XII. GEOLOGY; ARCHAEOLOGY
ABYORMEN IS larger than the earth and has a smaller percentage of sea area even in the cold time, so the geologists had a great deal of territory to cover. They did not, of course, attempt to do it all; the basic plan was to attempt enough stratigraphic correlation to get a fair idea of its geological history and, if at all possible, find datable radio-actives in the series far enough down to get at least a minimum value for the age of the planet. The last was all the astronomers really wanted, but the biologists had considerably higher standards. They came along, prepared to analyze any fossils found by every technique known to their field.
Layer after layer of sedimentary rock was traced, sometimes for miles underground, sometimes only yards before it vanished — perhaps because quakes had shuffled it into a puzzle that took experience to solve, perhaps because the phenomena which had deposited it in the first place had covered only a limited area and the formation pinched out naturally. A limestone bed laid down over a million square miles at the bottom of a sea is one thing; a sandstone lens that was once the delta of a stream running into a small lake is something else — sometimes a rather inconvenient something else, when a problem of relative dates is in question.
Kruger thanked his luck that Commander Burke was not with this ground party and prayed constantly that he would not overhear any remarks made by the geologists, for Dar Lang Ahn was learning a good deal of English as time went on, and there are few places where a photographic memory can make itself more obvious or useful than in a stratigraphy problem. The geologists without exception regarded the native with awe and felt a friendship for him comparing strongly with Kruger’s own. Sooner or later the commander would learn; the boy hoped that by then his little friend’s popularity would have reached a point where the old officer would be moved to get rid of his suspicions.
Nowhere on the planet did there seem to be structures corresponding with the “shields” which characterize certain parts of Earth. Apparently all the present land surface had been submerged in the not too distant past; there was more than a suggestion that Abyormen suffered much more seismic and orogenic activity than Earth. One of the specialists suggested that a reason for this might lie in the “Long Year” seasonal changes, when the greater part of the sea water was deposited on the ice caps. A seismic check of the cap in the southern hemisphere (not over the south pole) indicated a thickness of nearly thirty-five thousand feet. It was snowing at the time the check was made, Theer never shone on this part of the planet, and Arren would not rise for several terrestrial years.
While several of Abyormen’s short years passed before any absolute dating of strata was possible, the astronomers learned what they had feared rather quickly. From the beginning, of course, the geologists had kept their eyes open for pegmatites and other igneous intrusions which might contain radioactives suitable for dating, and fairly soon these were found at several places on the continent they were examining. It was not possible to correlate these rocks with the sedimentaries, at the time, but one of them had a uranium-lead ratio corresponding to an age of just under one and a half billion years. It was a large sample, and ten independent checks were run, none varying more than about twenty million years from the mean. Since the astronomers were not willing to believe that Alcyone had been in existence longer than something like one per cent of that time they accepted the information a trifle glumly.
But dated or not, the sedimentaries had their own fields of interest. If Dar Lang Ahn had ever seen a fossil in his life he had never given it a second thought. This omission was easily remedied, for the sediments had their share of organic remains. A lens of limestone some two hundred miles across, near the center of the continent, seemed to consist largely of a reef deposit, and several hundred different species were found at various points within it. Shellfish that might have come straight from Earth were present by the thousands — at least, so it appeared to Kruger; a biologist spent much time pointing out technical differences.
“I suppose,” he finished, “that you could find a good many creatures virtually identical with these on the shores of your present oceans. There seems to be some ability in the mollusks and their relatives to ride out the changes of a planet. On Earth they’ve been around for half a billion years — changed, to be sure, but the basic plan seems to keep right on going.”
“I understand you in all but one point,” Dar Lang Ahn replied in his slow, careful English. “I have been with you all along here, and have seen fossils like this in many different layers of rock, as you say is reasonable, but I have never seen a living creature which in any way resembles those fossils.”
“Have you ever spent any length of time at the seashore?”
“Much. Nils Kruger and I walked along one for about three hundred miles recently, if the occasions in my previous eight hundred years don’t count.”
“That’s right!” Kruger exclaimed excitedly. “I knew there was something funny about that beach and never could put my finger on it. There weren’t any seashells, or stranded jellyfish, or anything of that nature. No wonder it looked queer!”
“Hmph. I confess that is distinctly odd. How about other sea creatures?”
“I don’t know. I think there are animals of various sorts living in the water, and I’m sure there are plants. I can’t think of very many different kinds, though.” The biologist gave this bit of information to those of his colleagues engaged in field work; he himself was too busy with fossil correlation to follow it up.
Gradually he established order out of the chaos. For purposes of discussion, he divided Abyormen’s past into periods whose boundaries in time seemed to have been established by the general flooding of this continent which had resulted in the limestone beds. The geologists could not find evidence for definite periods of mountain-building, which are usually better for such a purpose; on Abyormen, as they had already suspected, orogenic activity seemed to be fairly uniformly distributed through time.
There were, of course, many reasons why the world might be more active seismically than Earth. It was larger, for one thing — ninety-one hundred miles in diameter and forty per cent more massive, so that a one hundred seventy pound man weighed about one hundred eighty on its surface. The percentage difference was small, but the total tonnage of gravitational forces available for orogeny was much larger than on mankind’s home world. At any rate there was the evidence — mountain-building periods were short, frequent, and local.
This should have made the biology department happy, even though it promised trouble for the astronomers. Unfortunately the vertebrate fossils had produced another headache.
It had not proved difficult to set up a general sequence almost certainly corresponding to the course of evolution on the planet, spanning what must have been several hundred million years, if Earth could serve as an example. This sequence started with things just barely possessed of hard-enough interior parts to preserve, ran through bony creatures comparable to the fishes, and led eventually to legged creatures which quite obviously breathed air and spent their lives, or most of them, on dry land. It would have been nice to have been able to put the simple end of this series at the bottom of a page and Dar Lang Ahn at the top, with logically intermediate forms in between, but this was rendered impossible by the fact that every fossil vertebrate found that was possessed of bony limbs at all had six of them. Dar was sufficiently human to have two arms and two legs, with no visible trace of any others.
At the biologists’ urgent plea the native submitted to having a set of X-ray photographs made of himself. He was as interested as anyone in looking at the results, and was as able as any biologist to see that his skeleton bore no traces of a third pair of appendages.