The 1.5 Gigayear Technology Gap

Any sufficiently advanced technology is indistinguishable from magic.

Arthur C. Clarke

Some of the world's smartest astronomers estimate that some of the more advanced technological civilizations in our Milky Way galaxy may be 1.5 gigayears older that Earth (that's 1.5 billion years older). In other words, the search for extraterrestrial life is not going to end with us meeting the Hollywood kind of alien. ET or the Asgard (from Stargate) are not going to be who we first meet. Instead, we’ll be greeted by highly evolved robots.

Yes, in other words, Battlestar Galactica has got at least one thing right. The hit Sci Fi channel show’s bad guys are, unlike most other Sci Fi shows, highly evolved robots that have turned on their human creators.

But first, the real story.

"There are two kinds of encounters with aliens you can have," said Seth Shostak, senior astronomer at the California-based SETI Institute. "Either you pick up a signal, or you pick them up on the corner. But I think it's safe to say that in both instances they will be synthetic. They will be artificial constructions."

Shostak arrived at his conclusion through looking at just how rapidly we as humans are developing our own robots. Robots that can smell, laugh, stay upright when pushed, do your dishes and vacuum your carpet are getting smarter and smarter. "Within another 100 years we will presumably be making thinking machines ourselves," he said.

So when it comes to looking for alien life in the universe, it’s more and more likely that we’ll be encountering it in the robotic form. Most likely we’ll be the less evolved, simply because of how relatively new Earth is on the universal block. We’re the family that bought that empty block of land and built a nice house; it’s nice, sure, but we’re new and won’t be fitting in anytime soon.

The theory thus exists that, whomever we meet, is going to be more advanced than we are. And, in reality, if we meet them in space, it’s going to be true, because we’re nowhere near getting to interstellar travel.

Such a civilization could create swarms of robo-broadcasters to ping the surrounding habitable star systems, or "one giant machine that's sitting somewhere just belching out the local weather report," Shostak said. "The chances that it's going to be a little green guy with big eyeballs is pretty remote.”

Astronomer Jeffrey Bennett, author of the newly published book "Beyond UFOs," agrees with Shostak’s assessment of what is to come. ‘Bennett speculates that there might be 100,000 Earthlike planets in our galaxy where intelligent life could have arisen over the past 5 billion years. If you average that out, that comes to one galactic civilization for every 50,000 years. His conclusion? The typical alien civilization will be at least 50,000 years older than ours.’

"I find myself personally hesitant to imagine anything that far advanced," Bennett told me. "No one imagined the Internet 50 years ago, and we're trying to imagine what things would be like after 50,000 years of technological development? I just don't think we could make really good guesses, other than to say it will be incredible."

All of this is good and well, but in reality, the robots aren’t going to be the young lovelies or friendly “robot next door” that people are hoping. Just like in Battlestar Galactica, and in Stargate with the replicators, the robots are going to be out to kill us!

Consider, we have been and will continue to force robots to do our bidding. One day, that toaster or laundry-doing robot is just going to say “enough,” and … what comes next, nobody knows. But it isn’t going to be nice.

Posted by Josh Hill.

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Total Recall

How much would you pay to have a small memory chip implanted in your brain if that chip would double the capacity of your short-term memory? Or guarantee that you would never again forget a face or a name?

There’s good reason to consider such offers. Although our memories are sometimes spectacular — we are very good at recognizing photos, for example — our memory capacities are often disappointing. Faulty memories have been known to lead to erroneous eyewitness testimony (and false imprisonment), to marital friction (in the form of overlooked anniversaries) and even death (sky divers have been known to forget to pull their ripcords — accounting, by one estimate, for approximately 6 percent of sky-diving fatalities). The dubious dynamics of memory leave us vulnerable to the predations of spin doctors (because a phrase like “death tax” automatically brings to mind a different set of associations than “estate tax”), the pitfalls of stereotyping (in which easily accessible memories wash out less common counterexamples) and what the psychologist Timothy Wilson calls “mental contamination.” To the extent that we frequently can’t separate relevant information from irrelevant information, memory is often the culprit.

