RIVER OF LIFE 43 



opportunity for a great surge of life. No longer restricted, as 

 the bacteria were, to their specialized chemical foods, which 

 were relatively limited in amount and distribution, the minute 

 prototypes of our modern plant world must have burst into a 

 great profusion of growth as a result of their new-found ability 

 to use the food salts and carbon dioxide in the ocean. This in 

 turn allowed some descendants of the original life form to 

 evolve as animals, which need ready-made plant or animal 

 material for their food. 



The first animals were most probably very simple creatures 

 drifting in the water. The growing powers of movement, char- 

 acteristic of animals, were soon encouraged by the greater abil- 

 ity to catch food which greater mobility provides, and by the 

 greater resultant energ}^ The increase in size and complexity 

 over millions of years must also have brought these primitive 

 creatures to a point where those that began to develop a sup- 

 porting skeleton had a great advantage over the others. Not 

 only do larger bodies need support and protection, but muscles 

 work more effectively when attached to a firm framework. As 

 soon as this hard body framework or a protecting shell was 

 formed, the sea creatures began to leave their remains within 

 the sediments for mankind to studv hundreds of millions of 

 years later. 



Thus it is hardly surprising that the first well-defined forms 

 of life found in the uplifted rocks of the ancient Cambrian sea 

 floors are not simple microscopic creatures. All these early 

 fossils, buried in the sediments which accumulated over 400 

 million years ago, when the Pre-Cambrian mountain build- 

 ing had died down, possess some hard parts that have defied 

 the destruction of time. With the exception of certain rather 

 doubtful remains, the geological record begins not with bacteria 

 but with corals, sponges, worms, and above all the trilobites 

 which were the dominant forms of those early days. The Cam- 

 brian seas were not like ours. No schools of fish swam in search 



