Chapter II: The Beginning of Life on the Earth

The day must have been when the first living being appeared for the first time on our planet. Was it plant or animal? or a generalised organism uniting in some mysterious way the properties and powers of two kingdoms of nature, now so distinct, and even contrary to each other in their manifestations? Did it appear suddenly, or was it slowly evolved from dead matter by some process in which the albuminous or protoplasmic matter, which we know forms the basal substance of living beings, was first produced and then endowed with life? Did the first living being appear in a mature state, or was it merely a germ from which the mature individual could be produced? These are questions which science in its present state has no means of answering. We do not know any process by which the ingredients of protoplasm can be combined so as to produce that substance without a previous living being. We do not know what molecular differences may exist between dead albumen and that which we see growing and moving and instinct with life; still less do we know how to set up or establish these differences. We do not know the precise nature or relation to other forces of the energy which actuates living organisms. In our experience the simplest creatures that have life spring from previous germs, themselves the products of previous generations of living beings. Thus we are in the presence of great mysteries which it might be impossible for us to solve, even if we were permitted to visit some new planet on which the dawn of life was breaking.

Some things, however, we can infer as to the conditions of the introduction of life.

First, there is every reason to believe that the earth we inhabit was once a glowing, incandescent mass, condensing from a vaporous condition, and quite unfit for the abode of living beings, and which, even if in some previous state its materials had constituted the mass of an inhabited world, must have lost every trace of any living germ in the fervent heat to which it had been subjected. There must, therefore, have been in some way an absolute creation or origination of life and organisation.

Secondly, we may infer that in the earlier stages of the earth, when it was perhaps wholly or almost entirely covered with the waters, when it was still uniformly warmed with its own internal heat, when it was surrounded with a pall of dense vapours preventing radiation, and nursing its heat within itself, though in a condition entirely unsuited to the higher forms of life, it may have presented circumstances more favourable to the origination and multiplication of living beings of low organisation than at any subsequent time. This incubation of creative power in the vaporous mantle over the primA|val ocean was a favourite imagination of old thinkers, and is not obscurely hinted at in the Book of Genesis. It has been revived and much insisted on by evolutionists in our own time, though it has no certain foundation in scientific observation or experiment.

Thirdly, from the fact that plant-life alone has the power of subsisting on inorganic matter, and that plants furnish all the nourishment of animals, we may fairly infer that the life of the plant preceded that of the animal. It has, indeed, been suggested that some of the humbler forms of life may combine in a rude and simple way enough of the powers of the plant and the animal to enable them to bridge over the double gap between the animal and the plant, and the animal and the mineral, or that such creatures may in their early stages carry on vegetable functions, and in their later those of the animal. It is theoretically possible that life may have begun with such creatures, which some of the results of microscopical research would lead us to believe still exist. It is, however, on the whole more probable that simple plants first existed, and furnished pabulum to animals of low grade introduced almost contemporaneously.

Fourthly, all our knowledge of the succession of life leads us to believe that it was not the higher plants and animals that first sprang into existence from the teeming earth, but creatures of low and humble organisation, suited to the then immature and unfinished condition of the planet. It is also in accordance with the amazing fecundity of the seas in all geological periods in these lower forms of life, to suppose that the earliest living things originated in the waters, and that the plants and animals of the land are of later date.

Do we know anything from actual observation of this earliest population of the world? Such knowledge we can hope to acquire only by studying the oldest formations known to us; and these, it must be confessed, exist in a state so highly crystalline, and so much affected by internal heat, by mechanical pressure, and by movement, as to render it little likely that organic remains should be preserved in them in a state fit for recognition.

