"She eyes me like a pisces when I am weak
I've been locked inside your Heart Shaped box for weeks
I've been drawn into your magnet tar pit trap
I wish I could eat your cancer when you turn black" -Nirvana, Heart-Shaped Box
By looking at the right combinations of wavelengths of light, one can literally find almost anything in the depths of space.
Image credit: Daniel Marquardt, of nebula IC 1805.
But back on Earth, we have some surprising natural features that have been captured from above with nothing more than a camera.
Image credit: NASA / STS-129 / Space Shuttle Atlantis, retrieved from ruscosmos.narod.ru.
The International Space Station completes an orbit of the entire Earth every 90 minutes or so, moving along at a clip of around 25,000 kilometers an hour. Because of the capabilities of the cameras on board, it can find never-before-seen areas of both the continents and the oceans.
And I bet you've never seen a photo of Earth like this one.
Image credit: NASA / ESA, taken by Paolo Nespoli.
You might be wondering to yourself just how on Earth something like this came to be. It's not a cloud; it's not a stunt-plane trail.
It's known as an atoll, and they're found interspersed throughout the oceans on Earth. Here, have another.
Image credit: Image Science and Analysis Laboratory, NASA-Johnson Space Center.
So where do these atolls -- found almost exclusively in the Pacific and Indian Oceans -- come from? Believe it or not, it all starts with a volcano, and not just anywhere, but at the bottom of the ocean!
Image credit: Pacific Marine Environmental Laboratory / NOAA.
At many different locations on the sea floor, liquid magma from deep within the Earth's mantle rises up through the crust, emerging from below. The molten rock enters the Ocean waters -- typically at about 4° Celsius -- at temperature up to 1200° Celsius! And you can very easily imagine exactly what happens. On one hand, the lava emerging into the ocean immediately heats up and boils off large quantities of water, for as long as the eruption takes place!
But on the other hand, what happens to the rock? Being much denser than water, after the initial eruption, it cools and sinks down to the bottom of the ocean, flowing down to as low a point as possible. It's this very process that's going on off of the coast of the Canary Islands right now, at El Hierro.
Image credit: New El Hierro volcano crater and Lava Flow, courtesy of ieo.es.
Over a long enough time period of continued, successive eruptions, the cooled lava forms a conical structure, reaching closer to sea level and the atmosphere above it.
Image credit: Zina Deretsky, National Science Foundation.
When the undersea cone is built up high enough, lava eruptions can pierce through the interface between the ocean and the atmosphere -- for the first time -- and when it cools, it can begin to create land. This is how, perhaps most famously, all of Hawaii was created! In fact, it's still being created, as Hawaii's Kilauea first surfaced above the Ocean just 23,000 years ago, and its seamount Loihi will do so just a few thousand years into the future!
Image credit: T.J. Takahashi and USGS.
Once the lava flow ceases and this volcanic cone becomes extinct, you'll find yourself left with a relatively stable Oceanic island. From this point, two important things -- one of which is unavoidable and the other which requires the right conditions -- happen.
The one that requires the right conditions is that, on the sides of this mountain, beneath the surface of the water, a fringing coral reef begins to form. It can take up to 10,000 years for a fringing reef to form, but if it does, what happens next is truly amazing. Coral is one of the most slowly growing features, made up of individual organisms (polyps) that are mere milimeters in size. Over time periods on the order of 100,000 years, if conditions are right, the reef grows in size, outwards, in the shallow waters around the island.
Image credit: Maldives Coral Islands, retrieved from designswan.com.
The island itself, however, whether it successfully grows a large coral reef or not, will erode over time. A combination of wind, the ocean, and weather will, over geologically long time periods, wear the island itself away. Oftentimes, what looks like the rim of a crater will be the last piece of land to survive before the entire island is weathered away.
Image credit: Molokini Crater, retrieved from hawaiiweathertoday.com.
But while the island weathers away, if it happens to have a fringing reef that's grown outwards around it, the coral is quite capable of growing downwards as well, to keep up with the ever-submerging island. While coral reefs thrive just a few meters beneath the surface, some coral organisms can survive down to depths of 3,000 meters, or nearly 10,000 feet! What usually winds up happening is the coastline shrinks away from the coral, which in turn continues to grow outwards into the ocean beyond. When you get a separation between the coast of an eroding shore and the coral reef that grows out into the ocean, that's called a barrier reef!