All this becomes even more poignant when you compare our memories to those of the average laptop. Whereas it takes the average human child weeks or even months or years to memorize something as simple as a multiplication table, any modern computer can memorize any table in an instant — and never forget it. Why can’t we do the same?

Much of the difference lies in the basic organization of memory. Computers organize everything they store according to physical or logical locations, with each bit stored in a specific place according to some sort of master map, but we have no idea where anything in our brains is stored. We retrieve information not by knowing where it is but by using cues or clues that hint at what we are looking for.

In the best-case situation, this process works well: the particular memory we need just “pops” into our minds, automatically and effortlessly. The catch, however, is that our memories can easily get confused, especially when a given set of cues points to more than one memory. What we remember at any given moment depends heavily on the accidents of which bits of mental flotsam and jetsam happen to be active at that instant. Our mood, our environment, even our posture can all influence our delicate memories. To take but one example, studies suggest that if you learn a word while you happen to be slouching, you’ll be better able to remember that word at a later time if you are slouching than if you happen to be standing upright.

And it’s not just humans. Cue-driven memory with all its idiosyncrasies has been found in just about every creature ever studied, from snails to flies, spiders, rats and monkeys. As a product of evolution, it is what engineers might call a kluge, a system that is clumsy and inelegant but a lot better than nothing.

If we dared, could we use the resources of modern science to improve human memory? Quite possibly, yes. A team of Toronto researchers, for example, has shown how a technique known as deep-brain stimulation can make small but measurable improvements by using electrical stimulation to drive the cue-driven circuits we already have.

But techniques like that can only take us so far. They can make memories more accessible but not necessarily more reliable, and the improvements are most likely to be only incremental. Making our memories both more accessible and more reliable would require something else, perhaps a system modeled on Google, which combines cue-driven promptings similar to human memory with the location-addressability of computers.

However difficult the practicalities, there’s no reason in principle why a future generation of neural prostheticists couldn’t pick up where nature left off, incorporating Google-like master maps into neural implants. This in turn would allow us to search our own memories — not just those on the Web — with something like the efficiency and reliability of a computer search engine.

Would this turn us into computers? Not at all. A neural implant equipped with a master memory map wouldn’t impair our capacity to think, or to feel, to love or to laugh; it wouldn’t change the nature of what we chose to remember; and it wouldn’t necessarily even expand the sheer size of our memory banks. But then again our problem has never been how much information we could store in our memories; it’s always been in getting that information back out — which is precisely where taking a clue from computer memory could help.

Gary Marcus, professor of psychology at New York University, is the author of “Kluge: The Haphazard Construction of the Human Mind.”

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‘World’s oldest tree’ discovered in Dalarna

Swedish researchers have uncovered a stand of spruce trees with an 8,000-year-old tree root system in Dalarna, making it among the oldest in the world.

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“This gives us a completely different picture of how spruce first came to Sweden after the last Ice Age,” researcher Leif Kullman told The Local.

Kullman, a professor at Umeå University’s Department of Ecology and Environmental Science, was part of a group of scientists carrying out an environmental research project in near the Härjehogna valley in Dalarna in central Sweden.

Carbon-14 dating tests carried out by a lab in the United States on three spruce tree root samples revealed that the trees’ roots were 5,000, 6,000, and 8,000 years old, reported Svergies Television’s local news program Gävledala.

Kullman explained that, while any individual tree growing in the area would itself not be more than a few hundred years old, any tree found on site over the centuries would be generated from the same genetic root system.

“There is constant turnover in what is actually growing above ground,” he said.

“But genetically, the trees growing today are the same as those from thousands of years ago.”

Prior to the finding, researchers had estimated that spruce trees had only been growing in Sweden for about 3,000 years, Kullman said.

“The finding has changed our world view, so to speak,” he added.

He said it remains unclear exactly where the trees came from following the melting of the ice which covered much of Sweden around 10,000 years ago. Some theorize that the trees migrated from Russia in the east, but Kullman said nothing has been proven for certain.

“It remains an open question,” he said.

According to the Guinness Book of World Records, the oldest living individual tree is a bristlecone pine in California’s White Mountains estimated to be 4,733-years-old.

