Cenozoic

“ The Cenozoic age, the fourth and last volume of the great book, exhibits another advance in the development of animal life; and in the Tertiary the forerunners of the present mammals, and in the diluvial, man, appear. A similar process of development from lower to higher forms is shown in the vegetable world. ”

“ These shifted from broadly mesotrophic conditions in the earlier Cenozoic towards regionally partitioned oligotrophy and eutrophy as cooling climate increased localized upwelling [6] . Regional upwelling specifically increased in the Southern Ocean after the Eocene-Oligocene boundary, in equatorial open ocean systems, and in mid-latitude coastal upwelling systems, such as the Benguela and California systems, in the late Miocene. ”

“ Another suggestion is that new geological substrates were exposed linked to Late Cenozoic geomorphological changes ( [89] ) . However, if fires became more frequent and more severe as a result of a more predictable, intense dry season, then forests would be likely to retreat exposing new land surfaces for fynbos colonization.
[83] ) analyzed speciation in 11 Cape clades in relation to climate (aridity, seasonality) and geological substrate. They found that the upland flora on oligotrophic quartzites was ancient and generally associated with aseasonal mesic climates. ”

“ Total diversity shows Cenozoic increase but is sample size biased; conventional subsampling shows little net change. We calculate diversity from a separately compiled new diatom species range catalog, and recalculate Neptune subsampled-in-bin diversity using new methods to correct for increasing Cenozoic geographic endemism and decreasing Cenozoic evenness. We find coherent, substantial Cenozoic diversification in both datasets. Many living cold water species, including species important for export productivity, originate only in the latest Miocene or younger. ”

“ Abstract Modern flammable ecosystems include tropical and subtropical savannas, steppe grasslands, boreal forests, and temperate sclerophyll shrublands. Despite the apparent fiery nature of much contemporary vegetation, terrestrial fossil evidence would suggest we live in a time of low fire activity relative to the deep past. The inertinite content of coal, fossil charcoal, is strikingly low from the Eocene to the Pleistocene and no charcoalified mesofossils have been reported for the Cenozoic. ”

“ Here, during late Miocene and early Pliocene times, in the latter part of the Cenozoic era, a dryer and somewhat harsher climate had been accompanied by the appearance of wide plains fitted for grazing animals, as well as stretches of forest, with all varieties of landscape favoring great diversity as well as abundance of mammalian life. It was, perhaps, the golden age for most mammals, when food was plenty, climate not too severe, and every prospect pleased. ”

“ In the Laurentian Highlands the metamorphosed rocks are of pre-Cambrian age; in New England and the Appalachian region they are, in part at least, of Paleozoic age; and in the Sierra Nevada and Cascade Mountains metamorphosed Mesozoic and Cenozoic rocks occur. As movements in the outer portion of the earth's crust may produce fractures in any class of rocks, and as such fractures favour the intrusion of igneous material, the metamorphic rocks may contain igneous intrusions similar to those noted above in connection with sedimentary rocks. ”

“ The earth’s crust is believed to be at least 31⁄4 billion years old. In order to deal with this vast stretch of time, geologists have divided the billions of years into various time units and have given each unit a name. The great divisions of geologic time, called eras, are Early Precambrian, Late Precambrian, Paleozoic, Mesozoic, and Cenozoic. ”

“ By the close of the Tertiary the higher types of mammals had become marvelously differentiated into most of the present-day groups or types. A very significant feature of the evolution was the steady increase in relative size of brain. The vast numbers of fossil skeletons and bones of mammals found in Tertiary strata is scarcely believable. In our brief discussion we can do no more than describe a few representative examples of the Cenozoic evolution of mammals. ”

“ The lands in the Cenozoic began to bloom with more and more flowering plants and grand hardwood forests, the atmosphere is scented with sweet odours, a vast crowd of new kinds of insects appear, and the places of the once dominant reptiles of the lands and seas are taken by the mammals. Out of these struggles there rises a greater intelligence, seen in nearly all of the mammal stocks, but particularly in one, the monkey-ape-man. ”

“ The Triassic, Jurassic, and Cretaceous systems are grouped together as the Secondary or Mesozoic formations (Gr. mesos, intermediate; zoe, life) ; the organic remains of this "Middle-Life" period being, on the whole, intermediate in their characters between those of the palæozoic epoch and those of more modern strata. Lastly, the Eocene, Miocene, and Pliocene formations are grouped together as the Tertiary or Kainozoic rocks (Gr. kainos, new; zoe, life) ; because they constitute a "New-Life" period, in which the organic remains approximate in character to those now existing upon the globe. ”

“ 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. ”

“ When we examine a large area such as Europe, the average as well as the extreme height above the sea attained by the older formations is usually found to exceed that reached by the more modern ones, the primary or palaeozoic rising higher than the secondary, and these in their turn than the tertiary; while in reference to the three divisions of the tertiary, the lowest or Eocene group attains a higher summit-level than the Miocene, and these again a greater height than the Pliocene formations. ”

“ The three broad divisions—Palaeozoic, Mesozoic, Cainozoic—which are employed by geologists to mark three stages in the development of life on the earth, are based primarily upon the fossil contents of the strata which, at one time or another, have been continuously forming since the earliest times. ”

