| May, 1912 | |
| Per cent. of Volume | |
| Carbon dioxide | 55.4 |
| Carbon monoxide | 4.3 |
| Hydrogen | 7.7 |
| Nitrogen | 29.6 |
| Sulphurous acid | 2.9 |
| December, 1912 | |
| Per cent. of Weight | |
| Carbon dioxide | 42.9 |
| Nitrogen | 25.8 |
| Water | 27.5 |
| Sulphurous acid | 3.7 |
In the latter case, it has been shown that air had gained entrance to the volcanic gases, which air might have carried a quantity of water. But this quantity could not have been large judging by the amount of nitrogen present which corresponds to not quite 3 per cent. water by weight. In the former case water was not included in the analysis. At any event, a high percentage of water has frequently been observed in volcanic gases.
When the gases were left in contact with water a considerable part was absorbed thereby, particularly compounds of chlorine and fluorine and also ammonia and sulphurous acid. An analysis of such water showed 10 per cent. more fluorine than sulphurous acid and two fifths as much chlorine as fluorine. The ammonia amounted only to half of one per cent. of the chlorine. None of the rare air gases were present, which indicates that the nitrogen originated entirely from the magma and not from the air.
Brun has analyzed lavas from different volcanoes. The gases extracted therefrom naturally do not give as reliable information about the original atmosphere of the Earth as do the gases directly emanating from the volcanoes. As examples we quote the composition of the vapours in lavas ejected March 4, 1901, from Stromboli, and from Vesuvius in the well-known eruption of 1906. They show in percentages of volume:
| Stromboli | Vesuvius | |
| Free chlorine | 12.8 | 0 |
| Hydrate of chlorine | 2.0 | 6.6 |
| Sulphurous acid | 4.5 | 12.0 |
| Carbon dioxide | 60.2 | 73.8 |
| Carbon monoxide | 11.5 | traces |
| Hydrogen | 0.5 | 7.6 |
| Nitrogen | 6.9 | traces |
| Marsh-gas | 1.6 | 0 |
| 100.0 | 100.0 |
It will be noticed that the composition varies considerably. Free chlorine cannot very well be primigenial as it, like oxygen, combines with reducing substances. Chlorine may be produced by heating chloride of calcium with silica and ferro-silicates which are present in the magma. At all events, carbon dioxide constitutes the bulk. Next in importance are sulphurous acid and hydrate of chlorine. Carbon monoxide, hydrogen, and nitrogen may occur in quite considerable quantities but are sometimes almost wholly absent.
Day and Shepherd reached the conclusion that the gases emitted by the hot lava in the Halemaumau crater are nitrogen, water, carbon dioxide, carbon monoxide, sulphurous acid, hydrogen, sulphur vapour, also small quantities of chlorides, fluorides, and possibly ammonia. Such, at least approximately, should also the original composition of the Earth’s atmosphere have been when the crust was newly formed. Nitrogen, water, and carbon dioxide were the most important ingredients; in the high strata hydrogen was present. Oxygen was totally lacking and reducing gases such as hydrogen, sulphurous acid, and carbon monoxide abounded instead. If we further note the composition of comets and meteorites we find that cyanogen, carbohydrates, and carbon monoxide also are present in the former, argon and helium in the latter. It is therefore probable that these substances, although absent in the emanations from Kilauea, yet belonged to the primary atmospheres of the planets. The rare gases of the air especially should originally have come from the exterior parts of the sun, as did the nitrogen.
