How do we know?
↻ One of the pages with a moving picture
A NASA instrument measured how salty the ocean is, from space.
- Rain falls on land and slowly wears away rocks. Tiny bits of salt and minerals wash out.
- Streams and rivers carry those bits all the way to the ocean.
- Sea creatures use up some of them. The rest stay in the water, so the salt builds up over time.
- Hot water from cracks in the seafloor, called vents, and underwater volcanoes add minerals too.
From 2011 to 2015, a NASA instrument called Aquarius measured how salty the ocean’s surface is, from space! It was a team mission with Argentina.
Photos from space also show rivers pouring water full of minerals into the sea. The Río de la Plata in South America pours it into the Atlantic Ocean.
When water leaves, salt stays behind. No river flows out of the Great Salt Lake in Utah, so the salt stays. It can be up to 8 times saltier than the sea!
Wow number
500 feet Scientists estimate that if all the ocean’s salt were spread over the land, it would make a layer more than 500 feet thick. That’s about as tall as a 40-story building!
Myth or fact?
Ocean water is about half salt. Myth. Only about 3.5% of its weight is salt.
Most of the sea’s salt is made of just two ingredients. Fact. Chloride and sodium make up about 85%.
Think about it
If rivers carry salt into the sea, why do you think rivers are not salty like the sea?
Where in the world?
Great Salt Lake, Utah, USA where no river flows out, so the salt stays behind. It can be up to 8 times saltier than the sea! Photos from space show the Río de la Plata in South America pouring water full of minerals into the Atlantic Ocean — 41.1667° N, 112.5° W.
Where these facts come from
Every number on page 40, and who measured it
This page explains how rain, rivers and seafloor vents bring salt to the sea, and what the salt is made of.
Why is the ocean salty? — NOAA's Ocean Service, U.S. ocean scientists
oceanservice.noaa.gov/facts/whysalty.html
We checked it on 31 October 2026
This page tells us how thick the ocean's salt would be if it were spread over the land.
Why is the ocean salty? — The U.S. Geological Survey, the government's Earth scientists
usgs.gov/faqs/why-ocean-salty
We checked it on 31 October 2026
This page tells us how salty the Great Salt Lake can get.
Great Salt Lake - Fifty years of change through satellite images — The U.S. Geological Survey, the government's Earth scientists
usgs.gov/centers/utah-water-science-center/science/great-salt-lake-fifty-years-change-through-satellite
We checked it on 31 October 2026
This page tells us that the Great Salt Lake has no outlet to the ocean.
Commonly Asked Questions About Utah's Great Salt Lake & Lake Bonneville — The Utah Geological Survey, Utah's Earth scientists
geology.utah.gov/popular/great-salt-lake/commonly-asked-questions
We checked it on 31 October 2026
This page shows the Río de la Plata from space and tells us how much of seawater is salt.
Why is the Ocean Salty? — The U.S. Geological Survey, the government's Earth scientists
usgs.gov/special-topics/water-science-school/science/why-ocean-salty
We checked it on 31 October 2026
This page tells us about Aquarius, which measured the ocean's saltiness from space.
Aquarius — NASA, the U.S. space agency
science.nasa.gov/mission/aquarius
We checked it on 31 October 2026
Has this changed?
Why the ocean is salty is not going to change.
What does change is our measuring: satellites keep checking how salty the ocean’s surface is.
Words from this page
- mineral
- A natural, solid ingredient found in rocks.
- vent
- A crack in the seafloor where hot water comes out.
- chloride
- One of the two main ingredients of sea salt, together with sodium.
Try it!
Find the salt in salty water.
1. With a grown-up, stir a spoonful of salt into half a cup of water. 2. Pour a little into a dark saucer. 3. Leave it on a sunny windowsill for a few days.
What happens: the water disappears into the air, but white salt crystals stay behind on the saucer.
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