In many parts of the world, and notably in Canada and Scandinavia, as well as in Wales, Scotland, and Bavaria, the older PalA|ozoic rocks, the lowest containing plants in great abundance, rest on still older crystalline beds, which have become hard and crystalline in pre-PalA|ozoic times, and have contributed sand and pebbles to the succeeding very ancient deposits. These old rocksaEuro"the Eozoic series of our tableaEuro"may be grouped in two great systems, the Laurentian and Huronian (Fig. 14). The former may be conveniently divided into three members: First, the Bojian, or Ottawa gneiss, consisting of stratified granite rocks, usually of a red colour, and of very great thickness. This contains, so far as known, no limestone, and has afforded as yet no trace of fossils. Secondly, the Middle Laurentian, the greater part of which consists of gneiss, but containing important beds of other rocks, as quartzite, iron ore, and limestone. It is in this series that we have the first evidence of life, and it is here also that we find the greatest abundance of carbon, in the form of graphite or plumbago, and also large quantities of calcium phosphate, or bone earth. Thirdly, the Upper Laurentian or Norian series. This consists in great part of Labadorite, or lime feldspar, but has also beds of ordinary gneiss, limestone, and iron ore.

_a_, Lower Laurentian.
_b_, Middle Laurentian.
_c_, Upper Laurentian.
_d_, Huronian.
_e_, Cambrian and Silurian.]

The latter, the Huronian, is much less crystalline, and is divisible into two seriesaEuro"the Lower Huronian, which includes many beds of volcanic origin, and the Upper Huronian, which has afforded some obscure fossils. The Huronian was first recognised by Sir W. E. Logan in Canada, but corresponding rocks exist in Europe. The Pebidian series of Hicks in Wales is probably of this age.

It is likely that much of the present appearance and condition of the most ancient rocks may be attributed to metamorphism, that is, to the slow baking under the influence of heat, heated water, and pressure, to which they have been subjected in the lower parts of the earthaEuro(TM)s crust, when buried deeply under newer deposits. It is also true, however, as Dr. Sterry Hunt has pointed out in detail, that they present mineral characters which show a mode of deposition different from that which has prevailed subsequently, and probably indicating great ejections of heated mineral matter into the primitive ocean, and comparatively little of that deposit therein of mere sand and clay which has prevailed in subsequent geological periods. In short, these rocks have an unmistakably primitive aspect, distinguishing them from those of later times, and conveying the impression that they approach at least to the records of that time when a heated ocean first rested on the thin and recently solidified crust of our planet. If this is really the case, then our Lower LaurentianaEuro"hard, compact, destitute of limestone, and composed of material which may be little else than the _dA(C)bris_ of products of internal heat merely spread out into bedded forms by wateraEuro"may represent a time when no living thing as yet tenanted the waters; and the dawn of life may have appeared in that period when the Middle Laurentian beds were laid down. Here at least we find two kinds of evidence pointing to the existence of certain forms of life in the waters.

The first depends on the mineral character of the beds themselves. This formation holds several very thick beds of limestone. Now although this kind of rock may, under certain circumstances, be deposited directly from solution in water, it is not ordinarily so deposited, but more usually through the agency of living beings inhabiting the waters, and forming their skeletons or hard parts of limestone derived from the water, usually through the medium of humble forms of plant life. In this way are formed reefs of coral and beds of shells and of chalky ooze, all composed of material once constituting the skeletons of animals. The study of limestones of all geological ages shows that this has been the usual mode of their formation. If the Laurentian limestones had a similar origin, the seas of that period must have swarmed with animals having calcareous coverings; and the study of more modern limestones which have become highly crystalline shows that it is quite possible that the forms and structures of these organisms may have been obliterated.

Again, the Middle Laurentian abounds in carbon or coaly matter. True, this is in the form of graphite or plumbago, but this condition may be a result of metamorphism; and we know that the carbon of coal-beds and bituminous shales of much more modern times has been altered into graphite. Further, the graphite occurs in the way in which we should expect it to occur if of organic origin. It is found disseminated in the limestone, just as bituminous matter is found in unaltered rocks of this kind. It is found interlaminated with gneiss, as carbonaceous and bituminous matters are found in the shales of the ordinary fossiliferous rocks, where these substances are known to be of organic origin. The graphite also occurs in a very pure form in irregular veins, just as in some bituminous formations the rock oil, oozing into fissures, has been hardened into asphalt or coaly matter.[3]

To these facts may be added the presence of thick beds and veins of iron ore and of apatite or calcium phosphate (bone earth). Both of these substances occur in a disseminated state in nearly all rocks, but they are concentrated into definite deposits by the action of life. Iron is usually dissolved out and redeposited by acids produced in the decay of vegetable matter, as we see in the clay ironstones of the coal formation and in bog-iron ores. Calcic phosphate is taken up by many animals, and forms their shells or skeletons, and on their death is deposited in beds on the sea-bottom, sometimes to a very considerable extent.

