THE ORIGIN OF THE EARTH 423 



For the building up of the solar system, the planetesimal hypoth- 

 esis starts with a spiral nebula consisting of the following elements : 

 (1) the main knots to serve as nuclei for the planets, (2) small 



Fig. 336. Theoretical restoration of the parent nebula of the solar system. 

 The nuclei of the several planets may be identified by their distances 

 from the center. The dimensions of the inner parts are made dispro- 

 portionately large. 



scattered knots as the nuclei of the asteroids, (3} other small 

 knots near to the large knots and controlled by them, as the nuclei 

 of the satellites, and (4) scattered matter or nebulous haze to be 

 gathered into these nuclei to give them their mature sizes, and (5) 

 the great central mass of the nebula, forming the nucleus of the sun. 

 The gathering of the scattered planetesimals into the knots to form 



