Tell Me Why the Ocean Is Salty
The Kid's Answer
Sy (left), age 4: A girl dumped a glass of salt into the ocean because it was sick and then the saltwater got into a whale's mouth and the whale sneezed.
The Parent's Answer
Bridgette, Sy's mom: Salt is a natural element that's found in the ocean; it's generated from things on the ocean floor, like coral reefs. The debris that fish give off probably has something to do with it too.
The Scientist's Answer
Rivers are the main sources of the oceans' salt, says David A. Ross, Ph.D., scientist emeritus of the Woods Hole Oceanographic Institution in Woods Hole, MA. They erode minerals from rocks and soil, and deposit them into the oceans or, in some cases, lakes. Those elements include sodium and chloride, which when combined become the same stuff that seasons your French fries. We're not talking a pinch here. Drain the world's oceans and you'd have 50 million billion tons of salt. And although rivers transport salt, they themselves don't become salty because the oceans are their dumping ground.
Freshwater from the rivers evaporates as the sun warms the oceans; the salt stays behind. "All the sodium and chloride that comes into the ocean stays there forever," Ross says. Or close to it. On average, an atom of sodium remains in the ocean for 200 million years.
That doesn't mean the oceans are slowly filling up with salt. This is because a good deal of the salt sinks into sediment on the ocean floor.
How to Explain It to Kids
Show them instead. To illustrate how the salt gets to the ocean in the first place, spread out a map, pick a river, and together trace its path to its only destination: the ocean.
To demonstrate how freshwater evaporates, leaving salt behind, try this kitchen-counter experiment: Add a tablespoon of salt to a glass of tap water, place it in the sun, and watch what happens. The liquid, like the fresh river water, disappears over the course of about a week, leaving a crust of salt, just as it would in the ocean. Not enough to start your own sea, but perhaps just the right dash to make a whale sneeze.
