Science

A Famous Seafloor Map

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The 1977 Ocean Seafloor Map created by Bruce Heezen and Marie Tharp

One of the most famous world maps is the 1977 Ocean Seafloor Map (see above) created by Bruce Heezen and Marie Tharp, a pioneering female oceanographer and kick-ass female scientist. Prior to the publication of this map, scientists had very little idea of what the seafloor looked like on a global scale. Although the concepts of mid-ocean ridges and plate tectonics seem innate to the work of oceanographers and geochemists today, these concepts are remarkably recent in their development. Plate tectonics was not fully accepted by the scientific community until the late 1960s and early 1970s, and this first great seafloor map was not published until the late 1970s. Mid-Ocean ridges were not discovered until the work of Tharp in the 1950s and 1960s.

To this day, scientists still know relatively little about the seafloor. Modern technology is making mapping the seafloor easier, but to obtain detailed information one really must go out in a boat and take many days to carefully study a section of seafloor. Research cruises to map the seafloor are expensive and not always practical. Remote sections of the ocean or places where there is bad weather are difficult to impossible to map. Geologists actually know more about the topography of the moon and other terrestrial planets, such as Mars, than they know about the topography of Earth’s own ocean floor.

Prior to the pioneering work of Heezen and Tharp, almost nothing was known about the topography of the seafloor. The advent of new technologies to study bathymetry and the dedicated work of Heezen, Tharp, and other oceanographers shed some light on the dark, unknown ocean floor. Tharp carefully mapped the Atlantic ocean and discovered the Mid-Atlantic Ridge, a giant chain of mountains running along the middle of the ocean. At first, no one believed Tharp’s discovery of mid-ocean ridges. In the days before plate tectonic theories had been worked out and generally accepted, having a giant mountain chain in the middle of an ocean didn’t make much sense. There was no obvious reason why such a mountain chain should occur in the middle of an ocean.

Later, scientists realized that such ridges made perfect sense: mid-ocean ridges represent places where two oceanic plates are moving apart and new oceanic crust is forming from volcanic eruptions. At a mid-ocean ridge, the young, hot lava is bouyant and creates a topographic high. As the oceanic crust moves away from the ridge and ages, it cools and becomes more dense. The crust contracts and also sinks lower into the mantle, creating a topographic low. Thus, the ocean is shallower at mid-ocean ridges and deeper in the middle of oceans and also at subduction zones, places where the oldest, densest oceanic crusts subducts underneath lighter continental crust.

The famous 1977 seafloor map of Heezen and Tharp was a revolutionary map for the worldview of oceanographers. All of a sudden, oceanographers had an elegant, dramatic picture of the mid-ocean ridges running through the world’s oceans like seams on a baseball. The map made sense in the framework of the new science of plate tectonics. Although new data on the seafloor has been collected using modern techniques such as multibeam bathymetry (bouncing waves off the bottom of the ocean to calculate topography) and satellite altimetry (using the height of ocean waves to look for gravity anomalies and infer the topography below), the 1977 Heezen and Tharp map is still remarkably accurate, especially considering they made up (honestly– they didn’t deceive anyone) parts of the map where they had no data.

Heezen and Tharp’s 1977 seafloor map is also remarkable for its aesthetic beauty. The map was actually painted by a famous landscape and panorama artist named Heinrich Bernann, a very talented Austrian painter. Bernann masterfully captured the dramatic mountain-ranges of the mid-ocean ridges in his painting.

Bruce Heezen died many years ago, and Heinrich Bernann died a few years back. Marie Tharp just died last year at the age of eighty-six. Here’s to a great female oceanographer and scientist. I hope that my career in oceanography has a tenth of the influence Marie’s career did.

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Marie Tharp in 2001

Evelyn

Evelyn is a geologist, writer, traveler, and skeptic residing in Cape Town, South Africa with frequent trips back to the US for work. She has two adorable cats; enjoys hiking, rock climbing, and kayaking; and has a very large rock collection. You can follow her on twitter @GeoEvelyn. She also writes a geology blog called Georneys.

