300 THE CHEMISTRY OF THE PRIMITIVE OCEAN [APP. I 



elsewhere and here the first seas would be formed. The primitive 

 crust would be thin and yielding, and as the interior was still liquid, 

 whenever a considerable mass of water fell on it, it would become 

 depressed, and in this way the first ocean beds would be formed. 



The composition of these first oceans would be very different from 

 that of the modern ones. At first, for a very short time, the water in them 

 would be almost pure but soon salts would accumulate, (1) from the 

 solution of the materials present in the original crust of the earth, 

 and (2) from the solution of the salts present in the rocks of the dry 

 land, and brought down in solution by the rivers. In the water of 

 these first rivers the salts would be present in proportions depending on 

 the relative amounts in which they were present in the rocks, and also 

 on their relative solubilities. The composition of the sea would soon 

 become very similar to that of the rivers. Potassium and sodium 

 would probably be very nearly equal in amount ; possibly magnesium 

 would be more abundant than sodium, and calcium more abundant 

 than either. Changes would soon take place in the composition of 

 the water of the primitive sea, for mutual reactions between the 

 various salts would take place. 



By-and-by life appeared in the sea and then further changes 

 would take place in the composition of the ocean salts by reason of 

 the action of living organisms. Calcium would be precipitated, for this 

 element would be secreted by organisms to form their limy skeletons, 

 and when they died the skeletons would sink to the sea bottom and 

 accumulate. Some magnesium would also be precipitated, for we find 

 this element in association with lime as magnesian limestone. 

 Potassium would be precipitated as glauconite, a mineral which is 

 formed by organic action. The decomposing dead matter of organisms 

 liberates sulphuretted hydrogen, which then combines with iron to form 

 ferrous sulphide, and then the sulphur of this compound is oxidised to 

 form sulphuric acid. This acid acts on finely divided clay and sets free 

 colloidal silica, and the ferric hydrate present combines with this to 

 form a silicate and this then reacts with potassium salts to form 

 glauconite. In this manner and by other means the excess of 

 potassium originally present in the sea was gradually eliminated from 

 solution. Whenever life began to increase in the sea these reactions 

 would take place, and thus the calcium and potassium originally 

 present in excess would be reduced in amount. Sodium is not 

 removed from the sea in any great amount. Small seas may 

 dry up and their salt contents may pass out of solution, but 