An atmosphere of such a composition would be utterly unendurable to living beings. It must, if organisms are going to thrive therein, be purified from such poisons as carbon dioxide, gaseous sulphur, cyanogen, and sulphurous acid. We know that such a process has taken place and that the sunlight has been the great chemist who produced oxygen and carbon from the carbon dioxide. The just mentioned poisonous gases were subsequently oxidized through electrical discharges. We all know that the plants up-build their framework under the influence of sunlight, consuming in the meantime carbon dioxide, water, and a little ammonia. In the process, oxygen is formed, as are also starch, cellulose, sugars, and albuminous substances with the aid of the green colouring matter in plants, chlorophyll, which considerably accelerates the action. Subsequently these new substances, which all (except the albuminous ones) belong to the carbohydrate group, are converted into principally carbon and water. The final result is that carbon dioxide through the agency of sunlight is split into its two constituents, carbon and oxygen. This process, which is comparatively rapid in the presence of chlorophyll, should also, although more slowly, take place without that medium; and in recent trials the chemists—particularly Daniel Berthelot—have, indeed succeeded in imitating without chlorophyll this important function of the plants through the application of light of a short wave length. In the course of the many millions of years which geology has proved necessary for the evolution of our planet, the carbon dioxide in the air was gradually converted into oxygen and carbon. As long as reducing gases, such as the poisonous ones mentioned, or any considerable quantities of carbohydrates and hydrogen yet remained in the atmosphere, the oxygen was consumed in their combustion. If a solid crust had not existed to prevent the oxygen from entering into the interior molten mass, it would also have found its way there and would have oxidized the reducing substances in the magma. The separation of the interior from the surrounding gas shell is therefore a necessary requisite for the existence of free oxygen in the air. Another condition is that the combustible gases escaping from the volcanoes must be added to the air at a sufficiently slow rate not to consume all of the simultaneously formed oxygen. A third requirement is that the liberated carbon should not in a renewed process of oxidation bind the oxygen just recovered. As long as the air still was reducing, this last condition was no doubt fulfilled for that very reason. At all events, the crust once formed and the original violent volcanic activity somewhat abated, the time finally arrived when free oxygen existed in the air. The previously present reducing gases were, except for small fractions, burned into water, carbon dioxide, and sulphuric acid and the nitrogen compounds had no doubt yielded free nitrogen to the stores of that gas already a part of the atmosphere. The time was now ripe for the first plants, probably low forms of algæ, which, in the oceans, commenced life on our planet. The carbon dioxide and hydrochloric acid of the air as well as the newly formed sulphuric acid were absorbed by the running water and caused a rapid disintegration producing silica and acid silicates. As plant life developed and extended the formation of oxygen increased. Falling vegetable matter was imbedded in slime which prevented the access of oxygen during decay and in this manner the fossil fuels were deposited. Koene of Brussels first pointed out that the carbon and the sulphuric compounds accumulated in the Earth would suffice to bind the oxygen of the air. Later investigations lead to the conclusion that the carbon alone is sufficient for the purpose. It would therefore appear that all the oxygen of the air is derived from carbon dioxide belonging to the original atmosphere or contributed thereto by the volcanoes.
The reason why carbon dioxide and water continuously are liberated from the magma is undoubtedly that the acid silicates are lighter than the basic and therefore accumulate in the exterior parts of the magma. A great surplus of silica exists there. Compounds containing water and carbon dioxide, i. e. hydrates and carbonates, are also light and should therefore congregate to the same strata where silica abounds, there partly to be dissolved by the free silica and thus setting water and carbonic acid free. The latter are, in contrast to silica, volatile and evaporate therefore into the air leaving the silica behind. This process is yet in evidence wherever the magma emerges as through the volcanoes. But also a few other acids in the magma are highly volatile, as sulphurous, thiosulphuric, and hydrochloric acids. These also belong to the volcanic gases, are dissolved by the water, and partake in the processes of disintegration. The carbon dioxide and hydrochloric acid form carbonates and chlorides. The former are extracted from the sea water by crustacea, sometimes also by plants, and form part of our sedimentary strata; the latter are soluble and remain in the water, chiefly as sodium chloride or common salt. The thiosulphuric acid, probably a product of ferrous sulphide and acids in the magma, has entered into numerous insoluble metallic sulphides found in the Earth. Partly, it has also been oxidized, like the sulphurous acid, into sulphuric acid and has then assisted in the processes of disintegration, forming gypsum which has been deposited in the sedimentary rocks.
The geologists believed formerly that the Earth gradually and continuously has grown cooler. This theory, however, struggled with the difficulty that certain cold time intervals, ice periods, were succeeded by warmer epochs. To begin with efforts were made to surmount this obstacle by assuming that an ice period on the north hemisphere was counterbalanced by a warm period on the south hemisphere and vice versa. In this manner, the mean temperature for the entire surface of the globe might possibly have been continuously decreasing although fluctuations had occurred on the two hemispheres. But this view has proved untenable, because the ice period has left traces also within the tropics, near the equator, as on Kilimanjaro, in New Guinea, and so on. It is now practically agreed that the last great ice period was characterized by a temperature between 4° to 5° C. (7° to 9° F.) below the present all over the surface of the Earth. This determination has been accomplished by measuring the difference in height between the terminals of the glaciers at present and the lowest points where their grinding action has left obvious traces. The ice coverings of North Europe, North-East America, South America, along the coast of Chile and in Argentina, as well as on the southern island of New Zealand, all appear to have existed simultaneously. Also during earlier eras, for instance during the Algonkian and the Permian epochs, ice periods have occurred. The latter, which was felt in Australia, India, and South Africa, is called the Gondwana-time. This period was formerly supposed not to have caused any temperature drop except in the tracts mentioned. Later investigations lead us to believe, as asserted by Holland in his presidential address to the geological section of the British Association at its 1914 meeting, that also this ice period simultaneously embraced the entire globe.