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Why Is The Ocean Salty?

Jamie Hayes

Why Is the Ocean Salty?

The ocean is vast, unpredictable, and…salty. But why is the ocean salty? Rivers and lakes aren’t salty. The water in your tap isn’t salty (if you’re lucky). So why the ocean? Well, interestingly enough, the ocean actually wasn’t always salty—but a few billion years and some basic chemistry later, and we’re left with the saline seas we’ve got today. So how did it happen?


Ancient Oceans

When the Earth’s oceans first formed, it’s very likely that they were only a little salty. However, the water cycle of evaporation, clouds, and rain eventually changed all that. Soon enough, there were trillions of tons of salt in the ocean—and it all came from rocks on the land. But let’s back that up a bit more.

It might surprise you to know that rain isn’t pure water. It contains, among other things, dissolved carbon dioxide from our atmosphere. This forms carbonic acid and makes rainwater very slightly acidic. No, it won’t melt the clothes off your back, but it does mean that rainwater can dissolve minerals. Though it’s a slow process, the carbonic acid in rainwater will dissolve the rocks it passes over, picking up ions in the process. Among these ions are sodium and chloride—which make up, you guessed it, salt.

Something Doesn’t Add up

As the rainwater splashes on the rocks and ends up in the ocean, it deposits these salty ions. But wait, that doesn’t quite make sense, does it? Shouldn’t that mean that lakes and rivers would also be salty? Well, no. There certainly are mineral ions in rivers and lake water, but these ions tend to flow into the ocean and out of freshwater.

Plus, the ocean is very, very old, which has allowed a long time for salt to build up in it. But wait, there’s more! Eventually, thanks to various natural processes, this process of salt depositing has reached an equilibrium, which is why the ocean doesn’t keep getting saltier and saltier.

But Where’s all the Pepper?

So why is the ocean salty? We’ve just answered it! Before that balance was reached, however, a lot of salt was deposited in the ocean. In fact, it’s estimated that if you took all of the salt out of the ocean, it would cover the entire Earth’s land surface…in a layer that’s 500-feet thick. That’s a little salty for my tastes. I think I’ll leave it in the ocean, thank you.

Sources: 1, 2


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