Sir Arthur Thomson 261 



one time the whole surface of the earth was covered by 

 one great shallow sea. In these seas life first appeared. 

 How it came we do not know, and this is not the place to 

 discuss this greatest of all problems. The first living 

 creatures were certainly very small. They were half 

 plants, half animals, which swam about in the warm, 

 brackish water, but it was they who began the process of 

 splitting up the heavy carbonic acid gas, fixing the car- 

 bon and liberating the oxygen, and so improving the air 

 and by degrees making it more fit to breathe. 



As the continents rose some of these living things had 

 a chance of settling down, and so began the race of sea- 

 weeds. In the course of ages the seaweeds worked up 

 the mouths of rivers into fresh water, changing by degrees 

 and very slowly into mosses and ferns. We know from 

 examination of the deep coal-measures that the early 

 forests consisted of giant ferns such as still exist in New 

 Zealand. 



Meantime there was another change taking place in the 

 seas. Some of the half -plants turned into animals. The 

 plants had been content to feed on what they could get 

 from air, water, and soil, but these new creatures would 

 no longer live in that way. They moved about and fed 

 upon the plants themselves, and so gained energy and 

 increased in size. 



" These," says Sir Arthur, " tried experiments along 

 many lines and gave rise to sponges, zoophytes, corals, 

 and jelly-fish.' ' Most likely they lived in the shallow 

 waters near the shores, creeping or swimming among the 

 beds of seaweed. We may be quite certain that animal 

 life began in the water and not on the land. 



One proof of this is open to every one, for if you cut 

 your finger and suck it you find that the blood has a 

 strong salty taste. The salts in your blood are almost 

 exactly the same as those in sea-water. 



Sir Arthur Thomson believes that the first living 