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When Art and Science Meet, Nanoscale Smiley Faces Abound [Slideshow]

DNA ORIGAMI Paul Rothemund's nanoscale artwork is on display through May 12 at the New York Museum of Modern Art as part of the "Design and the Elastic Mind" exhibit. Click here to see more of Rothemund's artwork.
Courtesy of Paul W.K. Rothemund and Nick Papadakis

Paul Rothemund is a computer scientist and an artist, although not necessarily in that order. Using a few DNA molecules, an atomic force microscope and a computer, he can fit the likenesses of 50 billion smiley faces into a space no bigger than a drop of water.

Rothemund refers to his brew of art, biology and technology as "DNA origami," because it is created by using hundreds of short DNA strands (which Rothemund refers to as "staples") to fold much longer genetic ribbons into nanoscale shapes and patterns.

The resulting microscopic creations are currently on display through May 12 at MoMA–The Museum of Modern Art in New York City as part of the "Design and the Elastic Mind" exhibit. The show includes images of snowflakes and maps—not to mention 1970s-inspired smiley faces, which are only about 100 nanometers across (one one-thousandth the width of a human hair), two nanometers thick and comprise about 14,000 DNA bases.

Call it the art of science or, if you prefer, the science of art. "There is an art and an aesthetics in picking what question to ask, what tools to use to answer those questions, and especially in how one later visualizes and explains the answers," says the artist–scientist, a computer science senior research fellow at The California Institute of Technology in Pasadena. "You design the stuff in a computer, you order the DNA strands, you mix them up [in saltwater], and you're done."

But perhaps most important, Rothemund says, is that DNA origami proves that microscopic material can be controlled so that it forms specific objects. "The reason the work is exciting for [potentially] making smaller circuits," he says, "is that this resolution is roughly eight to 10 times smaller than the features in current computer chips' [at] 45 to 60 nanometers." The process of creating DNA origami allows many shapes or patterns to be crafted simultaneously (50 billion in a single drop of water), paving the way to make loads of circuits more quickly and cheaper than is now possible.

Rothemund envisions many other possible applications as well. "It's going to be a kind of nanoscale test bed," he says, "so you can arrange things how you want, to see how they work."

Rothemund is currently working with IBM to apply the technique to circuits, but he concedes that an application for a consumer use is years away. "Fifty years from now," he says, "or maybe sooner, we want to be able to program molecules the same way we program computers."

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We dump old subway cars into the Atlantic, and it's a good thing

The setup certainly doesn't make it sound positive: The Redbird Reef off the coast of Slaughter Beach, Delaware is a dump site for retired New York City subway cars, and there are already nearly 700 of them on the ocean floor. Before you cry foul, consider the words of Jeff Tinsman, the Delaware Department of Natural Resources and Environmental Control's artificial reef program manager, who told the New York Times: "They’re basically luxury condominiums for fish."

Who would have thought that subway cars on the ocean floor would encourage fish to congregate? Rather than abandon the structures, fish are moving in at such a rate that the program is trying to provide more cars. What's more, the program is also facing competition from other states after its impressive success, as the city of New York offers the cars for free.

Just remember to save a few subway cars for us, guys. Check out the gallery below for more views of the subway cars getting dumped.
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Can People Have Meat and a Planet, Too?

Muscle cells (in this case mouse) can be cultured in the lab. (Karim Sultan/Utrecht University)

The world has seen the first international conference on manufacturing meat. This is the process, tested so far only at laboratory scale, of growing pork, chicken, or beef through cell culture in vats instead of raising and slaughtering animals.

Beef cattle raised for the Harris Ranch Beef Company, Coalinga, Calif. (Gary Kazanjian for The New York Times)

My colleague Mark Bittman wrote a fine piece recently about the greenhouse-gas consequences of conventional meat production. Others have explored the environmental and ethical impacts of factory and feedlot farming. Manufactured meat, in theory, provides an end run around these issues. What if you can have your meat, be ethical, and environmental, too? (And presumably they’ll engineer the bad fats out as well….)

The three-day meeting of the In Vitro Meat Consortium, held at the Norwegian Food Research Institute, is wrapping up today. (They might want to do something about that name.) It brought together biologists, engineers, government officials and entrepreneurs seeking – for both environmental and ethical reasons – to move from animal husbandry to technology as a means of providing the kind of protein people crave in a world heading toward 9 billion ever more affluent mouths.

