The following essay is reprinted with permission from The Conversation, an online publication covering the latest research.
As ships resume the search for missing Malaysian Airlines flight MH370 in the depths of the Indian Ocean this week, we often hear that the oceans are “95% unexplored” and that we know more about the surface of the Moon or Mars than the ocean floor. But is that true, and what do we really mean by “explored”?
The entire ocean floor has now been mapped to a maximum resolution of around 5km, which means we can see most features larger than 5km across in those maps. That’s the resolution of a new global map of the seafloor published recently by David Sandwell of Scripps Institute of Oceanography in San Diego and colleagues, who used some nifty tricks with satellites to estimate the landscape of the sea floor and even reveal some features of the Earth’s crust lurking beneath sea-floor sediments.
Unlike mapping the land, we can’t measure the landscape of the sea floor directly from satellites using radar, because sea water blocks those radio waves. But satellites can use radar to measure the height of the sea’s surface very accurately. And if there are enough measurements to subtract the effects of waves and tides, satellites can actually measure bumps and dips in the sea surface that result from the underlying landscape of the ocean floor.
Where there’s a large underwater mountain or ridge, for example, the tiny local increase in gravity resulting from its mass pulls sea water into a slight bump above it. If instead there is an ocean trench, the weaker local gravity produces a comparative dip in the ocean surface.
Reading those bumps and dips in the sea’s surface is an astounding feat of precision measurement, involving lasers to track the trajectory of the measuring satellite and inevitably a lot of maths to process the data. The new map uses data from the Cryosat-2 and Jason-1 satellites and shows features not seen in earlier maps using data from older satellites. The previous global map of the ocean floor, created using the same techniques and published in 1997, had a resolution of about 20km.
So we do actually have a map of 100% of the ocean floor to a resolution of around 5km. From that, we can see the main features of its hidden landscape, such as the mid-ocean ridges and ocean trenches – and, in that sense, the ocean floor is certainly not “95% unexplored”. But that global map of the ocean floor is admittedly less detailed than maps of Mars, the Moon, or Venus, because of our planet’s watery veil.
NASA’s Magellan spacecraft mapped 98% of the surface of Venus to a resolution of around 100 meters. The entire Martian surface has also been mapped at that resolution and just over 60% of the Red Planet has now been mapped at around 20m resolution. Meanwhile, selenographers have mapped all of the lunar surface at around 100 meter resolution and now even at seven meter resolution.
To map the ocean floor back home in greater detail, we have to use sonar instead of satellites. Modern sonar systems aboard ships can map the ocean floor to a resolution of around 100 meters across a narrow strip below the ship. Those more detailed maps now cover about 10%-15% of the oceans, an area roughly the size of Africa.
Mapping from ships at the level of detail achievable by ship’s sonar systems still reveals plenty of surprises. The first phase of searching for Malaysian Airlines flight MH370 in the Indian Ocean, which involved mapping from ships to plan future surveys by underwater vehicles, found underwater mountains and other features that were not shown on satellite-derived maps for the area.
But if we want to detect things just a few meters in size on the ocean floor, such as the wreckage of missing aircraft or the mineral spires of undersea volcanic vents that my team investigates, we need to take our sonar systems much closer to the sea bed using underwater vehicles or towed instruments. So far, less than 0.05% of the ocean floor has been mapped to that highest level of detail by sonar, which is an area roughly equivalent in size to Tasmania.
And of course, actually to see the sea floor using cameras or our own eyes means getting even closer, using remotely operated vehicles or manned submersibles.
So the “95% unexplored” meme doesn’t really tell the full story of our exploration of the oceans. When it comes to having a large-scale map, the ocean floor is perhaps not as unexplored as we might think, with 100% coverage to a resolution of 5km and 10%-15% coverage at around 100m resolution. That 10%-15% is similar in resolution to the current global maps of Mars and Venus.
But our exploration of the oceans depends on what we want to know about them. If our questions are: “What does it look like down there?” or: “What’s going on down there?”, then the area that has been “explored” is arguably even less than the 0.05% mapped so far at the very highest resolution by sonar.
Philosophically, when it comes to exploring anywhere on our dynamic world, how and when do we decide that somewhere has “been explored”? Do we declare “mission accomplished” once we’ve seen a location for the first time? The local woods where I walk my dog look very different in winter compared with summer, with different species flourishing at different times. Should I have considered them “explored” after my first visit in just one season? Exploring our world starts with mapping, but perhaps doesn’t really have an end.
Jon Copley receives funding from the Natural Environment Research Council.
This article was originally published at The Conversation. Read the original article.
To obtain a better perception of earth's oceans and to understand earth's water cycle.
In earlier grades, students learn about weather, oceans, and water as separate entities. As early as kindergarten, students complete exercises such as measuring and keeping track of precipitation. In grades 3-5, students learn that water can change states: liquid water can evaporate and become a gas, and water vapor becomes liquid due to temperature changes.
This lesson starts to bring the concepts mentioned above together with a focus on the water cycle. The two-fold lesson begins with an experiment that demonstrates water evaporating and coming back down. The lesson is meant to give students a general understanding of earth's oceans. In the end, students should realize that water in the ocean evaporates into the atmosphere and comes back down as precipitation. This lesson is a good introduction to future lessons on weather and earth's climatic changes. (See the extension or the Science NetLinks lesson entitled El Nino.)
Note: Regarding the water cycle, students may have a difficult time understanding the existence of water they cannot see with their own eyes. They may think that evaporated water ceases to exist, or that it can only change into a form they can see, such as fog. (Benchmarks for Science Literacy,p.336.)
