Fossilization

“ Especially needful is it to bear in mind that the cessation of one or more species at a certain line among the rocks of a particular district may mean nothing more than that, onward from the time marked by that line, these species, owing to some change in the conditions of life, were compelled to migrate or became locally extinct or, from some alteration in the conditions of fossilization, were no longer imbedded and preserved as fossils. ”

“ Or thirdly, the substance of the body has been converted into stone, but with such a delicate art, that it is in all respects, outwardly and inwardly, still the same body, with a new substance. We should observe, however, that these three different forms of fossilization, which we have successively described, are not always clearly distinct in actual fossil specimens, but are often curiously blended together according as the original organic substance has been more or less completely displaced, or the process of petrifaction has been more or less perfectly accomplished. ”

“ The older the rock, the simpler the plant and animal life it contains. Thus fossils can give a clue to the age of the rock strata.
Fossils can teach history. They tell us about plants and animals that are now extinct—the dinosaur, for example. They can also tell of ancient climates. Coral found in rocks in Greenland suggests it must have once been warm. Remains of fir and spruce trees have been found in the tropics.
How are fossils formed? Teeth, bone and wood don't last long in their original state. However, buried materials decompose, leaving a film of carbon as a fossil. ”

“ By a fossil is meant any body, or the traces of the existence of any body, whether animal or vegetable, which has been buried in the earth by natural causes. Now the remains of animals, especially of aquatic species, are found almost everywhere imbedded in stratified rocks, and sometimes, in the case of limestone, they are in such abundance as to constitute the entire mass of the rock itself. Shells and corals are the most frequent, and with them are often associated the bones and teeth of fishes, fragments of wood, impressions of leaves, and other organic substances. ”

“ Now we can easily see how the remains of organic bodies, growing at the time of the formation of these beds, should be preserved in a fossil form. Limestone rocks are thickly studded in places with all sorts of marine formations. Coal fields reveal wonders of early vegetative growth. From sandstone rocks, and shaly beds, we learn strange stories of animal life at the time they were forming. From a careful study of these remains together with the formation in which they occur, not only in one locality but all over the earth, geologists have gradually unfolded the history of life on the globe. ”

“ This aspect of the science is best seen in the historical and stratigraphical parts of geology, in which fossils are the chief data for study. The interpretation of a fossil into a species of organism, having its definite place in the elaborate classification of the zoölogist, or as an indicator of the time and place and mode of formation of the strata in which it is buried, is, to be sure, a most intricate and, at first thought it would seem, an unattractive process. ”

“ Thus, the same fossil, occurring in successive groups of strata, and with the merely trivial and varietal differences due to the gradual change in its environment, has been repeatedly described as a distinct species, with a distinct name, in every bed in which it was found. We know, however, that many fossils range vertically through many groups of strata, and there are some which even pass through several formations. The mere fact of a difference of physical position ought never to be taken into account at all in considering and determining the true affinities of a fossil. ”

“ FOSSILISATION.—The term "fossilisation" is applied to all those processes through which the remains of organised beings may pass in being converted into fossils. These processes are numerous and varied; but there are three principal modes of fossilisation which alone need be considered here. In the first instance, the fossil is to all intents and purposes an actual portion of the original organised being—such as a bone, a shell, or a piece of wood. ”

“ In the early part of the present century, and still more in the eighteenth century, the occurrence of fossil plants and animals in the earth’s crust formed the subject of animated, not to say acrimonious, discussion. The result was that many striking and ingenious theories were formulated as to the exact manner of formation of fossil remains, and the part played by the waters of the deluge in depositing fossiliferous strata. The earlier views on fossil vegetables are naturally bound up with the gradual evolution of geological science. ”

“ In many places these oldest stratified rock layers, bearing the fossils of the early marine life, both animal and vegetable, may be found directly on top of the older undifferentiated stone.
Fossils of this era yield algae, corallike plants, primitive Protozoa, and spongelike transition organisms. But the absence of such fossils in the early rock layers does not necessarily prove that living things were not elsewhere in existence at the time of their deposition. Life was sparse throughout these early times and only slowly made its way over the face of the earth. ”

“ The fleshy parts of animals do not petrify.
(3) Many animals among the invertebrates use mineral substances for protective or supporting structures. Small plants of various kinds follow a similar practice. These structures, being produced in stony materials, are readily converted into fossils. The shells of mollusks are the best known illustrations in this field, and all that is required for a shell to become a fossil is the extinction of the species of animal that produced it. Fossils of this type are extremely abundant. ”

“ The remarkable fossil remains and impressions of extinct animals and plants give us directly the historical evidence we need to understand the successive appearance and disappearance of the various species and groups. Geology has firmly established the chronological order of the sedimentary rocks, which have been successively formed of mud at the floor of the ocean, and has deduced their age from the thickness of the strata, and determined the relative date of their formation. The vast period during which organic life has been developing on the earth runs to many million years. ”

“ Since plants and animals changed through time and because their remains are found throughout the world, it is possible to erect a worldwide time scale based upon animal and plant evolution. In short, the fossils found in particular rock are characteristic representatives of the life at the time that rock originated and the fossils 6 found could have been entombed only at that time. One stratum, therefore, would have a total fossil assemblage quite different from the stratum above or below. ”