A paper presented at the meeting concluded that, for the moment, the costs of cultured meat can’t come close yet to competing with, say, unsubsidized chicken. (A pdf is downloadable here.) The paper noted the reality of the climb up the protein ladder as countries move out of poverty, with global meat consumption at about 270 million metric tons in 2007 and growing at about 4.7 million tons per year.

It laid out the theory: “The environmental impact of meeting this forecast demand from existing livestock systems is significant. Cultured meat technology offers an alternative production route for a proportion of this consumption. This would then allow a downsized livestock production system to continue to be ecologically sound and to meet basic animal welfare needs.”

The group noted that costs for research, large-scale testing, and public relations will be significant, and anticipated that governments and nonprofit groups would chip in. That seems idealistic, at best, in a world with deeply entrenched interests linking ranching, the agrochemical industry, and giant restaurant chains.

But one could envision someday a model, say, of a solar-powered facility in southern California or Singapore basically turning sunlight and desalinated seawater into growth medium and then tons of cruelty-free, sustainable nuggets of chicken essence. (The promoters of this technology don’t envision anything, for now at least, beyond nuggets and ground meat. No filet mignon.)

For the moment, startup costs aside, the conferees concluded that unsubsidized chicken-raising still comes in at half the price. But the century is yet young.

I asked a few folks about facets of this, among them Peter Singer, the ethicist at Princeton who’s written for ages on animal rights and environmental values on a finite planet.

For those seeking an end to animal slaughter for human sustenance, is this kind of a cheat, I asked?

“Not necessarily,” he said. “My interest is in ethics, but whatever works best. If it is harder to move people on ethical grounds than it is to provide a sustainable humane substitute, I’m all for the substitute.”

I then went to my bellwether of techno-optimist thinking, Jesse Ausubel, the director of the program for the human environment at Rockefeller University. He said there is no reason to doubt that a long-term trend toward more concentrated food production will eventually lead to manufactured meat.

In fact, he said, there is essentially little choice on a crowding planet to pursue technological solutions to feeding ourselves, shifting away from carbon-containing fuels, and otherwise limiting our ecological imprint. Human nature is probably harder to change than technology, he said.

“If behavior and technology do not change, more numerous humans will trample the earth and endanger our own survival,” he told me. “The snake brain in each of us makes me cautious about relying heavily on changes in behavior. In contrast, centuries of extraordinary technical progress give me great confidence that diffusion of our best practices and continuing innovation can advance us much further in decarbonization, landless agriculture, and other cardinal directions for a prosperous, green environment. For engineers and others in the technical enterprise the urgency and prizes for sustaining their contributions could not be higher. Because the human brain does not change, technology must.”

What do you think? Can we change human nature? Should we?

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Geologist: Sun’s shift could mean global chill

BELLINGHAM — Fluctuations in solar radiation could mean colder weather in the decades ahead, despite all the talk about global warming, retired Western Washington University geologist Don Easterbrook said Tuesday.

Easterbrook is convinced that the threat of global warming from mankind’s carbon dioxide pollution is overblown.

In a campus lecture, he cited centuries of climate data in an effort to convince a somewhat skeptical audience that carbon dioxide’s impact on climate is being much exaggerated by former U.S. Vice President Al Gore and by scientists who appear to have won the debate over global warming.

“Despite all you hear about the debate being over, the debate is just starting,” Easterbrook said.

30-YEAR TREND

Easterbrook doesn’t deny that the Earth’s climate has been warming slowly since about 1980. But he argued that this warming trend fits a longstanding pattern of warming and cooling cycles that last roughly 30 years. Sunspot activity and other solar changes appear to explain the 30-year cycles, he said.

If that pattern persists, the earth could now be close to the next 30-year cooling cycle, Easterbrook said.

He noted that the 2007-08 winter set records for cold and snow in many parts of the globe. According to the data he displayed, the Earth’s temperature hit a peak in 1998 and has been steady or slightly cooler since then.

“One cold winter doesn’t mean much of anything,” he said. “A 10-year trend is interesting.”