For younger students, consider having each one create a book on oceans instead of keeping a journal. As the lesson progresses, students can put each part of the lesson on a separate piece of construction paper. Where the lesson calls for diagrams, students can use paints and magic markers. At the end, have students make a cover page, then three hole punch and tie the "chapters" together.
Older students will keep a journal (or book) with two to three page sections—one section for each task. You may want to recommend that each section of the lesson start on a new journal page with a title at the top.
The following activity, called Build a Model of the Water Cycle, can be found on the Oceans Alive website.
Introduce the lesson with a question: "Do you think there is always the same amount of water in the oceans?" Write down students’ answers on the board.
Now tell students they will set up an experiment that might help them answer the question. If some students understand that water evaporates from the oceans, this experiment will be a good review for them. Divide your class into groups of four or five and provde each group with the Build a Model of the Water Cycle activity sheet. Each group should do their own experiment. Have each group read the whole activity and follow the procedure up to step four. Students should document the procedure and temperature of the water in their journals.
At this point, ask students if they think the water in the baggies will always be the same amount. Discuss this and have students predict what the outcome of the experiment will be. Have students document their predictions in their journals. You will need to wait a few hours before the water in the baggies starts to condense. If necessary, you can revisit the baggies the next day. Tell students to leave room in their journals for observations and conclusions.
Give students a short creative writing assignment. They will have fifteen minutes to write an essay that describes the journey of a drop of water. Tell students they can write in the first person as if they are the drop themselves, or in third person. Encourage students to be creative—the drop of water can exist anywhere and could feasibly travel anywhere, but students should try to describe how.
Once the essays are finished, have students put them aside. Students will have an opportunity to revise their drafts at the end of the lesson and input them into their journals.
Have students observe the baggies and talk about and record their observations. They also should write up a conclusion.
The Water Cycle
To bring the water cycle into the bigger picture, students should use their Oceans student esheet to go to and read: Looking at the Sea: The Water Cycle. In their journals, they should draw their own diagrams of the water cycle, similar to the one at this website. They also should write a paragraph in their own words to describe the water cycle. Ask students to describe how the water cycle is similar to the baggie experiment.
Fact Sheet on Oceans
Students should not only become aware of the water cycle, but also where most of the water on earth is located. Have students develop a fact sheet on oceans. They can develop this page as they use their esheet to go to and read the information at Looking at the Sea.
Getting to Know the Oceans
Now students should go to Looking at the Sea:Ocean Profiles. Instruct them to draw a very basic flat map of earth in their journals as seen on this page. They can shade in the land and label the oceans.
Once the maps are drawn, students should make four ocean profiles in their journals. They may want to use one page to profile two oceans. They can obtain information by clicking on the different areas of the online map to read about the oceans. The profiles should include ocean depths. Tell students to translate the depths into miles by dividing the number of feet by 5,280. (1 mile = 5,280 feet)
Are the Oceans Deep or Shallow?
This question presents a paradox. Though some parts of earth's oceans are up to seven miles deep, they are also a "relatively thin" layer on earth's surface. In question two, students recorded some depths of the oceans. Here, they will diagram earth as a whole, and show that oceans are part of the thin surface layer.
Have students go to Welcome to our Earth, part of the Franklin Institute website. Using this site as a reference, they should draw a diagram of the earth split open, labeling the different layers (crust, mantle, outer core, and core). They also should label how many miles thick each layer is. When they are finished, discuss the fact that oceans are only on the top layer, and that just in comparison to the mantle which is 1,750 miles thick, the ocean may not seem so deep after all.
If time allows, lead a discussion about whether or not the oceans are deep. Some students may refer to the number of miles down an ocean floor is, others may look at the big picture.
Tell each student to write his or her ideas on the page next to the diagram they have just drawn.
What Does the Ocean Floor Look Like?
Students will learn that the ocean floor is a rough terrain of volcanoes, plateaus, and trenches. Have students draw their own ocean floor across the bottom of at least two pages in their journals. In the upper portions of the pages, they can write about some of the land features and describe them.
Students can read about the ocean floor and see a diagram of it at Looking at the Sea: Physical Features of the Ocean.
Currents in the Oceans
Students will probably first think of waves when contemplating movement in the oceans, but they also should learn about currents in order to understand that the atmosphere above affects movement in the oceans. Later they will learn that these currents affect weather patterns.
Have students go to Water on the Move to read the first page. After reading this page, they should click on Current Events to read a little more and see the patterns of currents.
When they are done reading, have them draw the warm and cold currents on the ocean maps they drew earlier in the lesson. Ask them to describe in their journals what causes currents.
Give students an opportunity to write a second draft of their essay, the journey of a water drop. They can use their journals as inspiration. What they have learned should come out in their writing. Encourage them to make the second draft more descriptive and longer. It may be a good homework assignment.
You can collect the journals to evaluate how your students responded to the assigned tasks throughout their journals. The essays should also demonstrate what sort of understanding students have gained from this lesson. Since the assignment is the "journey" of a water drop… the water must get caught in a current, evaporate, and precipitate, or even travel to the depths of the ocean.
A further exploration of the site "Oceans Alive" will broaden the scope of your students' understanding of the oceans. Here are some highlights:
Water Currents: A hands-on activity on currents that demonstrates the differences in temperature and density playing an important role in shaping the ocean currents.
Wind and Waves: A hands-on activity on waves. This activity shows that an object on a body of water with waves will not be moved laterally by the waves, but in a circular motion.
Can sunlight reach the bottom of the ocean? Not the deepest parts. Have students go to The Living Sea to learn about the zones of the ocean and what life forms are found in each zone. Students could add this to their journals by drawing the zone and illustrating some of the life forms.
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