Life's Dawn on Earth / Being the history of the oldest known fossil remains, and their relations to geological time and to the development of the animal kingdom

by Sir John William Dawson

Fig. 11. Portion of Eozoon magnified 100 diameters, showing the original Cell-wall with Tubulation, and the Supplemental Skeleton with Canals. (After Carpenter.)

(a.) Original tubulated wall or “Nummuline layer,” more magnified in fig. 2. (b, c.) “Intermediate skeleton,” with canals.

The immediate result was a composite paper in the Proceedings of the Geological Society, by Sir W. E. Logan, Dr. Carpenter, Dr. Hunt, and myself, in which the geology, palæontology, and mineralogy of Eozoon Canadense and its containing rocks were first given to the world.[L] It cannot be wondered at that when geologists and palæontologists were thus required to believe in the existence of organic remains in rocks regarded as altogether Azoic and hopelessly barren of fossils, and to carry back the dawn of life as far before those Primordial rocks, which were supposed to contain its first traces, as these are before the middle period of the earth’s life history, some hesitation should be felt. Further, the accurate appreciation of the evidence for such a fossil as Eozoon required an amount of knowledge of minerals, of the more humble types of animals, and of the conditions of mineralization of organic remains, possessed by few even of professional geologists. Thus Eozoon has met with some negative scepticism and a little positive opposition,—though the latter has been small in amount, when we consider the novel and startling character of the facts adduced.

[L] Journal Geological Society, February, 1865.

“The united thickness,” says Sir William Logan, “of these three great series, the Lower and Upper Laurentian and Huronian, may possibly far surpass that of all succeeding rocks, from the base of the Palæozoic to the present time. We are thus carried back to a period so far remote that the appearance of the so-called Primordial fauna may be considered a comparatively modern event.” So great a revolution of thought, and this based on one fossil, of a character little recognisable by geologists generally, might well tax the faith of a class of men usually regarded as somewhat faithless and sceptical. Yet this new extension of life has been generally received, and has found its way into text-books and popular treatises. Its opponents have been under the necessity of inventing the most strange and incredible pseudomorphoses of mineral substances to account for the facts; and evidently hold out rather in the spirit of adhesion to a lost cause than with any hope of ultimate success. As might have been expected, after the publication of the original paper, other facts developed themselves. Mr. Vennor found other and scarcely altered specimens in the Upper Laurentian or Huronian of Tudor. Gümbel recognised the organism in Laurentian Rocks in Bavaria and elsewhere in Europe, and discovered a new species in the Huronian of Bavaria.[M] Eozoon was recognised in Laurentian limestones in Massachusetts[N] and New York, and there has been a rapid growth of new facts increasing our knowledge of Foraminifera of similar types in the succeeding Palæozoic rocks. Special interest attaches to the discovery by Mr. Vennor of specimens of Eozoon contained in a dark micaceous limestone at Tudor, in Ontario, and really as little metamorphosed as many Silurian fossils. Though in this state they show their minute structures less perfectly than in the serpentine specimens, the fact is most important with reference to the vindication of the animal nature of Eozoon. Another fact whose significance is not to be over-estimated, is the recognition both by Dr. Carpenter and myself of specimens in which the canals are occupied by calcite like that of the organism itself. Quite recently I have, as mentioned in the last chapter, been enabled to re-examine the locality at Petite Nation originally discovered by Mr. Lowe, and am prepared to show that all the facts with reference to the mode of occurrence of the forms in the beds, and their association with layers of fragmental Eozoon, are strictly in accordance with the theory that these old Laurentian limestones are truly marine deposits, holding the remains of the sea animals of their time.

[M] Ueber das Vorkommen von Eozoon, 1866.

[N] By Mr. Bicknell at Newbury, and Mr. Burbank at Chelmsford. The latter gentleman has since maintained that the limestones at the latter place are not true beds; but his own descriptions and figures, lead to the belief that this is an error of observation on his part. The Eozoon in the Chelmsford specimens and in those of Warren, New York, is in small and rare fragments in serpentinous limestone.

Eozoon is not, however, the only witness to the great fact of Laurentian life, of which it is the most conspicuous exponent. In many of the Laurentian limestones, mixed with innumerable fragments of Eozoon, there are other fragments with traces of organic structure of a different character. There are also casts in silicious matter which seem to indicate smaller species of Foraminifera. There are besides to be summoned in evidence the enormous accumulations of carbon already referred to as existing in the Laurentian rocks, and the worm-burrows, of which very perfect traces exist in rocks probably of Upper Eozoic age.