The Old Age And Death Of The Earth

( Originally Published 1915 )

WE have studied the "life" of the Earth : we have pictured its birth and development and have learned something of the continual circulation taking place upon its surface, the electric currents which traverse its mass, and the tremors and shocks to which it is subjected. Finally, we have considered the action of destructive agents upon the land surface and the compensatory influences at work, analogous to those which defend a living being against the attacks of germs of disease. But a healthy being, even if it success-fully resist the efforts of morbid action, must finally arrive at a state of old age. With age the natural forces diminish, the circulation slackens and death ensues, an accompaniment of the cold that succeeds the warmth of life.

In these final pages we shall endeavour to find out if the Earth forms any exception to this law, or whether, on the contrary, it also grows old and in due course dies.

In the first place, what is the degree of permanence of the actual present state of the terrestrial globe?

The conflict between the land-surface and the exterior agencies, the latter tending to wear it away and the former striving to defend itself, will endure for a long time yet. The waters will have for many ages to continue their attack against the solid material brought to the surface of the Earth by the play of interior forces, and the changes brought about in the relative position of pre-existing masses by seismic disturbances.

The atmosphere during this time, or at least for some time, will grow richer in carbonic acid. On the one hand, volcanoes, the activity of which seems to be actually increasing and whose manifestations will augment in number in proportion to the foldings of the crust, producing new fissures, set free an abundance of this gas. On the other hand, the immense progress of industry, by utilising to exhaustion the mineral fuel contained in the depths of the Earth's crust, tends to increase the proportion of carbonic acid in the atmosphere.

For some time, perhaps a very long one, this proportion will augment. Accordingly the influence that this gas exerts as regards the conservation of heat will also increase, and this will protect the Earth against a too rapid cooling. Some idea of this will be obtained by considering that if the carbonic acid actually contained in the atmosphere viz : 1/3000 part of the atmosphere, were removed, the temperature of the Earth's surface would diminish by 2° C. [36° F.], and this diminution would greatly accentuate the present climatic inequalities of the various regions of the Earth. If, on the contrary, the proportion of carbonic acid were to increase, for example, if its volume became double, we should experience a gain of 4° C. [7.2° F.], in temperature, and 8° C. [14.4° F.], if it became quadruple. Furthermore, not only would the mean temperature rise, but there would also be an accompanying tendency to climatic equalisation.

The study of the Earth's past has shown us that variations of this kind formerly occurred, and had an influence upon the phenomena of animal and vegetable life, the importance of which is shown by geology. If the carbonic acid in-creases, which is shown by the continued absorption by the water of the oceans, above which the proportion of this gas in the atmosphere is one-tenth less than above the land-surface, these conditions of climatic amelioration would be realised, and the following period would be a temperate epoch, in the course of which there would be no occasion to dread the recurrence of those terrible glacial periods which characterised the beginning of the Quaternary era. The soil would, thus, increase in fertility, for the rise in temperature of the air above it would increase the quantity of water-vapour contained in the atmosphere, and equally, therefore, the abundance of aqueous precipitation. Consequently, there would ensue a richer vegetation and better crops for the use of mankind living in these favoured times.

This, however will only be a temporary alleviation of the Earth's passage towards old age and death. At the end of a considerable number of centuries, estimated by Helmholtz at 17,000,000 years,' the Sun will be reduced in size to a quarter of its actual volume on account of the loss of heat due to its continued radiation, and a long time before this has taken place the temperature of the Earth will not exceed zero C. [32 F.]. Life will thus not last for the whole of this period the great German physicist judged its ultimate duration to be about 6,000,000 years.

What will then happen to the Earth itself after life has ceased to be on its surface? Will Man, by utilising the forces of Nature and the future discoveries of science that will continue to be made, have been able to make use of extra-terrestrial forces and so postpone this state of affairs, or even to betake himself to other and newer worlds?

In the process of the gradual cooling of the Sun and the consequent fall of the terrestrial temperature, the successive stages of the Earth's state after the disappearance of life from its surface will be as follows. The oceans and rivers, will first become transformed into masses of ice, and the clouds having condensed into snow and precipitated on the ground, will no longer afford the Earth the protection they formerly did against loss of heat by radiation into space. From this time, therefore, the temperature will fall with greater rapidity.

