Oceans Become Saturated with Phosphates

assume that the rate of phosphate leached from surfaces is a function of surface area leached. As surfaces of a mass increase, rates of leaching increase by a factor k  

An estimate of k can be obtained by utilizing the estimate of Horn and Adams that 22.4 X 10 tons of phosphorus are contained in sedimentary deposits. Also, assume that to was 4.3 x 10 years ago. Then, 

Present quantities of phosphorus in the oceans of Earth have been estimated to be 9.8 X 10 tons. Therefore, 

It required about three billion years for all the oceans of Earth to become saturated with phosphates for the first time. Until then oceans acted as a giant sink for phosphorus, holding it in solution too dilute to be of much use as a nutrient to life forms. When Earth s oceans became saturated, any new dissolved phosphates entering the seas caused precipitation of exactly the same amount of phosphate someplace else. This action became faster and faster until today there is a complete replacement of phosphate in oceans every 4.9 x 10 years, a very short time on a geological time scale. This estimate is based upon the estimate of McKelvey et al. that 2x10 tons of phosphorus are delivered to the seas each year, and Horn and Adams estimate of the phosphorus in the seas.  

When oceans became saturated, large sedimentary deposits began to form more and more quickly and it was about 500 x 10 years before crustaceans and then vertebrates became plentiful. Phosphates are required for the formation of vertebrates since their framework is calcium phosphates. There is small reason to doubt that abundant life on Earth required abundant phosphates to support this life. Life was forced to await a source of phosphates. Not only are phosphates not harmful to life, phosphate fibers are one of the purer forms of phosphates known, and life cannot exist without phosphates. 

---

Retention times for most soluble salts are extremely long. The most abundant salt in oceans is sodium chloride. Oceans of Earth have never been saturated with this salt and it has never turned over once since Earth s beginning. This does not mean that local deposits have not formed in large quantities and that large quantities have not been removed and replaced. It merely means that oceans have not become saturated with respect to sodium chloride, potassium chloride, ammonium chloride, sodium nitrate, and other soluble salts as they have with calcium phosphates. ... 

---