Image credit: New Caledonia Barrier Reef, retrieved from designswan.com.
But while it may take 100,000 years or more for a great coral reef like this to form, it may take up to -- wait for it -- 30 million years for the island to erode completely away!
When it does, the coral continues to grown downwards to remain anchored to the mountain beneath it, maintaining its shallow depths just barely beneath the ocean's surface. That final stage, where a large, circular coral reef simply encloses an empty, landless lagoon, is what forms an atoll!
Image credit: NOAA.
And that's what you're looking at when you see the heart-shaped object captured by the ISS at the top, as well as at the Atafu atoll, in Tokelau, below.
Image credit: NASA / Johnson Space Center.
The culmination of over a hundred thousand years of organism growth underwater, followed by millions of years of erosion of a once-proud island, is what it takes to create these beautiful and elusive sights.
Perhaps what's even more amazing is that this story -- the accepted theory on the formation of these atolls -- dates back to none other than Charles Darwin!
Image screen-captured from wikipedia.
So remember, astronomy isn't only amazing when we look up; sometimes there's great joy, beauty, and science in remembering to look down, too!
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Thanks.
Really good summary, a lot that I didn't know, particularly how long it takes for reefs to grow.
I don't blame you for not mentioning climate change. But discussion of coral reefs isn't complete without mentioning climate change.
"Climate change, pollution, crown-of-thorns starfish and fishing are the primary threats to the health of this reef system.... The Great Barrier Reef Marine Park Authority considers the greatest threat to the Great Barrier Reef to be climate change, causing ocean warming which increases coral bleaching. Mass coral bleaching events due to elevated ocean temperatures occurred in the summers of 1998, 2002 and 2006, and coral bleaching is expected to become an annual occurrence." Wiki
Since all the anti-climate folks are busy fighting on Ethan's previous posts and since no one else has said anything on this excellent post let me help bring the crowd here.
"Major storms could submerge New York City in next decade... Irene-like storms of the future would put a third of New York City streets under water and flood many of the tunnels leading into Manhattan in under an hour because of climate change, a new state government report warns Wednesday... Subway tunnels get affected, airports - both LaGuardia and Kennedy sit right at sea level - and when you are talking about the lowest areas of the city you are talking about the business districts... The report, commisioned by the New York State Energy Research and Development Authority, said the effects of sea level rise and changing weather patterns would be felt as early as the next decade." http://www.guardian.co.uk/environment/2011/nov/16/climate-change-report…
I'm a little off topic because no one is claiming that Manhattan will become an atoll.
Quoting more "New York mayor Michael Bloomberg... commissioned an even more detailed study of the city after receiving early briefings on the report... That makes him an outlier among his fellow Republicans, who blocked funds for creating a new climate service in budget negotiations in Congress this week."
We need coral reefs and we need business districts of major cities.
I know I'm getting a bit carried away. But this is also too interesting not to plug.
"Mongolia bids to keep city cool with 'ice shield' experiment. Geoengineering trial aims to 'store' winter temperatures in a giant block of ice that will cool and water Ulan Bator in summer... "Everyone is panicking about melting glaciers and icecaps, but nobody has yet found a cheap, environmentally friendly alternative... If you know how to manipulate them, naled ice shields can repair permafrost and building cool parks in cities." " http://www.guardian.co.uk/environment/2011/nov/15/mongolia-ice-shield-g…
OK that's enough to bring the crowd to this post.
Hope you learn some science.
Anybody know what nebula that is in the first picture?
You left out an important piece of information. In addition to being weathered down to sea level, the island also sinks. On many atolls, the basalt core is now thousands of feet below the surface, this can't happen by weathering. As the oceanic plate on which the island sits moves away from the spreading center, it cools and shrinks. This is slow process, but eventually takes the island below sea level. In most cases it is also more rapid than weathering.
Though Darwin was basically correct about how atolls form, he didn't know about plate tectonics. What goes down can also come up. There are atolls that are elevated well above sea level due to tectonic processes. These elevated atolls turned out to be valuable resources when it was found that they often have large phosphate deposits on their uplifted plateaus.