The concurrence of all these phenomena in the Middle Laurentian may be held to afford a strong presumption that, could we discover these rocks in an unaltered state, we should find the limestones filled with marine fossils and the graphite showing the forms or structure of plants. The only startling feature in this conclusion is, that if we admit it, we must also admit that life was developed in the Laurentian time in an exuberance not surpassed, if equalled, in any subsequent period. Still, there is nothing incredible in this, for if the forms of life were few and low, their increase may have been rapid, because unchecked; and they no doubt found in the ancient seas a surplusage of material on which to feed and with which to construct their skeletons. Dr. Hunt has estimated that the amount of carbon now sealed up as coaly matter would, if diffused in the atmosphere as carbon dioxide, afford 600 times the quantity of that gas at present floating in the air. A still more vast amount is sealed up in the limestone of the several geological formations. The same chemist has shown that the quantity of lime held in solution in the ocean must have been much greater in Laurentian times than at present. These facts at least allow us to suppose that in the Eozoic times there were great supplies of carbon and of lime available to such creatures of low organisation as were capable of profiting by them; and we have no reason to doubt that there may have been plants and animals so constituted as to flourish in conditions of this kind, in which perhaps scarcely any modern species could exist.

These probabilities have caused geologists anxiously to search for any traces of fossil organic remains in the old Laurentian rocks; and they have been rewarded by the discovery of one species, _Eozoon Canadense_, still often referred to as only a problematical fossil; but this arises to a large extent from the prevalent want of knowledge sufficient to appreciate the evidence for its organic character. This being once admitted, we have in the existence of _Eozoon_ alone a sufficient cause for the accumulation of much of the Laurentian limestone, though there is reason to believe that it was not the only inhabitant of those ancient seas.

1, Natural size; showing general form, and acervuline portion above and laminated portion below. 2, Enlarged casts of cells from upper part. 3, Enlarged casts of cells from the lower part of the acervuline portion. 4, Enlarged casts of sarcode layers from the laminated part.]

The best specimens of _Eozoon_ occur as rounded, flattened, or more or less irregular lumps or masses in certain layers of the Laurentian limestone. When weathered on the surface of the rock, these lumps show a regular concentric lamination, caused by thin fibres of limestone, alternating with other mineral substances, filling up the spaces between them. When these intervening layers are composed of such minerals as Serpentine, Loganite, Pyroxene, or Dolomite, which are more resisting than the limestone, they project when weathered, or when the limestone is etched by an acid, so as to show the lamination very distinctly. At the lower surface of the masses the layers are seen to be thicker than they are above, and in perfect specimens they are seen toward the surface to break up into small rounded vesicles of calcite, like little bubbles, which constitute the so-called acervuline condition of _Eozoon_ (Fig. 15, No. 2). Slices of the fossil etched with an acid show these appearances very perfectly, and can even be printed from, so as to present perfect nature-prints of the structure (Fig. 16).

FIG. 16.aEuro"Nature-printed specimen of _Eozoon_ slightly etched with acid. It shows the lamination, and at one side fragmental _Eozoon_ (_LifeaEuro(TM)s Dawn on Earth_).

