Ask most people to name the longest mountain range on Earth and you\u2019ll hear the Andes, or maybe the Himalayas. Both are wrong, and not by a little.<\/p>\n
The real answer is a chain of undersea volcanoes almost no human has ever seen. NOAA calls it the longest mountain range on Earth<\/a>, running nearly 65,000 kilometers, roughly 40,390 miles, around the planet. That\u2019s several times the length of the Andes. And more than 90 percent of it sits underwater<\/a>, which is why you\u2019ve probably never seen a photo of it.<\/p>\n It\u2019s called the mid-ocean ridge. It curls down the middle of the Atlantic. What strikes me is how completely it flips the mental map most of us carry. We picture Earth as continents with some water in between. The truth is closer to the reverse.<\/p>\n How a woman who wasn\u2019t allowed on the ships mapped it<\/p>\n A rough hint of an underwater ridge in the Atlantic had turned up in the 19th century, when ships measured ocean depths while laying telegraph cables. The modern picture came from the 1950s, and it came from a mapmaker named Marie Tharp<\/a>, working at Columbia University\u2019s Lamont Geological Observatory. Because women were not typically allowed on research ships<\/a> at the time, Tharp worked on land, turning the depth readings the men brought back into hand-drawn profiles of the ocean floor.<\/p>\n As she plotted the North Atlantic, a deep notch kept appearing along the crest of the ridge, a valley running down its spine. To Tharp it looked like a rift, a place where the crust was pulling apart. Her collaborator, the geologist Bruce Heezen, wasn\u2019t convinced. As Tharp later told it<\/a>, his first reaction was to wave the idea away: \u201cIt cannot be. It looks too much like continental drift.\u201d At that point, the idea that continents move was still widely dismissed.<\/p>\n Tharp\u2019s own account of the standoff is my favorite part of the story. She didn\u2019t argue the theory. \u201cI was so busy making maps I let them argue,\u201d she said<\/a>. \u201cI figured I\u2019d show them a picture of where the rift valley was and where it pulled apart.\u201d<\/p>\n The first Atlantic map appeared in 1957<\/a>, and the complete world map of the ocean floor, painted with the artist Heinrich Berann, followed in 1977<\/a>. Their work helped push the theory of moving plates from fringe idea into textbook science.<\/p>\n What it actually looks like down there<\/p>\n The ridge isn\u2019t a mountain range in the way we usually think of one. It sits where tectonic plates pull apart and magma rises to fill the gap, hardening into fresh ocean crust. The top of the ridge sits around 2,500 meters down<\/a> on average, about 8,200 feet of water overhead.<\/p>\n Tharp had a plain way of putting the scale of it<\/a>. \u201cYou can\u2019t find anything bigger than that, at least on this planet,\u201d she said.<\/p>\n Why this should change how you picture Earth<\/p>\n I keep coming back to this. We built our sense of what Earth is out of the roughly 29 percent<\/a> of it we can walk on. The other two-thirds is a landscape we\u2019ve barely glimpsed.<\/p>\n Even now, after decades of sonar and satellites, only a fraction of the seafloor has been mapped in real detail. A 2025 review in Frontiers in Marine Science<\/a> tracked detailed coverage rising from 6.2 percent in 2014 to 26.1 percent by 2024. By April 2026, NOAA put the figure at 28.7 percent<\/a> mapped with modern high-resolution tools.<\/p>\n Mapping isn\u2019t the same as seeing, either. Explorers have actually laid eyes on less than 0.001 percent of the deep seafloor<\/a>, according to NOAA. Derek Sowers of the Ocean Exploration Trust described the job ahead as a push to<\/a> \u201cfocus on exploring the 74% of global marine waters that are still unmapped,\u201d a figure from mid-2024 that shifts as surveys continue.<\/p>\n Tharp understood what her maps did. They gave people, as she put it<\/a>, \u201ctheir first relatively realistic image of a vast part of the planet that they could never see.\u201d Nearly seventy years later, that\u2019s still roughly where we stand. The longest mountain range on Earth runs beneath the waves, building the ground under two-thirds of the world, and we\u2019ve seen almost none of it. Perhaps the stranger thing isn\u2019t that the ridge is hidden, but that we\u2019ve been calling the visible sliver \u201cthe world\u201d all along.<\/p>\n Editorial process<\/p>\n \n\t\t\t\tSpace Daily articles are produced with AI assistance and reviewed by editorial staff before publication. See our editorial standards<\/a> and masthead<\/a>.\n\t\t\t<\/p>\n","protected":false},"excerpt":{"rendered":"Ask most people to name the longest mountain range on Earth and you\u2019ll hear the Andes, or maybe…\n","protected":false},"author":2,"featured_media":808787,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[7],"tags":[49,48,66],"class_list":["post-808786","post","type-post","status-publish","format-standard","has-post-thumbnail","category-science","tag-ca","tag-canada","tag-science"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts\/808786","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/comments?post=808786"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts\/808786\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/media\/808787"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/media?parent=808786"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/categories?post=808786"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/tags?post=808786"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}