Carbonic acid will disappear in its turn; when the temperature is sufficiently low it will fall to the ground in the solid form as a fine snow-like substance, which is nowadays employed in the laboratory to produce cold. This condensation will remove the last defence of the Earth against radiation, and so the rate of cooling from that time on will still further accelerate. When the temperature reaches 730 C. absolute [2o° C. below the ordinary thermometric zero (328° F.)], new oceans will come into being, and will accumulate in the hollows of the ice which covers the planet. These new oceans will be produced by the liquefaction of nitrogen and oxygen and the remaining atmosphere will consist only of hydrogen and helium, and will be in a state of extreme tenuity. The cold crust will thus cover a globe exteriorly inert, but the interior will continue to remain as magma in an incandescent state for thousands of centuries. A very small portion only of this heat will come to the surface, con-ducted through the crust, which gets thicker and thicker, and the temperature will only be maintained above absolute zero [ – 273° C. or – 459.4° F.] by the radiations received from the cooling sun, which after attaining a dull red condition will also finally become dark.

Then the Sun will enter on its final period, a superficial crust being formed by solidification, just as occurred in the case of the Earth at the beginning of its history. At first it will be a very thin skin, constantly broken and fissured by the force of the internal energy, the interior lavas escaping through it, but, little by little, the solar crust will become continuous.

From that moment its cooling will take place more rapidly proportionally to the relative sizes of the two bodies than that of the Earth at the analogous period of its history for there will be no body at all to supply it with external heat. In a continual darkness, illuminated only by the light of the distant stars, the water-vapour of the solar atmosphere will be precipitated on its surface and form oceans there. Relatively soon after their formation they will become frozen. The gases of the solar atmosphere will condense in their turn and the Sun, also, will then be a globe, whose interior, containing an immense reserve of energy, will be for billions of centuries prevented from cooling by its non-conducting solid crust. The Sun will continue its journey through celestial space, leading with it its cortège of superficially cooled planets, like a great shell charged with a terrible explosive, formed by the endothermic compounds accumulated at its centre and maintained at a temperature of several million degrees.

The Earth also will be in a similar state, but on a much more modest scale, continuing to gravitate around its former Sun with an interior reserve of energy that only awaits a suitable occasion for renewed manifestation, for liberation with the accompaniment of a colossal production of heat.

The collision between two dark bodies in inter-stellar space appears to be the means whereby the rebirth or rejuvenation of a world takes place. The nearest stars are, however, at so great a distance from us that light, although travelling with a velocity of 300,000 kilometres [186,000 miles] per second takes ten years to traverse it.' There-fore, as our Sun is journeying towards the constellation of Hercules with a velocity of 20 kilometres [12.5 miles] per second, at least ten billion years must elapse before this distance can be covered and a collision be actually possible.

But there are not only luminous or living stars in space. We have supposed our Sun extinct and travelling through space. It may encounter a similar body, dark and therefore invisible to us, situated at a less great distance than the stars we see. The chances that such an encounter may occur, increase with the decrease of distance between the two bodies on account of the attraction, which increases in proportion to the square of the diminution of the distance which separates them. The mathematical theory of probabilities has been applied to this subject, and it is found that the probable time elapsing between two successive collisions of one body with others in a million million years, is about a hundred times as long as the duration of the life of a sun.

It has been calculated that the meteorites falling on the Sun do so with a velocity of 60o kilometres [362 miles] per second. We may then imagine our two celestial bodies coming together, each possessing a velocity of this kind. The collision will be doubtless oblique for the chances of meeting normally are much smaller. The shock will thus impress on the moving system a movement of rotation, the peripheral velocity of which will be enormous and will attain several hundreds of kilometres [or miles] per second.

Even if the two bodies so colliding were entirely solid, that is to say, if they were cold right through to the centre, the tremendous force of the shock, transformed into heat, would suffice to volatilise completely all the constituent matter. But we know that they may be and probably are great reserves of energy, full of endothermic compounds, the force of which is illustrated by the velocity with which are expelled the jets that actually form the solar prominences. This energy is certainly relatively thousands of times greater than that of our most terrible modern explosives. As to the possibility of such combinations, the continual disengagement of heat from radioactive substances is a familiar illustration. Endothermic combinations are formed throughout the evolution of suns during their period of brilliancy, and, in all probability, result from the union of hydrogen and helium with carbon and the metals.

When a collision occurs between two extinct suns these substances are decomposed into their ultimate elements, and set free an inconceivably vast quantity of heat.

Then the whole mass is volatilised to give birth to what we call a new star or nova, such for example as Nova Persei. Sometimes perhaps several such bodies might result from the impact, being separated from the original agglomeration of incandescent matter. Two gaseous lateral jets, the result of the obliquity of the impact, will shoot forth forming a spiral, with a velocity of several hundred kilometres [or miles] per second, and the gas composing them will constitute the spiral arms of a new nebula, whose nucleus or nuclei will be stars in process of birth. Thus, there comes into being a nebulous system, with a star in its centre, and all the phases through which our Sun and planets have been will reoccur in the new cycle.

Thus takes place the resurrection of a world.

And, once more, on the great dial of the sky where the life of suns is the measure of minutes, the clock of eternity will have accomplished one of its turns.