Why does the ocean stay salty but rain is fresh?
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After you watchWhy does the ocean stay salty but rain is fresh?
The short answer
Rivers and other sources deliver dissolved salts to the ocean. Evaporation removes water while leaving most dissolved salts behind; other processes also remove salts.
Try this next
- What if another 25 water units evaporated? Use the shown counts to predict salt amount and concentration. This additional endpoint is a thought experiment.
Now you — bend it
- What if Replay the sample and compare its initial and final inventories.Track water and salt separately, then read the concentration. Each replay starts a fresh 100-water/10-salt sample.
- What if Thought experiment: remove another 25 water units from the final sample.Keep the salt amount fixed and recalculate salt per 100 water units. This additional endpoint is not simulated.
Can you prove it?Evaporation can increase concentration without increasing the amount of salt. — Compare the 10 fixed salt units with water falling from 100 to 50 in the model.
Design your own test:Predict both salt amount and concentration when a new fraction of water is removed.
Explain it to a 6-year-old: Water can evaporate while dissolved salt stays in the sample, making the remaining water saltier.
The whole story
How it works
The sample model starts with 100 water units and 10 salt units. After 50 water units evaporate into a separate collector, 10 salt units remain. Salt concentration doubles while the amount of salt stays fixed. The real ocean also exchanges water and salt through rivers, precipitation, minerals, and biological processes.
What people get wrong
More concentrated saltwater does not necessarily contain more salt. Removing water can raise concentration while salt inventory stays unchanged.
The catch
This sample isolates evaporation. It is not a whole-ocean salinity forecast or drinking-water demonstration.
Questions kids ask
Does evaporation create salt?
No. In this sample the dissolved salt amount stays fixed while water leaves, so concentration rises.
Why does the ocean have salt to begin with?
Weathering and other sources supply dissolved ions. Evaporation concentrates them, while other processes also remove them.
Is collected rain or water automatically safe to drink?
No. Low salt does not establish safe drinking water.
Talk about it
- Rain falls fresh but the sea it came from is salty — guess where the salt goes when the water lifts off.
- Rivers taste fresh, yet they're what makes the ocean salty. How do you think that works?
- The ocean has been getting salt for millions of years but isn't solid salt. What might be carrying salt back out?
For grown-ups
The sample model starts with 100 water units and 10 salt units. After 50 water units evaporate into a separate collector, 10 salt units remain. Salt concentration doubles while the amount of salt stays fixed. The real ocean also exchanges water and salt through rivers, precipitation, minerals, and biological processes. This sample isolates evaporation. It is not a whole-ocean salinity forecast or drinking-water demonstration.
Keep going
What else makes you wonder?
- Where does the salt in rivers come from in the first place?
- Why is the Dead Sea so salty you can float on top of it?
- Could an ocean ever dry up and leave a desert made of salt?