Interesting historical fact: The salinity of the Earth's oceans was proposed as a clock for measuring the Earth's age by Halley in 1715. This method ultimately arrived at ages around 50 million years (it didn't account for salt losses due to tectonic activity) and was one of the major stepping stones towards establishing public confidence in the idea of an "old" Earth.

But Earth is about 4.54 billion years old [1].

[1] https://www.space.com/24854-how-old-is-earth.html

50 million years is an improvement over textual Bible belief of five thousand.

Hence my comment about how they didn't account for salt being lost due to tectonic activity. Lose salt, and you get an underestimate of the age of the oceans.

The oceans are not saturated with salt, and there aren't many processes that extract salt from the ocean, but the process that made the oceans salty to begin with continues.

Also, the Earth is slowly losing its atmosphere, and with it -presumably- some water.

Of course, there's still a lot of water in rocks, so it's possible that the oceans could gain water and thus less salty.

But my guess is it's getting saltier.

Any idea about this line from the seeker article above?

> "Salt ions themselves aren't added or removed from the ocean, but water molecules are freely gained or lost through the processes of evaporation and precipitation, or freezing and melting of ice," said Ruth Curry, a senior research specialist at the Woods Hole Oceanographic Institution.

"Salt ions aren't added". That doesn't seem right...

Woods Hole is a fine research institution. I think you can assume they were trying to make the concept accessible to layman.

And I think they are trying to not get into all the complexities (yes, Na+ and Cl- ions are added/removed in some natural processes, but many times less readily than water). One could easily point tectonic processes and salt loss via evaporite layer deposition, but you don't lose a lot by not going into the weeds.

O2 and H2O are both too heavy to escape earth.

Earth loses few kilograms of hydrogen and tens of grams helium per second to space.

How come the H and He don't just form a layer on top of our Nitrogen atmosphere? Why do they achieve escape velocity when they go into space?

Thermal loss. The molecules in a gas have certain kinetic energy distribution. Highest energy H and He atoms reach escape velocity in the upper part of the atmosphere.

Earth's magnetic field protects it from solar winds so Earth is not losing significant amount of any heavier atoms or molecules.

Solar wind must play a big part.