Why is the Ocean Water Salty ?

Rain falls from the sky.

It lands on mountains, fills rivers, and

eventually flows into the ocean.

That same water, the exact same water,

then evaporates back into the sky and

falls as rain again.

The water goes around and around in a

continuous loop.

But here is the problem with that.

If rain is fresh

and rivers are fresh

and the water feeding the ocean has

always been fresh

why is the ocean salty?

Where did the salt even come from in the

first place?

And if water keeps cycling in and out of

the ocean, why doesn't that cycle wash

the salt away over time?

There is something happening here that

most people have never stopped to think

about. And when the full answer comes

together, it points to processes

happening miles beneath the ocean floor.

Processes that were completely unknown

to science until 1977.

If this is the kind of thing that keeps

your brain busy, subscribe so you never

miss a video like this. And drop a

comment below if there's anything about

this topic you don't fully understand

yet. I read every comment and reply

personally. Start with the numbers

because they put everything into

perspective. The ocean holds about 97%

of all the water on Earth. Its average

salinity is 3.5% by weight.

That means every single liter of

seawater carries about 35 g of dissolved

salts inside it.

That does not sound like much until you

scale it up.

If every grain of salt were pulled out

of the ocean and spread evenly across

all the land on Earth, every continent,

every mountain range, every desert, it

would form a solid layer 166 m thick.

That is roughly the height of a 40-story

building.

Covering everything. And the most

dominant substance in that layer would

be sodium chloride, the same thing

sitting in a shaker on a kitchen table.

Sodium and chloride alone make up about

85% of everything dissolved in the

ocean.

So, how did it all get there? The first

part of the answer starts on land

with rain. Rainwater is slightly acidic.

Not because of pollution. This is

completely natural.

As water vapor condenses in the

atmosphere, it absorbs carbon dioxide

and forms a weak solution of carbonic

acid.

When that acidic rain hits rocks and

soil, it slowly dissolves minerals out

of them. Sodium, calcium,

magnesium, potassium,

all pulled out of the rock and carried

away.

Those dissolved minerals flow into

streams. Streams feed rivers.

Rivers flow toward the ocean.

And they have been doing this without

stopping for billions of years. Here is

the critical detail.

Rivers do carry dissolved salts, but the

concentration is so low, around 0.01%,

that river water tastes completely

fresh. The salt is there.

It is just invisible at that scale.

But this is where the ocean behaves

differently from everything else.

When water enters the ocean, it

eventually evaporates back into the

atmosphere. But evaporation is a

purification process. Only the water

molecules leave.

Everything dissolved in the water

every mineral every ion stays behind.

The water cycles.

The salt does not.

Over millions and then billions of

years, that one-way accumulation built

up. Salt in, but never fully out. That

is the foundation of why the ocean is

salty.

That makes sense.

But it creates another question. Rivers

have been feeding the ocean for billions

of years, carrying dissolved minerals

the entire time. Hydrothermal vents,

which we will get to in a moment, add

even more. So, why is the ocean not

getting saltier right now? Why has

salinity stayed relatively stable for

hundreds of millions of years? The

answer is that salt does leave the

ocean, just through mechanisms most

people never think about.

Sea spray carries salt particles into

the atmosphere, where they travel inland

and eventually settle on land. Certain

minerals crystallize out of the water

and sink to the ocean floor as sediment,

permanently removing them.

And there is a chemical concept called

residence time that explains exactly why

some elements dominate ocean chemistry

while others barely register.

Sodium has a residence time of around

260 million years. That means once a

sodium ion enters the ocean, it stays

there, on average for 260 million years

before being removed.

Chloride's residence time is even

longer.

This is why those two elements dominate.

Not because they are added in the

largest quantities but because they stay

the longest.

Iron, by contrast, has a residence time

of only about 200 years. It enters the

ocean and gets removed almost

immediately on a geological scale, which

is exactly why seawater is not full of

iron.

The ocean's chemistry is not random

accumulation. It is a balance

shaped by how fast things enter and how

fast they leave.

But rivers and rain are only part of the

story.

There is a second source of ocean salt

that scientists did not even know

existed until 1977.

That year, a deep-sea research

expedition near the Galapagos Islands

sent equipment down to the ocean floor

and found something nobody expected.

Along the mid-ocean ridges

the massive underwater mountain chains

that run across the floors of every

major ocean

tectonic plates are constantly pulling

apart.

And through the cracks left behind,

seawater seeps down into the ocean floor

and comes into contact with superheated

rock far beneath the surface.

