Earth may have underground ‘ocean’ three times that on surface

After decades of searching scientists have discovered that a vast reservoir of water, enough to fill the Earth’s oceans three times over, may be trapped hundreds of miles beneath the surface, potentially transforming our understanding of how the planet was formed.

The water is locked up in a mineral called ringwoodite about 660km (400 miles) beneath the crust of the Earth, researchers say. Geophysicist Steve Jacobsen from Northwestern University in the US co-authored the studypublished in the journal Science and said the discovery suggested Earth’s water may have come from within, driven to the surface by geological activity, rather than being deposited by icy comets hitting the forming planet as held by the prevailing theories.

“Geological processes on the Earth’s surface, such as earthquakes or erupting volcanoes, are an expression of what is going on inside the Earth, out of our sight,” Jacobsen said.

“I think we are finally seeing evidence for a whole-Earth water cycle, which may help explain the vast amount of liquid water on the surface of our habitable planet. Scientists have been looking for this missing deep water for decades.”

Jacobsen and his colleagues are the first to provide direct evidence that there may be water in an area of the Earth’s mantle known as the transition zone. They based their findings on a study of a vast underground region extending across most of the interior of the US.

Ringwoodite acts like a sponge due to a crystal structure that makes it attract hydrogen and trap water.

If just 1% of the weight of mantle rock located in the transition zone was water it would be equivalent to nearly three times the amount of water in our oceans, Jacobsen said.

The study used data from the USArray, a network of seismometers across the US that measure the vibrations of earthquakes, combined with Jacobsen’s lab experiments on rocks simulating the high pressures found more than 600km underground.

It produced evidence that melting and movement of rock in the transition zone – hundreds of kilometres down, between the upper and lower mantles – led to a process where water could become fused and trapped in the rock.

The discovery is remarkable because most melting in the mantle was previously thought to occur at a much shallower distance, about 80km below the Earth’s surface.

Jacobsen told the New Scientist that the hidden water might also act as a buffer for the oceans on the surface, explaining why they have stayed the same size for millions of years. “If [the stored water] wasn’t there, it would be on the surface of the Earth, and mountaintops would be the only land poking out,” he said.

Advertisements

The Man Who Speaks For Earth

Recently, at a mass in Vatican City, Pope Francis said that, if given the chance, he would baptize aliens. (“Who are we to close doors?” he asked.) Unfortunately, judging by “Archaeology, Anthropology, and Interstellar Communication,” a new book, about the complexities of communicating with extraterrestrials, released last month by NASA, it won’t be that simple. For a long time, the people most interested in searching for extraterrestrial intelligence came from “hard science” disciplines like astronomy or physics; to them, the main obstacles seemed technical (building radio telescopes, processing signal data). But, in recent years, the field has broadened to include people who already study other civilizations here on Earth. In these essays, they report that their jobs are hard enough as it is. Archaeologists struggled to decipher ancient Greek; deciphering a transmission from another world will be even more difficult. Even if we do manage to detect a signal, they write, fully understanding what it means may be impossible.

The challenges described by the contributors are daunting (and, at least to me, surprising). On Earth, they write, we were able to use the Rosetta Stone to figure out Egyptian hieroglyphics. (It contained the same text written in glyphs, Demotic script, and ancient Greek.) But there will be no Rosetta Stone for our communication with extraterrestrials, and the distances involved make conversation unlikely—which may mean that our comprehension of their message will be confined to math and numbers, never able to make the jump to broader concepts or less abstract words. (How do you describe a lake, or a tree, with math?) The speed of the message presents another problem: here on Earth, human language happens at a speed somewhere between birdsong and whalesong, so how fast should our message be, and on what scale should we be listening? And then there are all the difficulties created by the nature of our interlocutors. What if they’re so different from us that our messages are mutually incomprehensible? What if the message is sent by some sort of automated system—a voicemail from a long-dead civilization?

Douglas Vakoch, the editor of “Archaeology, Anthropology, and Interstellar Communication,” is the director of interstellar message composition at the SETI Institute, in Mountain View, California. (The Institute’s name refers to the “search for extraterrestrial intelligence,” an umbrella term for a number of projects that began in the sixties, some funded by NASA.) Vakoch has degrees in comparative religion, the history and philosophy of science, and clinical psychology (“I expected to become an astronomer, but discovered that I was more interested in people than in stars,” he told me). At SETI, Vakoch is responsible for designing the messages that we might send to extraterrestrials; he is also a member of the International Institute of Space Law, where he works on the policy issues surrounding the messages’ composition. (There are currently no laws about sending signals into space; in theory, anyone with a powerful enough antenna could be talking to the cosmos right now.) “We used to think we would get an Encyclopedia Galactica,” Vakoch said. One of his primary goals, in editing the book, was to give air time to the less optimistic views of social scientists, and to start thinking about what an incomplete or indecipherable message from space might mean to humankind.

Vakoch spoke to me by phone, from his home in California. This interview has been edited and condensed.

TheNewYorker

“Stargate” notwithstanding, when I think of space, archaeologists and anthropologists don’t come to mind. What do they contribute to the SETI effort?

Anthropologists are very familiar with encountering those who are radically other; archaeologists are very good at saying, We have only a fragment of a past civilization, and we’re trying to reconstruct it. Both of those situations will be at the center of communicating with extraterrestrials. When we take seriously the distance between us and any other civilization, we see that we have no easy way to ask a question and get a reply. We don’t even know what language they’re going to be using.

And if we’re thinking of replying, and of getting a reply back, then we have to ask: How do we make sure that, one thousand years from now, future humans will be able to understand that message? Because it’s only at those time scales that it becomes plausible that we’ll begin to understand something.