“ The succession of fossil remains throughout the whole geological series of rocks is the record of the change; and it became easy to see that the extreme slowness of these changes was such as to allow ample opportunity for the continuous automatic adjustment of the organic to the inorganic world, as well as of each organism to every other organism in the same area, by the simple processes of "variation and survival of the fittest." ”

“ The abnormal character of most of the fossiliferous deposits, the sudden world-wide change of climate they record, the marked degeneration in all organic forms in passing from the older to the modern world, together with the great outstanding fact that human beings, with thousands of other living species of animals and plants have at this great world-crisis left their fossils in the rocks all over the world, prove beyond a possible doubt that our once magnificently stocked world met with a tremendous catastrophe some thousands of years ago, before the dawn of history. ”

“ Go deeper still, and the kinds of animals change further. Fewer and fewer resemble those which now range the earth; more and more belong to other species.
Descend through layer after layer till we come to rocks built in earliest ages and not one fossil shall we find precisely the same as one animal living now.
So not only are the rocks built in successive order, stratum after stratum belonging to age after age in the past, but fossil-remains also are found in successive order, kind after kind belonging to past age after age. ”

“ Fossils as Guides to Age of Strata.—
In passing from fossil deposits of fairly recent origin to those of older date, we find the proportion of living species gradually diminish, being replaced by forms now extinct. After this the genera themselves are replaced by more ancient types, and if we penetrate still deeper into the series of geological strata, even families and orders of animals and plants give place to others entirely unknown at the present day. ”

“ Not only are the fossils invaluable to the Zoologist and Botanist, as representing the life of the past, but they are equally important to the Geologist, as we have just seen; his classification of the rocks is principally based on the extinct remains which they contain. The Primary, Secondary, and Tertiary Ages, with their characteristic fossils, according to many Geologists, were not confined to America, but extended all over the globe; the whole earth having passed at the same time successively through the Primary, Secondary, and Tertiary Ages. ”

“ The book was Charles Darwin's Origin of Species, the chapter that wonderful citation of the "Imperfections of the Geological Record." In this epoch-making chapter Darwin shows what conditions must prevail in any given place in order that fossils shall be formed, how unusual such conditions are, and how probable it is that fossils once imbedded in sediment of a sea-bed will be destroyed by metamorphosis of the rocks, or by denudation when the strata are raised above the water-level. ”

“ But no place has proved so favorable for fossil remains as the bed of the sea. The rapid deposit of sediment on the ocean floor and the remoteness from changes of heat and cold, have made the old ocean beds, such as we visited in our mountain of fossils, a wonderful storehouse of the life-forms of distant ages. The mollusks, corals, and crinoids furnish us the most varied and beautiful fossil remains, and in some cases the preservation is so perfect, that traces are retained of even the former colorings of the shells of mollusks and the scales of fishes that lived in the remotest times. ”

“ The theory of the origin of new species by variation will also explain why a species which has once died out never reappears, and why the fossil fauna and flora recede farther and farther from the living type in proportion as we trace it back to remoter ages. It would also account for the fact, that when we have to intercalate a new set of fossiliferous strata between two groups previously known, the newly discovered fossils serve to fill up gaps between specific or generic types previously familiar to us, supplying often the missing links of the chain, which, if transmutation is accepted, must once have been continuous. ”

“ How fossils tell of the geography of the past. Fossils are used not only as a record of the development of life upon the earth, but also in testimony to the physical geography of past epochs. They indicate whether in any region the climate was tropical, temperate, or arctic. Since species spread slowly from some center of dispersion where they originate until some barrier limits their migration farther, the occurrence of the same species in rocks of the same system in different countries implies the absence of such barriers at the period. ”

“ It is nevertheless remarkable, that on the continent of Europe, as in England, the fossil remains of mammalia belong almost exclusively to those of the Newer Pliocene and Post-Pliocene periods, and not to the Miocene or Eocene epochs, and when they are accompanied by land or river shells, these agree in great part, or entirely, with recent species. ”

“ The fossil remains of animals and plants wonderfully furnish the guidance which he needs. The corals and shells, the ferns and conifera, the teeth and bones found in the various strata of the earth-rind are the landmarks which point out to him his way through the labyrinth of the primitive ages of our globe, as the compass directs the mariner over the pathless sea. Every leading fossil has its fixed chronological character, and thus the age of the formation 6in which it occurs may be ascertained, and its place determined in the geological scale. ”

“ He discovered that the fossils in rocks, instead of being scattered haphazard, are arranged in regular systems, so that any given stratum of rock is labelled by its fossil population; that the order of succession of such groups of fossils is always the same in any vertical series of strata in which they occur, and The new geology that a fossil, having once disappeared, never reappears in a later stratum. ”

“ It is true that, later still, the old exploded errors about the plastic force and fermentation were from time to time revived, as they have been almost to the present day; but learned men, with few exceptions, no longer seriously questioned that fossils were real organisms, as the ancients had once believed. The many collections of fossils that had been brought together, and the illustrated works that had been published about them, were a foundation for greater progress, and, with the eighteenth century, the second period in the history of paleontology began. ”