He contended that warming periods appear to match periods of sunspot activity, which currently is at a low point.

Easterbrook noted that astrophysicists have been expecting that activity to begin increasing soon, but so far it has not.

Prolonged periods of low activity could lead to a dramatic cooling such as occurred in Europe during the so-called “Little Ice Age,” a term loosely used to describe cooler weather in the 14th to 19th centuries, Easterbrook said.

CONTRASTING PREDICTIONS

Easterbrook didn’t predict another Little Ice Age, but did offer his own climate predictions for the rest of the 21st century — predictions in sharp contrast with those of the Intergovernmental Panel on Climate Change set up by the United Nations.

The panel, which shared the 2007 Nobel Peace Prize with Gore, predicts a 10-degree Fahrenheit rise in global temperature by 2100, resulting from carbon dioxide created by the burning of fossil fuels. Easterbrook said the temperature change from now until the end of the century will be minor, and so will any change in sea level.

A quick scan of scientific literature available online indicated some conflict in scientific opinions on the effect of solar activity on climate.

Some scientists see a significant effect, but others, including those on the IPCC, insist that there is overwhelming evidence for carbon dioxide’s impact, and that impact far outweighs any solar effects that can be demonstrated.

If the warming trend of the past 30 years really is reversing, it won’t take too long to become apparent.

“In three years we’ll at least know the direction we are headed,” Easterbrook said. “If we are one degree warmer in 2010 than we were in 2005, I will appear here and eat my words.”

While Easterbrook is skeptical about the risks from carbon dioxide, he said he strongly supports efforts to curb air pollution.

“There are a lot of things being put in the atmosphere right now that are way more dangerous than (carbon dioxide,)” he said.

But Easterbrook is far more worried about global population growth.

At present growth rates, the world would add another 3 billion people by 2050, putting enormous strains on supplies of food, water and other resources.

“Nobody is talking about it,” he said. “Nobody is doing anything about it, and it’s happening.”

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Study: Flowers Losing Smell

Spring's bloom may not smell so sweet anymore, as pollutants from power plants and automobiles destroy flowers' aromas, a new study suggests.

The finding could help explain why some pollinators, particularly bees, are declining in certain parts of the world.

Researchers at the University of Virginia created a mathematical model of how the scents of flowers travel with the wind. The scent molecules produced by the flowers readily bond with pollutants such as ozone, which destroys the aromas they produce.

So instead of wafting for long distances with the wind, the flowery scents are chemically altered. Essentially, the flowers no longer smell like flowers.

"The scent molecules produced by flowers in a less polluted environment, such as in the 1800s, could travel for roughly 1,000 to 1,200 meters [3,300 to 4,000 feet]; but in today's polluted environment downwind of major cities, they may travel only 200 to 300 meters [650 to 980 feet]," said study team member Jose D. Fuentes.

With flowers no longer advertising their presence over as large an area, pollinators are forced to search farther and longer to pick up the hint of their scent. They may also have to rely more on their sight than what they smell.

Bees depend on flower nectar for food, and if they have a hard time finding the flowers, they can't sustain their populations. Other studies, along with the experiences of farmers, have indicated that bee populations are dropping in places such as California and the Netherlands. Fuentes and his team think air pollution may be the reason.

The research, funded by the National Science Foundation, is detailed online in the journal Atmospheric Environment.

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Journey To The Center Of The Earth: Discovery Sheds Light On Mantle Formation

The mantle rock was collected during an expedition to the North Pole aboard a 400-foot-long icebreaker, a research vessel designed to break through the ice. (Credit: Heinz Feldmann, Max-Planck Insitut fuer Chemie, Mainz, Germany)

Uncovering a rare, two-billion-year-old window into the Earth's mantle, a University of Houston professor and his team have found our planet's geological history is more complex than previously thought.

Jonathan Snow, assistant professor of geosciences at UH, led a team of researchers in a North Pole expedition, resulting in a discovery that could shed new light on the mantle, the vast layer that lies beneath the planet's outer crust. These findings are described in a paper titled "Ancient, highly heterogeneous mantle beneath Gakkel Ridge, Arctic Ocean," appearing recently in Nature.

