Humphreys' salt in sea water calculation puts the earth's age at 42 million years.
The salt in sea water likely got there 4500 years ago when the “fountains of the great deep” ruptured, bringing the salt to the surface.
Anyway, there is no basis for age determination by the presence of salt, unless you assume distilled water to start, and a constant rate of accretion,which is illogical on it’s face.