Why Is the Ocean Salty?

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They write new content and verify and edit content received from contributors.</div> </a> <div data-popper-arrow></div> </div> <span class="btn btn-link editor-link p-0 qa-byline-link gtm-byline font-12 byline-contributor text-decoration-underline"> The Editors of Encyclopaedia Britannica</span></div></div> </div> <article class="topic-content content mt-20"><figure class="md-assembly md-feature-assembly print-false" data-type="1" data-descid="1"><div class="md-assembly-wrapper card-media " data-type="image"><a href="https://cdn.britannica.com/65/161665-050-C4B1FA75/Waves-North-Shore-Oahu-Hawaiian-Islands.jpg" target="_blank" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center " data-href="*"><img src="https://cdn.britannica.com/65/161665-050-C4B1FA75/Waves-North-Shore-Oahu-Hawaiian-Islands.jpg?w=600&q=60" alt="Waves, North Shore of Oahu, Hawaiian Islands, United States." data-width="1600" data-height="1088" loading="eager"><button class="magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10" aria-label="Zoom in"><em class="material-icons link-blue" data-icon="zoom_in"></em></button></a></div><figcaption class=""><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div><cite class="credit d-block mt-5">Digital Vision/Thinkstock</cite></figcaption></figure><p class="topic-paragraph">“Water, water everywhere,/ Nor any drop to drink.” This famous line, spoken by the lost sailor in Samuel Taylor Coleridge’s poem <em>The Rime of the Ancient Mariner</em>, sums up one of the basic difficulties of life at sea: humans need water to survive, but seawater is too salty to drink. In fact, most of Earth is covered with undrinkable water; oceans cover 70 percent of Earth’s surface and account for about 97 percent of all water. The average salt content of ocean water is 35 parts per thousand, which—while it may not sound like much—works out to 120 million tons of salt per cubic mile of seawater. And there are about 332,519,000 cubic miles (1,386,000,000 cubic km) of water in the ocean. Where did all that salt come from?</p><span class="MOD1"></span><p class="topic-paragraph"><strong>It comes from the land, mostly. As rain forms and falls through the air, it accumulates carbon dioxide from the atmosphere, causing it to become slightly acidic. It then flows over the land, eroding rocks and picking up small amounts of salt and other dissolved minerals.</strong> At this point, the water is still basically fresh; there is some salt in it but usually not enough to make it undrinkable. Eventually, though, most rainwater finds its way to the ocean. Once it gets there, some of the dissolved minerals—such as calcium—are removed from the water by biological processes, but salt tends to remain. <strong>Additional salt is contributed by underwater hydrothermal and volcanic activity.</strong></p><span class="MOD2"></span><p class="topic-paragraph">The idea that salt was gradually deposited in the sea by rivers was first suggested by the British astronomer <a href="https://www.britannica.com/biography/Edmond-Halley" class="md-crosslink " data-show-preview="true">Edmond Halley</a> in 1715. Halley took his observation a step farther and proposed that salinity of seawater could serve as a kind of clock that could be used to determine the age of the ocean (and thus, he assumed, Earth). He reasoned that dividing the total volume of ocean water by the rate at which salt was deposited in the ocean would show how long it had taken for the ocean to reach its current level of salinity. Measurement techniques weren’t precise enough to perform the calculation in Halley’s time, but the Irish physicist John Joly tried it in 1899, coming up with an estimate of 90 million years. (More-advanced techniques later revealed this to be a major underestimate; the actual age is more like four billion.) Unfortunately, Halley’s scheme had been flawed from the start; among other problems, he had failed to account for the fact that some sea salt becomes sequestered in the form of mineral deposits on the seafloor.</p><span class="MOD3"></span><span class="AM-END-OF-ARTICLE am-inline"></span></article> </div> </div> </div> <aside class="cm-rightrail d-none d-md-block ad-rail"></aside> </div> </div> </div> </div> </main> <div class="grid gx-0"> <div class="col"> <div class="md-loading hidden display-4 font-weight-normal"></div> <div class="text-center my-20 mb-100"> <button class="md-infinite-load-next btn btn-blue" data-value="next-page">Load More</button> </div> </div> <div class="col-md-da-320 hidden-xs"> </div> </div></div> </div> </main> <div id="md-footer"></div> <noscript><iframe src="//www.googletagmanager.com/ns.html?id=GTM-5W6NC8" height="0" width="0" style="display:none;visibility:hidden"></iframe></noscript> <script type="text/javascript" id="_informizely_script_tag"> var IzWidget = IzWidget || {}; (function (d) { var scriptElement = d.createElement('script'); scriptElement.type = 'text/javascript'; scriptElement.async = true; scriptElement.src = "https://insitez.blob.core.windows.net/site/f780f33e-a610-4ac2-af81-3eb184037547.js"; var node = d.getElementById('_informizely_script_tag'); node.parentNode.insertBefore(scriptElement, node); } )(document); </script>  <script> window.ap3c = window.ap3c || {}; var ap3c = window.ap3c; ap3c.cmd = ap3c.cmd || []; ap3c.cmd.push(function() { ap3c.init('ZO4siT4cLwnykPnzZWJtd3Byb2Q', 'https://engage.email.britannica.com/'); ap3c.track({v: 0}); }); ap3c.activity = function(act) { ap3c.act = (ap3c.act || []); ap3c.act.push(act); }; var s, t; s = document.createElement('script'); s.type = 'text/javascript'; s.src = "https://engage.email.britannica.com/app.js"; t = document.getElementsByTagName('script')[0]; t.parentNode.insertBefore(s, t); </script> <script class="marketing-page-info" type="application/json"> {"pageType":"Story","templateName":"DEMYSTIFIED","pageNumber":1,"pagesTotal":11,"pageId":6076,"pageLength":null,"initialLoad":true,"lastPageOfScroll":false} </script> <script class="marketing-content-info" type="application/json"> [] </script> <script src="https://cdn.britannica.com/mendel-resources/3-130/js/libs/jquery-3.5.0.min.js?v=3.130.14"></script> <script type="text/javascript" data-type="Init Mendel Code Splitting"> (function() { $.ajax({ dataType: 'script', cache: true, url: 'https://cdn.britannica.com/mendel-resources/3-130/dist/story-page.js?v=3.130.14' }); })(); </script> <script class="analytics-metadata" type="application/json"> {"leg":"D","adLeg":"D","userType":"ANONYMOUS","pageType":"Story","pageSubtype":"DEMYSTIFIED","articleTemplateType":null,"gisted":false,"pageNumber":1,"hasSummarizeButton":false,"hasAskButton":false} </script> <script type="text/javascript"> EBStat={accountId:-1,hostnameOverride:'webstats.eb.com',domain:'www.britannica.com', json:''}; </script> <script type="text/javascript"> ( function() { $.ajax( { dataType: 'script', cache: true, url: '//www.britannica.com/webstats/mendelstats.js?v=1' } ) .done( function() { try {writeStat(null,EBStat);} catch(err){} } ); })(); </script> <div id="bc-fixed-dialogue"></div> </body> </html>

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Why Is the Ocean Salty? | Britannica