The 800-lb flying probe rammed headlong into the comet at nearly 30,000 miles per hour and burrowed deep into the comet's nucleus. The crash released millions of pounds of subsurface material into space as a flyby spacecraft, in addition to Earth- and spaced-based telescopes, recorded the collision and its aftermath in detail (C&EN Online Latest News, Sept. 12, 2005).
Among the probes zooming in on the comet last year, NASA's Spitzer Space Telescope focused on infrared light emitted from fine dust particles that were ejected from the impact site. According to the research team-which was led by Carey M. Lisse of the Applied Physics Laboratory at Johns Hopkins University and includes 16 other scientists at the University of Maryland, College Park; California Institute of Technology; and elsewhere-analysis of the spectra reveals the IR signatures of a host of amorphous and crystalline inorganic powders. Included are minerals such as magnesium-rich forsterite and iron-rich fayalite (both in the olivine family); ferrosilite, an iron-rich pyroxene; and nontronite, a smectite clay containing iron, aluminum, and sodium. The spectra also feature telltale signs of other minerals, amorphous carbon, water ice, sulfides, and polyaromatic hydrocarbons.
The Drift marks probably the most awful convulsion and catastrophe that has ever fallen upon the globe. The ..deposit.. of these continental masses of clay, sand, and gravel was but one of the features of the apalling event. In addition to this the earth at the same time was cleft with great cracks or fissures, which reached down through many miles of the planet's crust to the central fires and released the boiling rocks imprisoned in its bosom, and these poured to the surface, as igneous, intrusive, or trap-rocks. Where the great breaks were not deep enough to reach the central fires, they left mighty fissures in the surface, which, in the Scandinavian regions, are known as fiords, and which constitute a striking feature of the scenery of these northern lands; they are great canals—hewn, as it were, in the rock—with high walls penetrating from the sea far into the interior of the land. They are found in Great Britain, Maine, Nova Scotia, Labrador, Greenland, and on the Western coast of North America.
David Dale Owen tells us that the outburst of traprock at the Dalles of the St. Croix came up through open fissures, breaking the continuity of strata, without tilting them into inclined planes." * It would appear as if the earth, in the first place, cracked into deep clefts, and the igneous matter within took advantage of these breaks to rise to the surface. It caught masses of the sandstone in its midst and hardened around them.
These great clefts seem to be, as Owen says, "lines radiating southwestwardly from Lake Superior, as if that was the seat of the disturbance which caused them." *Geological Survey of Wisconsin, Iowa, and Minnesota," p. 142.
Moreover, when we come to examine the face of the rocks on which the Drift came, we do not find them merely smoothed and ground down, as we might suppose a great, heavy mass of ice moving slowly over them would leave them.
There was something more than this. There was something, (whatever it was,) that fell upon them with awful force and literally smashed them, pounding, beating, pulverizing them, and turning one layer of mighty rock over upon another, and scattering them in the wildest confusion. We can not conceive of anything terrestrial that, let loose upon the bare rocks to-day, would or could produce such results.
Geikie says:"When the ' till' is removed from the underlying rocks, these almost invariably show either a well-smoothed, polished, and striated surface, or else a highly confused, broken, and smashed appearance."
Gratacap says:"' Crushed ledges' designate those plicated, overthrown, or curved exposures where parallel rocks, as talcose schist, usually vertical, are bent and fractured, as if by a maullike force, battering them from above. The strata are oftentimes tumbled over upon a cliff-side like a row of books, and rest upon heaps of fragments broken away by their exposed layers."
And when we pass from the underlying rocks to the "till" itself, we find the evidences of tremendous force exerted in the wildest and most tumultuous manner.
When the ..clay and stones.. were being deposited on those crushed and pounded rocks, they seem to have picked up the detritus of the earth in great masses, and whirled it wildly in among their own material, and deposited it in what are called "the intercalated beds."
It would seem as if cyclonic winds had been at work among the mass. While the "till" itself is devoid of fossils, "the intercalated beds" often contain them. Whatever was in or on the soil was seized upon, carried up into the air, then cast down, and mingled among the "till."
James Geikie says, speaking of these intercalated beds:
"They are twisted, bent, crumpled, and confused often in the wildest manner.
Layers of clay, sand, and gravel, which were probably deposited in a nearly horizontal plane, are puckered into folds and sharply curved into vertical positions. I have seen whole beds of sand and clay which had all the appearance of having been pushed forward bodily for some distance, the bedding assuming the most fantastic appearance. .
First, we are to find something that instantaneously increased to a vast extent the heat of our planet, vaporized the seas, and furnished material for deluges of rain, and great storms of snow, and accumulations of ice north and south of the equator and in the high mountains.
Secondly, we are to find something that, coming from above, smashed, pounded, and crushed "as with a maul," and rooted up as with a plow, the gigantic rocks of the surface, and scattered them for hundreds of miles from their original location.
Thirdly, we are to find something ..which brought to the planet.. vast, incalculable masses of clay and gravel, which did not contain any of the earth's fossils; which, like the witches of Macbeth,"Look not like th' inhabitants of earth,And yet are on it;" which are marked after a fashion which can not be found anywhere else on earth; produced in a laboratory which has not yet been discovered on the planet.
Fourthly, we are to find something that would produce cyclonic convulsions upon a scale for which the ordinary operations of nature furnish us no parallel.
Fifthly, we are to find some external force so mighty that it would crack the crust of the globe like an eggshell, lining its surface with great rents and seams, through which the molten interior boiled up to the light.
Would a comet meet all these prerequisites?
In the first place, it is, of course, impossible at this time to say precisely how the contact took place; whether the head of the comet fell into or approached close to the sun, like the comet of 1843, and then swung its mighty tail, hundreds of millions of miles in length, moving at a rate almost equal to the velocity of light, around through a great arc, and swept past the earth ;—the earth, as it were, going through the midst of the tail, which would extend for a vast distance beyond and around it. In this movement, the side of the earth, facing the advance of the tail, would receive and intercept the mass of material—stones, gravel, and the finely-ground-up-dust which, compacted by water, is now clay—which came in contact with it, while the comet would sail off into space, demoralized, perhaps, in its orbit, like Lexell's comet when it became entangled with Jupiter's moons, but shorn of a comparatively small portion of its substance.
Imagine such a creature as that, with a head fifty times as large as the moon, and a tail one hundred and sixteen million miles long, rushing past this poor little earth of ours, with its diameter of only seven thousand nine hundred and twenty-five miles! The earth, seven thousand nine hundred and twenty-five miles wide, would simply make a bullet-hole through that tail, fourteen million miles broad, where it passed through it !—a mere eyelethole—a pin-hole—closed up at once by the constant movements which take place in the tail of the comet. And yet in that moment of contact the side of the earth facing the comet might be covered with hundreds of feet of debris.
Or, on the other hand, the comet may, as described in some of the legends, have struck the earth, head on, amid-ships, and the shock may have changed the angle of inclination of the earth's axis, and thus have modified permanently the climate of our globe; and to this cause we might look also for the great cracks and breaks in the earth's surface, which constitute the fiords of the sea-coast and the trap-extrusions of the continents; and here, too,might be the cause of those mighty excavations, hundreds of feet deep, in which are now the Great Lakes of America, and from which, as we have seen, great cracks radiate out in all directions, like the fractures in a pane of glass where a stone has struck it.
The cavities in which rest the Great Lakes have been attributed to the ice-sheet, but it is difficult to comprehend how an ice-sheet could dig out and root out a hole, as in the case of Lake Superior, nine hundred feet deep!
(Ragnarok: the age of fire and gravel)