That water gets heated to temperatures

exceeding 400° C.

At that temperature, intense chemical

reactions happen. The superheated water

pulls minerals and metals directly out

of the surrounding rock. Then that

mineral-loaded water shoots back up

through openings in the ocean floor

called hydrothermal vents.

Some of these vents release dark plumes

of hot, mineral-rich fluid into the

surrounding seawater.

Scientists call them black smokers.

Before 1977, nobody knew this was

happening.

The discovery completely changed how

scientists understood ocean chemistry

and where ocean salinity actually comes

from. Here is the scale of it. The

entire volume of ocean water cycles

through these hydrothermal vent systems

roughly once every 10 million years.

Over geological time, that process has

added an enormous amount of dissolved

material to the ocean. But this is where

things get interesting. Hydrothermal

vents do not only add minerals, they

also remove some. Certain ions already

dissolved in seawater react with the hot

rock during circulation and get pulled

out of the water entirely.

This means hydrothermal activity

functions as both a source and a filter,

adding some substances while stripping

out others. It acts as a long-term

chemical regulator for the entire ocean.

And then there is a third source that

operates separately from both rivers and

hydrothermal vents. There are an

estimated 1 million underwater volcanoes

on the ocean floor. Many of them are

active. When they erupt, they release

gases and minerals directly into the

surrounding water. One of the key

substances released is chloride.

One of the two primary components of

sodium chloride.

Volcanic outgassing, both underwater

and on land, has been supplying chloride

to the ocean throughout Earth's entire

history.

Three separate systems. Rivers carrying

dissolved rock minerals. Hydrothermal

vents cycling seawater through

superheated rock.

Underwater volcanoes releasing gases and

minerals directly. All of them feeding

the ocean. All of them running

simultaneously for billions of years. If

you want to see what happens when that

input has no balance at all, look at the

Dead Sea. The Dead Sea sits between

Jordan and Israel. Water flows in from

the Jordan River, but there is no

outlet. The only way water leaves is

through evaporation. And evaporation, as

established, leaves everything dissolved

behind. The result is a salinity of

approximately 34%, nearly 10 times

higher than the open ocean. The water is

so dense that the human body floats in

it with almost no effort.

The AC Great Salt Lake in Utah works the

same way. So does Lake Assal in

Djibouti, where salinity reaches up to

40%.

These are not exotic exceptions. They

are simply accelerated versions of the

same process happening in the ocean,

just in enclosed systems with no

chemical regulation to keep things

balanced.

Most freshwater lakes avoid this fate

because they have outlets. Water flows

in and flows out, carrying dissolved

minerals away before they accumulate.

The Great Lakes drain through the St.

Lawrence River into the Atlantic.

The continuous flow resets the

chemistry.

The ocean has no equivalent outlet.

Water leaves only through evaporation,

which purifies the water, but leaves the

salt permanently behind.

Now, here is the part that most sources

skip entirely.

Ocean salinity is not just a geological

fact.

It is one of the primary forces

regulating Earth's climate.

Saltier water is denser than fresher

[music] water.

That density difference drives

thermohaline circulation, the global

system of deep ocean currents that moves

heat around the entire planet. Without

it, Western Europe would be dramatically

colder than it is today.

The entire climate system depends in

part on the fact that the ocean is

salty.

Salt also lowers the freezing point of

seawater to around -1.8°C.

That keeps vast areas of the polar

oceans liquid even in extreme cold,

which sustains polar ecosystems and

plays a direct role in regulating global

temperatures.

And the implications stretch even beyond

Earth. NASA scientists studying Europa,

one of Jupiter's moons, have found

evidence of a liquid ocean beneath its

frozen surface.

The leading theory is that this ocean

may be salty, driven by the same

hydrothermal processes happening on

Earth's ocean floor. If confirmed, it

would mean a salty ocean is not unique

to Earth. It may be a natural

consequence of liquid water and rocky

geology existing together anywhere in

the universe.

The ocean is salty because rain is

slightly acidic.

And that acid has been dissolving

minerals out of rocks and delivering

them to the sea for billions of years.

It is salty because hydrothermal vents

on the ocean floor cycle seawater

through superheated rock, loading it

with dissolved minerals. It is salty

because underwater volcanoes have been

releasing chloride into the water

throughout Earth's entire history. And

it stays salty because when water

evaporates, it leaves everything behind.

The ocean has no drain, and that changes

everything. If you made it to the end of

this video, subscribe. There is a lot

more where this came from. And if any

part of this raised a question you still

want answered, drop it in the comments.

I will be there and I will reply.