THE EARTH THE ABODE OF LIFE 



not of the highest forms of life). From that we infer 

 that life must have existed many ages before the period 

 of such remains, though, as we should have expected, all 

 examples of the earlier forms have disappeared. 



Where did this life come from ? Lord Kelvin once 

 rashly committed himself to the notion that life might 

 have been brought to the earth on one of those flying 

 pieces of rock, which we have already spoken of, which 

 are named meteorites, or on a fragment of some other 

 planetary body that had been cast out into space. The 

 speculation is not so wildly improbable as it has some- 

 times been considered to be, because recent researches 

 have shown that it is not impossible for life to survive at 

 the very low temperatures which a meteorite would ex- 

 perience on its way through space, and also that the time 

 which a small body would occupy in travelling, let us say 

 from Mars to the earth, would not be too great for the 

 prolonged existence of some germ of life on the meteorite. 

 On the other hand, there is nothing in known meteorites 

 to suggest that they came from worlds where conditions 

 exist suitable for life as we know it ; and, moreover, even 

 if we shut our eyes to these improbabilities, we are no 

 nearer to a solution of the problem of where and how 

 life began. To say that it was brought to earth on a 

 meteorite is merely to throw back the problem another 

 stage, for we have still to ask how life began on the 

 meteorite and on the planet from which it came. The 

 indirect evidence regarding the probable beginning of 

 the era of life on the earth is also extremely difficult to 

 examine, and we can only say that the best geological 

 H 113 



