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Asked by melbluetoffee to Clare, Dave, Glo, Ozge, Sean on 22 Jun 2011. This question was also asked by beckysage12.
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Clare Woulds answered on 21 Jun 2011:
Because the water flowing into the sea is rainwater flowing over land, and that dissolves salt out of rocks as it goes. When water leaves the sea it does it by evaopration, which means that pure water leaves and the salt stays behind, so the sea is saltier than river water (which does have a small amount of salt in it). Lord Kelvin once thought that we could work out how old the Earth is by seeing how much salt is in the ocean, and working out how fast it enters the ocean, however that doesn’t actually work as sometimes salt gets incorporated into rocks, and so leaves the ocean again.
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Dave Sproson answered on 21 Jun 2011:
Not much to add to Clare’s answer here, other than to mention that the saltiness of the ocean depends on where you are. For example, the Mediterranean is almost twice as salty as some parts of the Arctic Ocean!
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Sean Clement answered on 21 Jun 2011:
Clare has nailed it! Just want to touch on Daves additions. One of the reason that the Mediterranean is so salty is because of an event called the Messinian Salinity Crisis around 5.5 million years ago. This is completely by the by but it sticks in my head because it’s probably the coolest sounding event in the recent geological past…
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Gloeta Massie answered on 22 Jun 2011:
To make the fish taste better? 🙂 Another factor that only ‘recently’ was discovered were hydrothermal vents (which rock!). Yep – these vents spew forth all sort of dissolved salts (as do underwater volcanos!). Here’s a little blurb on this topic: http://ga.water.usgs.gov/edu/whyoceansalty.html
What’s really interesting about the discovery of the hydrothermal vents pumping out salts is that many of the myths surrounding why the sea is salty are based on the idea of a giant salt mill about the bottom of the sea that is pumping out salt. Sometimes myths are closer to reality than we give them credit for… 🙂
Have a read through of one of the myths: http://www.sacred-texts.com/etc/bnm/bnm40.htm
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