On etching a small fragment or slice with very dilute acid, so as to dissolve away the calcite slowly, if the specimen be well preserved, we find that the calcite layers have a very curious structure. This is indicated by the appearance of little white or transparent threads of Serpentine, Dolomite, or Pyroxene, which ramify throughout the substance of the limestone layers, and are left intact when they have been dissolved. These little processes must originally have been pores in the limestone layers, which have been filled with the substance which constitutes the alternate laminA|. In addition to this, if we use a somewhat high microscopic power, and especially if we study the structures as seen in thin transparent slices, we can perceive a still finer tubulation along the sides of the calcite layers, represented by extremely minute parallel rods of mineral matter (Figs. 17, 18).

Now if we regard these structures as those of an infiltrated fossil, as described in last chapter, their interpretation will not be difficult. The original organism was composed of calcareous matter in thin concentric laminA|, connected with each other by pillars and plates of similar material. Between these laminA| was lodged the soft, jelly-like substance of a marine animal, growing by the addition of successive layers, each protected by a thin calcareous crust. The layers were originally traversed by very numerous parallel tubuli, permitting the soft protoplasm to penetrate them; and when, in the progress of growth, it was necessary to strengthen these layers, they were thickened by a supplemental deposit traversed by larger and ramifying canals. When the animal was dead, and its soft parts removed by decay, the chambers between the laminA|, as well as the minute canals and tubuli, became infiltrated with mineral matter, in the manner described in the last chapter, and when so preserved became absolutely imperishable under any circumstances short of absolute fusion.

Taken from the specimen in which they were first recognised (_LifeaEuro(TM)s Dawn on Earth_).]

_a_, Original tubulated wall or aEurooeNummuline layer.aEuroŁ More magnified in Fig. A. _b_, _c_, Intermediate skeleton, with canals.]

This interpretation leads to the conclusion, at which I arrived from the study of the first well-preserved specimen ever submitted to microscopic examination, that the animal which produced the calcareous skeleton of _Eozoon_ was a member of that lowest grade of Protozoa known as Foraminifera; and which, after living through the whole of geological time, still abound in the sea. The main differences are, that _Eozoon_ presents a somewhat generalised structure, intermediate between two modern types, and that it attained to a gigantic size compared with most of these organisms in later periods. How near it approaches in structure to some modern forms may be seen by comparison of the recent species represented in Fig. 19, in which the parts corresponding to the chambers, laminA|, tubuli, and canals of _Eozoon_ can be readily distinguished.

_a_, Cells.
_b_, Original cell-wall with tubuli.
_c_, Supplementary skeleton with canals.]

The modern animals of this group are wholly composed of soft gelatinous protoplasm or sarcode, the outer layer of which is usually somewhat denser than the inner portion; but both are structureless, except that the inner layer may present a more or less distinct granular appearance. Many of them show a distinct spot or cell, called the nucleus, and some have minute transparent vesicles, which contract and expand alternately, and appear to be of the nature of circulatory or excretory organs. They have no proper alimentary canal, but receive their food into the general mass and digest it in temporary cavities. Their means of locomotion and prehension are soft thread-like or finger-like processes, extended at will from the surface of any part of the body, and known as false feet (pseudopodia). From these processes the whole group has obtained the name of Rhizopods, or rootfooted animals. They may be regarded as constituting the simplest and humblest form of animal life certainly known to us.

The very numerous species of these creatures existing in the waters of the modern world may be arranged under three principal groups. The first and highest includes those which have lobate or finger-like pseudopods, and a well-developed nucleus and pulsating vesicle (Fig. 20, _a_). They are mostly inhabitants of fresh water, and destitute of a hard crust or shell. A second group, including many inhabitants of the sea as well as of fresh waters, has thread-like radiating pseudopodia[4] (Fig. 20 _b_). Some of these form beautiful silicious skeletons. A third group, essentially marine, consists of those with reticulated pseudopodia, and usually destitute of distinct nucleus and pulsating vesicle (Fig. 21). They produce beautiful calcareous skeletons, often very complex, or sometimes are content to cover themselves with a crust of agglutinated grains of sand. It is to this last group that _Eozoon_ belongs, and to the highest division of itaEuro"that which has the shell perforated with minute pores, often of two kinds. It is curious that just as we have the chambers and pores of _Eozoon_ filled with serpentine, so in all geological formations and in the modern seas it is not uncommon to find Foraminifera having their cavities filled with glauconite and other hydrous silicates allied to serpentine.

