08-30-2009 - Water

When water precipitates out of the atmosphere, it falls as freshwater. This freshwater – whose origin is rain – is what you’ll find in river, lakes and the underground aquifers that supply water for humans, animals and plants.

The freshwater that falls onto land also cascades over surfaces like rocks and sediments. As water moves over Earth’s surface, it picks up nutrients, chemicals, and salts. The water carries the dissolved salts on its journey back to the ocean. That’s why the ocean is salty. Over Earth’s four-and-a-half billion years, a lot of salt has been carried from land into the ocean.

Now imagine a tea kettle. Every time you boil tap water to make tea, some of the water evaporates. After a while, you might notice a hard crust of mineral deposits forming on the bottom of your teapot. That crust is there because – when tap water evaporates – it leaves behind dissolved salts and minerals.

Likewise, as water evaporates from the surface of the ocean, it leaves behind dissolved salts. These salts stay in the ocean while the evaporated water – the freshwater – rises into the atmosphere, eventually to fall again as rain.

That’s why, if you came back in another billion years, the ocean would be even saltier than it is now!

Written by EarthSky

No Responses to “Why are oceans salty but rivers and lakes are not?”

1. amber says:

   November 18, 2009 at 5:09 pm

   the ocean is salty
2. Latiyah latimer says:

   January 15, 2010 at 9:27 am

   why is the oceans salty and not the rivers and lakes