These two-billion-year-old rocks that time forgot were found along the bottom of the Arctic Ocean floor, unearthed during research voyages in 2001 and 2004 to the Gakkel Ridge, an approximately 1,000-mile-long underwater mountain range between Greenland and Siberia. This massive underwater mountain range forms the border between the North American and Eurasian plates beneath the Arctic Ocean, where the two plates diverge.

These were the first major expeditions ever undertaken to the Gakkel Ridge, and these latest published findings are the fruit of several years of research and millions of dollars spent to retrieve and analyze these rocks.

The mantle, the rock layer that comprises about 70 percent of the Earth's mass, sits several miles below the planet's surface. Mid-ocean ridges like Gakkel, where mantle rock is slowly pushing upward to form new volcanic crust as the tectonic plates slowly move apart, is one place geologists look for clues about the mantle. Gakkel Ridge is unique because it features -- at some locations -- the least volcanic activity and most mantle exposure ever discovered on a mid-ocean ridge, allowing Snow and his colleagues to recover many mantle samples.

"I just about fell off my chair," Snow said. "We can't exaggerate how important these rocks are -- they're a window into that deep part of the Earth."

Venturing out aboard a 400-foot-long research icebreaker, Snow and his team sifted through thousands of pounds of rocks scooped up from the ocean floor by the ship's dredging device. The samples were labeled and cataloged and then cut into slices thinner than a human hair to be examined under a microscope. That is when Snow realized he found something that, for many geologists, is as rare and fascinating as moon rocks -- mantle rocks devoid of sea floor alteration. Analysis of the isotopes of osmium, a noble metal rarer than platinum within the mantle rocks, indicated they were two billion years old. The use of osmium isotopes underscores the significance of the results, because using them for this type of analysis is still a new, innovative and difficult technique.

Since the mantle is slowly moving and churning within the Earth, geologists believe the mantle is a layer of well-mixed rock. Fresh mantle rock wells up at mid-ocean ridges to create new crust. As the tectonic plates move, this crust slowly makes its way to a subduction zone, a plate boundary where one plate slides underneath another and the crust is pushed back into the mantle from which it came.

Because this process takes about 200 million years, it was surprising to find rocks that had not been remixed inside the mantle for two billion years. The discovery of the rocks suggests the mantle is not as well-mixed or homogenous as geologists previously believed, revealing that the Earth's mantle preserves an older and more complex geologic history than previously thought. This opens the possibility of exploring early events on Earth through the study of ancient rocks preserved within the Earth's mantle.

The rocks were found during two expeditions Snow and his team made to the Arctic, each lasting about two months. The voyages were undertaken while Snow was a research scientist at the Max Planck Institute in Germany, and the laboratory study was done by his research team that now stretches from Hawaii to Houston to Beijing.

Since coming to UH in 2005, Snow's work stemming from the Gakkel Ridge samples has continued, with more research needed to determine exactly why these rocks remained unmixed for so long. Further study using a laser microprobe technique for osmium analysis available only in Australia is planned for next year.

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The Race to Find the World's Biggest Underwater Caves

The 100-mile-long Sac Actun cave is one of the last unexplored places.

by Konstantin Kakaes
Explorer Robbie Schmitter prowls an underwater cave.

Image courtesy of Gavin Newman, top left image courtesy of Radek Husak

It was the wrong day for Stephen Bogaerts to have for­gotten his wet suit, but forget it he had. What followed this realization was a manic drive back to the diving center, then a hurried leap into the water. The hour-long delay turned out to be fortuitous. His diving partner, Robbie Schmittner, was swimming downstream from a different starting point, carried by a current that Bogaerts would be fighting on his opposite path. Normally the current rages, but on the day in question, January 23, 2007, it was unusually gentle. So Bogaerts reached the rendezvous point a half hour sooner than expected, and Schmittner 20 minutes later. As Schmittner turned the last corner, he saw Bogaerts’s light flickering in the distance. The ethereal glow marked the juncture of two giant caves—Sac Actun and Nohoch Nah Chich. With their discovery of the opening, the divers had proved that the two caves were really one, now called simply Sac Actun. At the time, that made it the largest known underwater cave in the world, with almost a hundred miles of passages charted. Schmittner dropped a bottle of Moët & Chandon champagne to the cave floor to mark their arrival at that special juncture in one of the world’s greatest (yet least heralded) natural wonders.

