Why Is the Ocean Salty?
The ocean is salty because flowing water keeps adding dissolved minerals to the sea while only pure water leaves it. Rocks and soil on land contain tiny amounts of salt and minerals. When rain falls, it slowly dissolves these minerals and washes them into streams and rivers, which all flow downhill and eventually reach the sea, carrying their dissolved salt along the way.
The sea stays salty because of evaporation. The sun heats the ocean surface and turns water into vapour that rises to form clouds, but the salt is left behind — it cannot evaporate with the water. So fresh water keeps leaving the ocean while salt keeps arriving. Over billions of years, this one-way build-up has made seawater far saltier than rivers or rain.
Key ideas a learner will grasp: salt comes from rocks weathering on land, rivers transport dissolved minerals to the sea, evaporation removes water but not salt, and a slow process repeated over a very long time can produce a big result.
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A Salty Mystery🌊 Why Is the Ocean Salty? Have you ever swum at East Coast Park and got a mouthful of seawater? Yuck — so salty! 🧂 🧂 🧂 But rain and rivers are not salty. So where does all that ocean salt come from? Let's find out — tap Next to begin! 👉
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A Quick Taste TestFirst, a taste test 👅 Tap each glass to "taste" it. Can you guess which water is salty before you tap? Rain 🌧️ River 🏞️ Ocean 🌊 Tap a glass to taste it! Surprise! Only the ocean tastes salty. Rain and rivers taste fresh. So the salt must be collecting in the ocean somehow… 🤔
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Rocks Are Full of SaltLand is full of hidden salt 🪨 Rocks and soil have tiny bits of salt and minerals locked inside them. You can't see it, but it's there! Tap the rocks to crack them open and find the hidden salt grains. Salt found: 0 / 3 Crack open all 3 rocks!
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Rivers Carry It DownRain washes the salt to the sea 🌧️➡️🌊 When rain falls, it slowly dissolves that hidden salt and carries it into streams and rivers. Rivers flow downhill… all the way to the ocean! Ocean 💧 Send the salty water down! Press the button to follow a salty water drop.
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The Big Secret: EvaporationHere's the big secret ☀️ The sun heats the ocean. Water turns into vapour and floats up to make clouds. But here's the trick: The water leaves… but the salt stays behind! 🧂 🧂 🧂 ☀️ Heat it up (step 0/3) Press to evaporate the water, step by step.
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Why It Stays SaltySalt keeps coming, water keeps leaving 🔁 This has been happening for billions of years! Rivers keep adding salt, and the sun keeps taking only the water. So the salt builds up and up. There's one more secret source. Tap the seafloor to reveal it 👇 Tap the little chimney on the seafloor! Those are underwater volcanoes and hot vents! They puff out minerals and salts from deep inside the Earth — adding even more salt to the sea. 🌋
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You Be the ScientistYou be the scientist 🔬 The sun heats a cup of salty seawater until the water disappears. What is left in the cup? Nothing — it's empty A layer of salt 🧂 More water Pick the answer you think is right. Exactly! Water floats away as vapour, but salt is too heavy and stays behind. That's why the ocean stays salty! ⭐
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You Solved It!🏆You solved the salty mystery! Here's the whole story in 4 steps: 🪨Rocks and soil on land hold hidden salt. 🌧️Rain dissolves the salt and rivers carry it to the ocean. ☀️The sun makes water evaporate — but the salt stays behind. 🔁This repeats for billions of years (plus underwater volcanoes), so salt keeps building up. So: the ocean is salty because salt keeps flowing in, while only the water gets to leave. 🌊✨ Great work, young scientist! Next time you taste seawater, you'll know exactly why. 👏
Frequently asked questions
- Why is the ocean salty but rivers and rain are not?
- Rivers carry dissolved salt towards the sea, but they keep flowing, so the salt does not build up in them. In the ocean the salt collects because water leaves by evaporation while the salt stays behind. Rain is fresh because evaporated water leaves its salt in the sea.
- Where does the salt in the sea come from?
- Most of it comes from rocks and soil on land. These contain tiny amounts of salt and minerals that rain slowly dissolves, and rivers then carry into the ocean.
- If you boil away a cup of seawater, what is left?
- A layer of salt is left in the cup. The water turns into vapour and escapes, but the salt cannot evaporate, so it stays behind. This is the same effect that keeps the ocean salty.
- Is the ocean getting saltier over time?
- Salt has been collecting in the sea for billions of years, but the saltiness is fairly stable now because salt is also removed — for example when it settles to the seafloor or is used by sea creatures — so the amount added and removed stays roughly balanced.
- Why can't you drink seawater?
- Seawater holds far more salt than your body can safely handle. Drinking it would make you more thirsty, because your body needs extra fresh water to flush the salt out.
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