If we attempt to trace the Rhizopods onward from the Middle Laurentian, we are met with a great hiatus in the Upper Laurentian. The species _Eozoon Bavaricum_ has, however, been found in rocks apparently of Huronian age; but this is the last known appearance of _Eozoon_, properly so-called. In the Cambrian or Siluro-Cambrian, however, we meet with many gigantic Protozoa, more especially those known as _Stromatopora_, _ArchA|ocyathus_, _Receptaculites_, and _Cryptozoon_.

_a_, Section of the same, magnified.
_b_, Small portion highly magnified, showing laminA| and pillars.]

The typical StromatoporA|, or Layer-corals, consist, like _Eozoon_, of concentric layers, connected by numerous pillars, which are often, though not always, more definite and regular than in the Laurentian fossil. The laminA| are perforated, but more coarsely than in _Eozoon_, and they are often thickened with supplemental deposit which, in some of the forms, presents canals radiating from vertical tubes or bundles of tubes penetrating the mass (Figs. 22, 23). The mode of growth of _Stromatopora_ must have closely resembled that of _Eozoon_, and the forms produced are so similar that it is often quite impossible to distinguish them by the naked eye. Like _Eozoon_, they form the substance of important limestones, and single masses are sometimes found as much as three feet in diameter. The StromatoporA| extend from the Upper Cambrian to the Devonian inclusive. In the Carboniferous they are continued by smaller and more regular organisms of the genus _Loftusia_,[5] and this genus seems to extend without marked change up to the Eocene Tertiary. Recent students of the StromatoporA| seem disposed to promote them from the province of Protozoa to that of the Hydroids.[6] The reasons for this seem cogent in the case of some of the forms, but in my judgment fail in others, more especially in the older forms. It may ultimately be found that the group as now held includes very different types of structure. In modern times I know of no nearer representative than the animal whose skeleton often adheres in red encrusting patches to our specimens of corals, and which is known as _Polytrema_. In general structure it is not very far from being a very degenerate kind of _Stromatopora_.

It is curious that in the line of succession above stated, the beautiful tubulated cell-wall of _Eozoon_ disappears; and this structure seems, after the Laurentian, to be for ever divorced from the great laminated Protozoans. It reappears in the Carboniferous, in certain smaller organisms of the type of the _Nummulites_, or Money-stone Foraminifers, and is continued in this group of smaller and free animals down to the present time. In the Cretaceous and early Tertiary periods, the Foraminifera of different types have been nearly as great rock-builders as they were in the Laurentian. Some of these later rock-builders, however, have belonged to the lower or imperforate group; others to the higher or Rotaline and Nummuline groups; and, as a whole, they have been individually small, making up in numbers what they lacked in size. Probably the conditions for enabling animals of this type rapidly, and on a large scale, to collect calcareous matter, were more favourable in the Laurentian than they have ever been since.

_a_, Pores of the inner wall.]

In the Siluro-Cambrian age two other forms of gigantic Foraminiferal Protozoans were introduced, widely different from _Eozoon_, and destined apparently not to survive the period in which they appeared. These were _ArchA|ocyathus_, the ancient Cup-corals, and Receptaculites, which may perhaps be called the Sack-corals. Both are quite remote from _Eozoon_ in structure, wanting its complexity in the matter of minute tubules, and having greater regularity and complication on the large scale. _ArchA|ocyathus_ had the form of a hollow inverted cone with double perforated walls, connected by radiating irregular plates, also perforated (Fig. 24). It has been regarded as a sponge, and some species are certainly accompanied with spicules; but these I have ascertained to be merely accidental, and will be referred to in the next chapter. The true structure of _ArchA|ocyathus_ consists of radiating calcareous plates enclosing chambers connected by pores. ArchA|ocyathus came in with the Later Cambrian, and seems to have died out in the Siluro-Cambrian. The only more modern things which at all resemble it are the Foraminifera called _Dactylopora_, which belong to the Tertiary period.