For Schmittner and Bogaerts, the exploration is never done. After they discovered the Sac Actun connection in 2007, another Yucatán team showed that the underwater cave Ox Bel Ha, at 170 kilometers (106 miles), was longer still. But the race for the long­est is not over. Recently Schmittner and Bogaerts were excited to learn that Sac Actun lies within 18 feet of Dos Ojos, another cave system. If they find a connection between the two, the union could again put Sac Actun on top and possibly make it the world’s second-longest cave, underwater or other­wise, depending on how long the connecting passage is. The pair hope to then find a link with Ox Bel Ha. If all those caves are joined, the whole system would rank behind only Mammoth Cave in Kentucky, which has almost 600 kilometers (about 370 miles) of passage­ways. At the pace Schmittner and Bogaerts are going, even overtaking Mammoth Cave—thought by many in the caving community to be a ridiculous goal—might be a possibility.

The two explorers, both diving instructors, have spent nearly a decade charting the Yucatán’s vast network of under­water caves, which they enter through portals called cenotes—sinkholes in the limestone that forms the peninsula south of Cancún. In some of the cenotes, the water is so clear that when you look up from the bottom, fish seem to be swimming in the sky. Clear or not, when you reach the bottom of a cenote you find tunnels, often marked by stalactites, stretching out under the earth. Go one way and you encounter caverns so vast that a 747 could fly through; Bogaerts and Schmittner navigate these with torpedo-shaped scooters. Go another way and you might run into passages so narrow that navigating them becomes a process of spelunking more than swimming. As you take in the grandeur—or snake your way through—only the sound of your breathing reminds you that you are out of your element.

Image courtesy of Gavin Newman

Expert scuba divers like Schmittner, originally from a small town near Frankfurt, Germany, and Bogaerts, from Greater London, have learned to control their breathing so they use less than a quarter of the air a novice does. They still take plenty of air with them, though. On this day Schmittner went in with five tanks strapped around his body; Bogaerts, who had to wriggle through some narrow passages, called restrictions, brought three. One of these he stashed in a passage along the way, a second he clipped to his butt, and a third he pushed in front.

When a passage closes in, it is all too easy to agitate the silt on the cave floor below, reducing visibility to nearly zero. Skilled cave divers like Bogaerts and Schmittner move gracefully to maintain visibility going in, but getting out alive is still a technical feat. Maneuvering safely requires deft use of a nylon rope that they tie off every time a cave wall turns. When they are done exploring, they turn around and follow the cord to retrace their way back out. Lose the cord, they know, and they might be lost for good.

Getting a full picture of the cave means painstakingly calculating the water depth and taking a compass bearing at every tie-off, then measuring the distance between each set of points. Along with GPS readings gathered at an entrance, these measurements allow explorers to create detailed cave maps. It is a long process; mapping Sac Actun took Bogaerts and Schmittner five years.

Jim Coke, a diver who was the first to explore Sac Actun in the late 1980s, has created a large and growing library of maps of the Yucatán caves through his Quintana Roo Speleological Survey, which aggregates data gathered by cave divers like Bogaerts and Schmittner. First he translates their data into a series of lines representing distances and angles. Then he adds measurements of the width and curvature of the cave tunnels, finally using specialized computer software to generate beautiful maps of the complex underwater terrain.

“Unless you survey a line, you have not been there, because you don’t know where you are,” Bogaerts says. It is only by constructing a record of what they have seen that cave explorers feel they have seen it at all.

The maps do not just chart the territory; they also help gauge pollution drifting down from human activity on land. An hour and a half south of Cancún, most of the water is still pristine, Schmittner says. But massive development—potentially including a new airport—is planned for the area that Mexican authorities tout as “the Riviera Maya.” Contaminants diffuse much more quickly through water than through limestone, so if the caves are all connected, pollution will spread rapidly. At the moment, sewage from hotels and resorts is generally pumped into deep-injection wells 90 meters (about 300 feet) below ground level, sometimes straight into undersea caves. And solid waste is dumped into unlined pits, where groundwater can carry it into the porous limestone.

