FIRE, ROCK, AND SEA 15 



resulting in planets, one of which is our earth. As the earth 

 cooled, some say, the surrounding vapor clouds rained down 

 and filled the basins formed in the shrinking crust and thus 

 began our Ocean River. Further, scientists are pretty sure the 

 creation of the earth and the firmament did not take place at 

 9 A.M. on the 23rd of October, 4004 b.c, as some theologians 

 have precisely determined. 



Astronomers have evolved a very accurate scientific clock 

 by their studies of the rate at which the moon appears to re- 

 volve around the earth. They use this to try and determine the 

 date when the earth assumed its solid state. Modern physicists 

 more exactly measure the age of the earth's crust by the rate of 

 radiation of such radioactive substances as uranium. But let 

 us first look briefly at the moon. 



At the present time the rate at which the moon circles the 

 earth is roughly once in every twenty-five hours. In passing 

 around the earth the moon tends to draw along with it, by 

 means of the gravitational force that exists in all particles of 

 matter, the thin skin of water we call the ocean, and so causes 

 the daily tides. If the surface of the earth were entirely liquid 

 the whole crust would move in this way, but it is solid, and so 

 the water alone moves in a worldwide tidal stream. There are 

 obstacles even to this. The narrow seas, bays, and estuaries in 

 particular hold back the free flow of water with the forces of 

 friction. Though these are relatively small they can neverthe- 

 less be estimated. Calculations have shown that in course of 

 time the results of such apparently insignificant obstacles may 

 be nothing short of catastrophic. 



Two of these results are of great importance. The first result 

 of the tidal brake is to slow down the moon's period of revo- 

 lution around the earth by an exceedingly small amount, 

 about one second in 120,000 years, as well as to slow down the 

 rotation of the earth itself. The cumulative effect of this, in 

 billions of years from now, will be that the length of our day 