_a_, Aperture.
_b_, Inner wall.
_c_, Outer wall.
_n_, Nucleus, or primary chamber.
_v_, Internal cavity.]

Receptaculites is a still more complex organism. It has a sack-like form, often attaining a large size, and the double walls are composed of square or rhombic plates, connected with each other by hollow tubes from which proceed canals perforating the plates (Fig. 25). This curious structure is confined to the Siluro-Cambrian, and is so dissimilar from modern forms that its affinities have been subject to grave doubts.

We thus have presented to us the remarkable fact that in the PalA|ozoic age we have no precise representative of _Eozoon_, but instead three divergent types, differing from it and from each other, all apparently specialised to particular uses, all temporary in their duration; while in later times nature seems to have returned nearer to the type of _Eozoon_, though on a smaller scale, and separating some characters conjoined in it. Some portion of this curious result may be due to our ignorance; and it would be interesting to know, what we may know some day, how this type of life was represented in the long interval between the Huronian and the Upper Cambrian, when perhaps there may have been forms that would at least enable us to connect _Eozoon_ and _Stromatopora_.

Another link in the chain of being remains to be noticed here. In the Laurentian limestones we meet with numerous minute spherical bodies and groups of spheres with calcareous tubulated tests.[7] These may either be small ForaminiferA|, distinct from _Eozoon_, or may be germs or detached cells from its surface. Similar bodies are found in the lower part of the Siluro-Cambrian, in the Quebec group at Point Levis; and there they are filled with a species of glauconite constituting a sort of greensand rock. Still higher, in the Carboniferous, there are very numerous species of Foraminifera, presenting forms very similar to those in the modern seas, so that in the smaller shells of this group we seem to have evidence of a continuous series all the way from the Laurentian to the present time. The greater laminated forms co-exist with these up to the Eocene Tertiary. Throughout the whole of geological timeaEuro"from the formation of the Laurentian limestones to that of the chalky ooze accumulating in the modern oceanaEuro"these humble creatures have been among the chief instruments in seizing on the calcareous matter of the waters and depositing it in the form of limestone.

_a_, _Nummulites lA|vigata_aEuro"Eocene. _b_, The same, showing chambered interior. _c_, Milioline limestone, magnifiedaEuro"Eocene, Paris. _d_, Hard Chalk, section magnifiedaEuro"Cretaceous.]

I have said nothing of the development of higher forms of animal life from _Eozoon_, simply because I know nothing of it. We shall see in the next chapter that these are introduced seemingly in an independent manner. We may be content to trace foraminiferal life along its own line of development, waxing and waning, but ever confined within the same general boundaries, from the Laurentian to the present time. It is likely that if, in any of the ages constituting this vast lapse of time, a dredge had been dropped into the depths of ocean, it would have brought up Foraminifera not essentially different in form and structure. If any one asks to what extent the successive species constituting this almost endless chain may be descendants one of the other, we have no absolutely certain information to give. On the one hand, it is not inconceivable that such forms as _Stromatopora_ or _Nummulina_ may have descended from _Eozoon_. On the other hand, it is equally conceivable that the same power which produced _Eozoon_ at first, whether from dead matter or from some unknown lower form of life, may have repeated the process in later times with modifications. In any case it is probable that the Foraminifera have experienced alternations of expansion and shrinkage, of elevation and decadence, in the lapse of geological time. There were times in which many new forms swarmed into existence, and times in which old forms were becoming extinct without being replaced by others. In so far as the areas of the continents and the adjacent waters are concerned, those periods when the land was subsiding under the ocean must have been their times of prosperity, those in which the crust of the earth shrunk and raised up large areas of land must have been their times of decay. Still this lowest form of animal life has never perished, but has always found abundant place for itself, however pressed by physical change and by the introduction of higher beings.

1/6th Nat. Size.]