlier in Book V one can read:
"But when the fourth year a great star shall shine, which alone shall the whole earth overpower because of honor, which was first assigned to lord Poseidon; then a great star shall come from heaven into the dreadful sea and burn the vastly deep, and Babylon itself, and the land of Italy," (Terry)
"But when after the fourth year a great star shines, which shall of itself destroy the whole earth . . . and from heaven a great star shall fall on the dread ocean and burn up the deep sea, with Babylon itself and the land of Italy," (Bate)
The mention of the fourth year could be significant in that objects, such as comet Encke, with an orbital period of 3.3X years must come to perihelion (where they would be most flamboyant) within the fourth year counted from their last close approach to the Sun. In fact there may have been an early Roman calendar which was based on these perihelion passages. Both Censorinus and Macrobius claimed that the year of Romulus (legendary founder of Rome) contained only 304 days which were divided into 10 months. As Clube and Napier (1982) point out, 4 of these years equal 1216 days or 3.33 solar years.
Also intriguing is the mention of Poseidon (generally depicted as the younger brother of Zeus) in these lines. This adds a new twist to his acknowledged attributes of earth shaker and stirrer of the deep.
Another strong indicator that the text is describing impact phenomena comes from these lines, also in Book V:
"And sometime high in the broad heaven above like thunder-roaring shall God's voice be heard. And the unwasting flames of the sun himself shall be no more, nor shall the brilliant light of the moon again be in the latest time, when God shall be the ruler. And dark gloom shall be o'er all the earth, and blinded men and evil beasts and woe; that day shall be a long time," (Terry)
"One day shall the voice of God be heard from above throughout the broad heaven as a peal of thunder. The rays of the very sun shall fail, the moon shall not give her bright light, in the time of the end, when God shall rule. There shall be thick darkness over all the earth: men shall be blind, and evil beasts also (?), and there shall be wailing, that day shall continue for a long time," (Bate)
It is very doubtful that any form of volcanic activity could cause wide-spread flash-blindness. Violently vaporizing space debris is known to be capable of producing this effect.
The Tunguska impact in 1908 ignited vegetation tens of kilometers away from the center of the blast; fortunately there were no people within this area of intense radiation. We can though, get an idea of the visual magnitude of this fall by way of a statement made by S.B. Semenov who witnessed the event from a trading post located about 100 km S.E. of the devastated area.
". . . I was sitting on my porch facing north when suddenly, to the northwest, there appeared a great flash of light. There was so much heat that I was no longer able to remain where I was--my shirt almost burned off my back. I saw a huge fireball that covered an enormous part of the sky. I only had a moment to note the size of it. Afterward it became dark and at the same time I felt an explosion that threw me several feet from the porch. I lost consciousness for a few moments and when I came to I heard a noise that shook the whole house and nearly moved it off its foundation." (J. Baxter and T. Atkins, The Fire Came By 1976)
Most likely, Mr. Semenov's perception that "it became dark" was subjective. It seemed dark to him as the blast wave hit because he had been watching the short duration fireball. When he regained consciousness the sky probably was darkened by debris reinforcing his impression, however prior to the atmospheric shock wave, Mr. Semenov was located between the morning sun and all the impact phenomena except the radiation component.
The Sibylline oracles are acknowledged to be of very ancient origin--they are mentioned by early classical Greek writers (Plato, Plutarch). Heraclitus of Ephesus, approximately 500 B.C., compares himself to a Sibyl--unfortunately the earliest extant copies are of fairly recent vintage (1545 A.D.). Having been through many hands they have, no doubt, been altered and embellished to suit the purpose of earlier users; however, these oracles seem to have retained a nexus of early observations (as do many so called apocalyptic works from various cultures) that may prove to be verifiable. Certainly, in light of recently acquired (reacquired?) knowledge, such literature should not be considered wholly fanciful or fictitious.