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18 Comments

  1. WOW! i never realized that that map had been created so recently. i was six when it was published and am pretty surprised, judging by what i hear about that state of science education in these here united states, that i was taught about plate tectonics when i was in fifth or sixth grade. i'm fairly confident that i was still in grade school when i first heard about this. i guess it is possible that i was exposed to it through the tv program NOVA and not in school, but i think there were books involved. it's hard to remember back that far though and i could be mistaken. anyway that is a very cool map and an impressive feat.

  2. Excellent, Evelyn. I love posts like this where several people get the credit – the oceanographers, the map-makers, et al. I love maps, too.

    Just this:

    "Ridges are places where the oceanic crust. The young, hot lava is bouyant and creates a topographic high'"

    Something happened with your sentence construction here…places where? Where new crust is formed? Thought you might want to fix that in an otherwise well-written (as usual) post. :-)

  3. I think they started mapping parts of the sea floor during world war two. Sonar was in its infancy, and submarines were essentially given the task of making an image of the sea floor inbetween or on their way to various gigs.

    Plate tectonics was an idea that had already been around for a long time because people had noticed how nicely Africa and South America fit together. They just didn't know how the plates moved.

    I didn't know it was only this recently that the proof was found to support that theory.

    On the other hand, people didn't think much of the idea of giant asteroids impacting on the earth's surface until around that same era. The extinction of the dinosaurs as being caused by such an event logically being even more recent than that.

  4. melusine:Thanks so much! The sentence is fixed (I hope!).

    exarch: You bring up some good points. You're right that much of the seafloor was mapped earlier. The Navy mapped large portions of the ocean much earlier, but their seafloor maps were confidential for many years. In many cases, oceanographers had to re-map portions of the seafloor already mapped by the Navy. Later on, the Navy did realease much of their seafloor data. Again, civilian efforts to map the seafloor started much earlier than 1977, but it was not until this year that the first real, global seafloor map was published.

    Also, Exarch, it is true that continental drift and other ideas related to plate tectonics were put forward by some individuals. However, the theory of plate tectonics was not accepted by the scientific community until the late 60s and early 70s.

    As for the famous K-T boundary extinction that killed the dinosaurs, a meteorite impact is not the sole explanation put forward by the scientific community at present. Personally, I think that the dinosaurs were killed off by a one-two punch of a meteorite impact and a large volcanic eruption in India. The Deccan Flood basalts (which I studied for my senior thesis as an undergrad) were erupted aboout 65 million years ago. The Deccan basalts represent an enormous eruption (millions of cubic km) over a very short period of time (about half a million years). The large volume of volcanic gases released by this eruption may have contributed to the dinosaur's demise. These volcanic gases possibly contained toxic metals and were of course also greenhouse gases– they heated up the planet.

  5. Evelyn,

    I'm not sure about the timing, but I seem to recall that, during my 'Age of the Dinosaurs' class as an undergrad, the professor mentioned that some people think the meteorite impact might have caused or worsened the Deccan eruption. The assumption was, I believe, that such a large impact on THIS side of the earth could have sent shockwaves and energy through the Earth itself and had an effect on the pressure of the magma pools in India.

    I'm not sure how much REAL thought has been put into this and how much was just conjecture on the part of a geology prof teaching an entry-level, gen. ed. requirement-filling undergrad course. What do you know about it??

  6. Expatria: I think it's unlikely that a meteriote impact caused or worsened the Deccan eruptions. I've read a couple of papers on the topic, but mostly the hypothesis been dismissed by the scientific community (not that such a dismissal means it's wrong!). I just don't see how energy can be transferred to trigger an eruption. Keep in mind that Earth's solid core is in the way! Scientists don't really understand how hotspots and flood basalts start anyway– that's where my research comes in.

    How about I write up a blog on the dinosaur extinction? Give me a couple of days.

  7. Evelyn

    Please, please write up a post about dinosaur extinction – that would be great. I am a science layman (interested but with no science education past high school) and I always learn interesting things when I read your posts.