“ Between the Mesozoic and the next succeeding time which may be known as the Neozoic or Tertiary, [AG] there is in the arrangements of most geologists a great break in the succession of life; and undoubtedly the widespread and deep subsidence of the Cretaceous, followed by the elevation of land on a great scale at the beginning of the next period, is a physical cause sufficient to account for vast life changes. Yet we must not forget to consider that even in the Cretaceous itself there were new features beginning to appear. ”

“ Time has approved of this sagacious anticipation, and we can now maintain with serene confidence that the four great Eozoic periods—Laurentian, Labrador, Atlantic or Montalban, and Huronian—were all enlivened by the existence of both vegetable and animal life. And Eozoic life had its peculiar characteristics just as much as the Silurian or Carboniferous. This life has appeared in consonance with the general principles of evolution as announced by our most learned sages. ”

“ And the terms Palæozoic, Mesozoic, and Cainozoic, are used to indicate these three successive systems of life. It is true that some accept this belief with caution: knowing how geologic research has been all along tending to fill up what were once thought wide breaks. Sir Charles Lyell points out that "the hiatus which exists in Great Britain between the fossils of the Lias and those of the Magnesian Limestone, is supplied in Germany by the rich fauna and flora of the Muschelkalk, Keuper, and Bunter Sandstein, which we know to be of a date precisely intermediate." ”

“ By the study of the successive beds, more especially of those deposited in the times of continental submergence, we obtain a table of geological chronology which expresses the several stages of the formation of the earth’s crust, from that early time when a solid shell first formed on our nascent planet to the present day. By collecting the fossil remains embedded in the several layers and placing these in chronological order, we obtain in like manner histories of animal and plant life parallel to the physical changes indicated by the beds themselves. ”

“ The number of exotic forms which are common to the Eocene and Miocene strata of Europe, like those to be alluded to in the sequel which are common to the Eocene and Cretaceous fauna, demonstrate the remoteness of the times in which the geographical distribution of living plants originated. A great majority of the Eocene genera have disappeared from our temperate climates, but not the whole of them; and they must all have exerted some influence on the assemblages of species which succeeded them. ”

“ It is true that a great variety of evidence is afforded by the composition of the rocks, that glaciers have left their traces in glacial scratchings and transported boulders, also that proofs of arid or semiarid conditions are found in the reddish colour of rocks in certain portions of the Palaeozoic, Trias and Eocene; but fossils afford the most precise and conclusive evidence as to the past history of climate, because of the fact that adaptations to temperature have remained constant for millions of years. ”

“ The frequent occurrence of strata containing assemblages of organic forms which are intermediate between those of adjacent formations, is, to my mind, fatal to this view. In the well-known St. Cassian beds, for example, Palaeozoic and Mesozoic forms are commingled, and, between the Cretaceous and the Eocene formations, there are similar transitional beds. On the other hand, in the middle of the Silurian series, extensive unconformity of the strata indicates the lapse of vast intervals of time between the deposit of successive beds, without any corresponding change in the Fauna. ”

“ Ample proofs of these reiterated revolutions will be given in the sequel, and it will be seen that many distinct sets of sedimentary strata, each several hundreds or thousands of feet thick, are piled one upon the other in the earth's crust, each containing peculiar fossil animals and plants which are distinguishable with few exceptions from species now living. The mass of some of these strata consists almost entirely of corals, others are made up of shells, others of plants turned into coal, while some are without fossils. In one set of strata the species of fossils are marine ”

“ Paleozoic time, although shorter than the pre-Cambrian as measured by the thickness of the strata, must still be reckoned in millions of years. During this vast reach of time the changes in organisms were very great. It is according to the successive stages in the advance of life that the Paleozoic formations are arranged in five systems,—the Cambrian, the Ordovician, the Silurian, the Devonian, and the Carboniferous. ”

“ This underground circulation of mineral matter in a dissolved condition explains the occurrence of fossils in land areas which have not necessarily been submerged during any great length of time, for it is well known that plant and animal remains are not invariably washed into lakes or seas, and that all sedimentary deposits have not been built up in large bodies of water. Here we are dealing with what is known as the continental type of sedimentation and such fossils as dinosaurs, mastodons, three-toed horses, and other former inhabitants of land areas. ”

“ Some confusion has been introduced by the use of the term Cainozoic to include, on the one hand, the Tertiary period alone, and on the other hand, to make it include both the Tertiary and the post-Tertiary or Quaternary epochs; and in order that it may bear a relationship to the concepts of time and faunal development similar to those indicated by the terms Mesozoic and Palaeozoic it is advisable to restrict its use to the latter alternative. Thus the Cainozoic era would embrace all the geological periods from Eocene to Recent. ”

“ The main subdivisions of the stratified rocks are known by the following names:—
Page 44 Of these primary rock divisions, the Laurentian, Cambrian, Silurian, Devonian, Carboniferous, and Permian are collectively grouped together under the name of the Primary or Palœozoic rocks (Gr. palaios, ancient; zoe, life) . Not only do they constitute the oldest stratified accumulations, but from the extreme divergence between their animals and plants and those now in existence, they may appropriately be considered as belonging to an "Old-Life" period of the world's history. ”

“ Throughout are interspersed masses of current-bedded sand and occasional patches of iceborne clay.
The general absence from these beds of fossil remains may be ac- counted for by the conditions of deposit; they were formed in a strong current, which would be (except, perhaps, at the commencement and end of the period) unfavourable to the existence of animal life, while the remains of any plants or animals that may have come within its sweep would speedily be reduced by attrition, except of course those which were previously fossilized, and all of which are much rolled and waterworn. ”