The Sea Does Not Have Enough Minerals
There is not enough salt in the sea or mud on the sea floor for the seas to be billions of years old.
Every year, salt accumulates in the ocean from rivers. Given the present rate it is increasing per year, the current 3.5 percent ocean salinity is much too low if this process has been going on for a very long time.
Mud enters the seas through rivers and dust storms. This occurs at much faster rates than plate tectonic subduction can remove it. Each year, 19 billion tons of mud accumulates. If the oceans were ancient, the oceans would be choked with sediment dozens of kilometers deep.