Have the Pacific and Atlantic Oceans always contained saltwater, or did they once have freshwater?

The Pacific and Atlantic Oceans have always contained saltwater, as they were formed millions of years ago from the cooling and solidification of Earth's early molten rock. While the oceans have experienced fluctuations in their salt content over time, they have never been completely devoid of saltwater.

The concept of saltwater versus freshwater is an important one in understanding the science of the oceans. The salt in seawater comes from the minerals in Earth's crust, which are eroded by water and carried to the ocean by rivers and other sources. Seawater also contains various dissolved gases, nutrients, and other substances that support marine life and contribute to the complex chemistry of the oceans.

The salinity, or salt content, of seawater varies from place to place, with the highest concentrations typically found near the equator and the lowest near the poles. This is due to a variety of factors, including evaporation, precipitation, and the circulation of ocean currents.