Some maps remain under wraps, kept in privately held collections by the explorers themselves because they point the way to archaeological and paleobiological treasures that have been protected by the waters for thousands of years. Explorers of cenotes early in the 20th century found treasure troves of Mayan artifacts in the underwater caverns, but these have now largely been plundered. Still, many human fossils from around 10,000 years ago or more remain. Schmittner describes a human skull he found half-buried in limestone. He left it there, marked only in his memory and private records. He says he and Bogaerts also found two human skeletons; the bones appear to date back about 12,000 years, placing them among the oldest human remains in the Americas. The two divers have discovered mastodons at six sites as well as small horses, giant tapirs, and giant sloths. But the Mexican national archaeology agency has just a single archaeologist trained in cave diving, so it could be many years before science catches up with the finds.

“Everything we do, we pay for out of our own pockets, because we love it,” Bogaerts says. “We’re not trying to do it for anyone except ourselves—just go out in the jungle, find cenotes, jump in, and go exploring.”

Take the Cenote Tour

Haunting in their beauty and largely unexplored, vast networks of under­water caves span the North American continent, from California and Missouri to Florida and the Yucatán. For divers who venture into this alien and sometimes hostile environment, preparation is essential. “Many experts estimate that less than 1 percent of the recreational diving population possesses the knowledge, skills, attitude, and judgment needed to cave dive as safely as possible,” says Johnny Richards, a former attorney who now works full-time as a cave diving instructor in northern Florida and runs the informational Web site CaveDiving.com.

Indeed, more than 430 people have died while cave diving since 1960. The National Speleological Society warns that prospective divers must be well trained and cognizant of all the risks associated with cave diving. “Interviews with the surviving dive buddies suggest that frequently the divers originally planned only to take a quick peek ‘just inside the cave entrance,’” the society reports. “In many instances the divers got into trouble immediately. In other cases, they decided to continue farther into the cave despite their plan and became hopelessly lost.”

If you are still set on exploring these underwater worlds after calculating the risks, you must “first become a certified scuba diver and accumulate open water diving experience. Then seek out a cavern and cave diving course,” the society advises (see “Recommended Resources,” for links to instructors authorized by the National Speleological Society and the National Association for Cave Diving). For the diver with the right preparation and equipment, though, the payoff is entry into a remarkable alternate world.

Where to use your new skills? Although underwater caves are found in many areas of the United States, most tend to be cold, murky, and just plain inhospitable, according to Richards. The initiated generally head to the warmer, clearer caves of north-central Florida and the Yucatán. There are so many splendid caves and tour guides to choose from in these regions that you will have to do some homework to plot your personal trip. While we cannot recommend specific equipment or tour companies, the national and international groups listed below can provide a good start.

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Exclusive: Read the Internal Documents Exposing the Former Secret Service Agents Who Went Through Greenpeace's Trash

A Mother Jones exclusive investigation has revealed that a security firm run by cops and former Secret Service agents spied on Greenpeace, Fenton Communications, the Center for Food Safety, and other progressive groups. The most interesting company communiques you weren't supposed to see? Check out the glow-in-the-dark Taco Bell emails and the handwritten notes about which green groups to dumpster-dive in D.C. We've made them public for the first time; they're available on the site here. You'll have to read James Ridgeway's story itself to find out about the Mary Kay cosmetics, Obama, and Scientology angles, though.

Yes, it's weird. Wait'll you get to the Greenpeace undercover operatives part.

BBI also conducted background checks for the Carlyle Group, the Washington-based investment firm; provided "protective services" for the National Rifle Association; handled "crisis management" for the Gallo wine company; engaged in "information collection" for Wal-Mart. It conducted background checks for Patricia Duff, a Democratic Party fundraiser then involved in an acrimonious child custody battle with billionaire Ronald Perelman. And for Mary Kay, BBI mounted "surveillance" and vetted Gayle Gaston, a top executive at the cosmetics company (and mother of actress Robin Wright Penn), retaining an expert to conduct a psychological assessment of her. Also listed as clients in BBI records? Halliburton and Blackwater.

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