    Thanks

    Monika

  8. Evelyn, the dinosaur extinction would be a great post, especially from your perspective. As I posted on BA, I was having a grand 'ol time watching this old Sikhote-Alin meteorite documentary while you guys were frying up your Twinkies, onions, and ~ugh~ Gummie worms. I love these kind of old documentaries of expeditions (like Shakleton et al) because these places were so hard to get to (in this case Siberian tigers and all) during those times.

    Anyway, comparing crater sizes, meteorites, depths, etc. to things I can relate to was loads of fun (yes, I did say that), especially since I bought a small Sikhote-Alin meteorite, plus some okenites (they're so cute) and lodestone to play with. If you know of any old films such as the one I posted, please share. The Sikhote-Alin meteorite covered an area of 2km (1.24 miles), and left 93 craters, and so on, so imagining one of a 6 mile magnitude is quite fascinating.

  9. Thanks for clearing that up, Evelyn. I'd love to see a post about the Dino extinction as well, as I've been a huge dino buff since I was a child. Take your time on it, it'll be fascinating to me. Plus, the phrase 'Chicxulub crater' sounds like a euphemism, which is always fun :-P

  10. I read a book about Alfred Wegener and his theory of continental drift in the 1960s, when I was in elementary school. I remember feeling excited by my realization that everything was not already known, that scientific discovery was still happening, and especially, that the world was a dynamic, changing place.

    This is not news to me now. But I've never forgotten that lesson: Grown-ups don't know everything.

  11. Nice website. Id just been browsing maps of the seafloor and suddenly I'm faced with a skepchick! A refreshing find for my yellowing bookmarks. So seeking the truth often drags me through the more pathetic but usually entertaining conspiracies and perpetual motion devices (a personal fave).

    And then I saw the neal adams http://www.nealadams.com/nmu.html site on the growing earth business. These things usually peg the old BS meter pretty quick. Take a look and suspend the – where the heck does the matter come from problem – this is very cool and well done even if its bogus. I enjoy the ways this theory is verifiable with your own personal globe and normal scientific data and no Diety meddling. And the whole India smashing up the Himilayas was never entirely convincing. Its so radical, but have you heard scientist writing about what dark energy and matter might be ? THEY DONT HAVE A CLUE , I/m convinced they are just grasping and they'll still be after they find the Higgs Boson. Im going to watch the inflating earth again….

    Skepchick what do you think ? Enjoy – and convince me this is crazy.

  12. Wow, if you need convincing that Adams is seriously way out there, I'm not sure even the scientists who regularly post here can do it. I hope you're joking, because you sound like an intelligent and curious person.

    And why should I or anyone else ignore the question of where the additional matter comes from? If Adams were writing science fiction, his explanation (as I recall it) might suffice, if his prose was good enough and I found the story consistent and amusing. But unless his entire site is a deliberate joke, one is left with the conclusion that he means what he says.

    If Adams' claims were true, it would be very evident. Current science can determine the mass of even distant stars with great precision. The mass and density of the planets of our own solar system are known quantities, and if they were subject to ongoing increase, that would be immediately observed and subjected to tens of thousands of independent investigations.

    I readily admit to no formal science background. Just a layman's interest in geology, planetography and astronomy, among others. I'm sure there are more knowlegeable contributors and posters who could better convince you.

  13. Thanks for your calm comments. I was just curious if other were struck by the elegance of the hypothesis. No subduction – less gravity – larger bugs – oil where all the shallow seas were – lots of possibilities on dinosaur extinction – ok its good geo-science fiction.

    Honestly, I'm more given to seeking out the Randi's and Dawkin's world view. And I wonder what it is that allows intelligent design and elaborate alien and 911 conspiracies to run amok unchecked in society. This one is different because it appeals to the scientific side of my brain and doesn't offend my sociological one.

    The unknown is very motivating in science. Anyway , hope this doesn't pollute this blog.

  14. Hey, jpcotter.

    Frankly, I was struck more by the "woo-woooo!!" of Adams' hypothesis. But I agree that the unknown is a great motivator.

    As you're not a spammer and haven't made repeated insults or threats, I don't think you need to be concerned with being a "polluter".

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