The Earth's rivers constantly carry dissolved salts into its oceans
Clearly, ttherefore, by taking the resulting increase in salt levels in the oceans over the past hundred years and then determining how many centuries of such increases it would have taken the oceans to reach current salt levels from a hypothetical initial salt-free state, the maximum age of the Earth's oceans can be accurately estimated
There are salts that leach into the Earth's oceans directly from the ocean floor