Your job is to help design the messages we might send to extraterrestrials. What’s the starting point for that work? How do you begin?

There is no obvious starting point, but there are some approaches that are easier than others—for example, mathematics. So then the question is, What are the most fundamental parts of mathematics? Maybe it’s counting. Maybe mathematics as a whole isn’t universal, but if we can start with something fundamental, we can build up to communicating, step by step, our way of bringing order into the universe.

It’s also useful to step back and look at communication more generally. In the early days of SETI there was this idea of “send them information, and make it redundant, and the patterns will be self-evident.” Nowadays, that seems ridiculous. So what’s the alternative? If something like language—whether a natural language like English or Mandarin, or a language like mathematics—if those aren’t universal, maybe we can step back and look at signs in a more general sense. That’s one of the ways in which semiotics has been helpful. Maybe a big accomplishment in communicating with an extraterrestrial is just to convey that there’s something on this end who’s intending to send something. Even if it’s something as rudimentary as sending an index—a message that points toward an astronomical object—or an icon, something that looks like, say, the radiation pattern of hydrogen. Just so they say, “Oh, these are sign-bearing, sign-using creatures—there’s hope.”

Has SETI, or has anyone, actively started broadcasting in a way designed to attract notice?

There have been a few transmissions. There hasn’t been anything sustained, though, and I think there would be real advantages to starting a sustained transmission. That would increase the sense of this being an intergenerational project. It signals our own hopes for humanity—that we hope to be around in one thousand years to get a reply back. We recognize that what we do today is just one step in contact.

One of the most inhibiting aspects of interstellar communications is the sense that, somehow, we need to get everything absolutely right and completely comprehensible the first time out. That’s not how we communicate on Earth.

You’re in favor of transmitting sooner rather than later?

If it turns out that we actually have little hope of understanding a message, how does that affect our search strategies? Maybe it makes sense for us to start transmitting. The way it’s typically been cast in the past is, They’re smarter, and they’ll be better at sending an intelligible message. But the flip side is, if they’re smart, they’ll also be better at decoding an ambiguous message. Maybe they’ll be able to detect, from the form of the message, “This seems to be something we’ve seen from visually oriented species, or auditory-oriented species.” That might be more important.

Let’s suppose that at some point we do make contact, but using these ambiguous, perhaps indecipherable messages. What’s the point of that?

First of all, we have to think, For whose benefit are we sending this message? Is it for our benefit, to say that we existed? To say, Here are values that we have? You could also ask, What would an extraterrestrial want to know? We could say, “We’re wise, we’re strong.” A more interesting message might be, “This is what we’re struggling with; we don’t know if we’re going to exist for another century, or what life will look like on this world then.”

One of the benefits of all this is, we have to reflect on what we want to say, and how we want to say it. We have a Web site called Earth Speaks, where we ask visitors to contribute what they would like to say to an extraterrestrial. We look at the words people use: in comparison to English in general, the world “but” is used one hundred and fifty times more often.

On the other side: in the book, [the philosopher and cognitive scientist] Dominique Lestel talks about the implications of realizing, over the course of millennia, that we really can’t communicate or decipher a message. And he calls it an existential crisis. Because how does that impact our understanding of what we’re doing when we’re doing math, science, philosophy?

It seems like the trend has been toward a more pessimistic outlook, at least as far as interpreting a message is concerned. Are there any optimistic trends?

What you describe as pessimism I would characterize as skeptical and critical. But it’s a criticism that engages, as opposed to a criticism that dismisses. We’re getting closer to understanding, What are the complexities we face? And what are their implications?

One of the big positive developments is that, in the last fifteen years, we’ve learned that there are planets out there. Now we know that almost every star has planets—about one out of five probably has an Earth-like planet in a habitable zone. Knowing where the planets are lets us prioritize those targets in our searches. This actually would have been even more relevant if it had turned out that planets are rare! But the very fact that we’re finding so many—we now know there are roughly Earth-sized planets within the habitable zones of even red dwarfs—that’s a game changer. We know there are places where extraterrestrials could live.

And what if you work at SETI for the rest of your life, doing this work, and you don’t find anything?

There are payoffs to the project that we can be assured are happening, at some level, with some degree of depth. But the greatest outcome—actually making contact with and understanding another civilization—that’s difficult to have any assurance of. So this is a case where the project requires an ability to stand in the unknown. Science is usually associated with values like objectivity and truth, and we want those, too. But one of the values behind SETI is patience.

Illustration by Dadu Shin.

Why haven’t we encountered aliens yet? The answer could be climate change

Enrico Fermi, when asked about intelligent life on other planets, famously replied, “Where are they?” Any civilisation advanced enough to undertake interstellar travel would, he argued, in a brief period of cosmic time, populate its entire galaxy. Yet, we haven’t made any contact with such life. This has become the famous “Fermi Paradox”.

Various explanations for why we don’t see aliens have been proposed – perhaps interstellar travel is impossible or maybe civilisations are always self-destructive. But with every new discovery of a potentially habitable planet, the Fermi Paradox becomes increasingly mysterious. There could be hundreds of millions of potentially habitable worlds in the Milky Way alone.

This impression is only reinforced by the recent discovery of a “Mega-Earth”, a rocky planet 17 times more massive than the Earth but with only a thin atmosphere. Previously, it was thought that worlds this large would hold onto an atmosphere so thick that their surfaces would experience uninhabitable temperatures and pressures. But if this isn’t true, there is a whole new category of potentially habitable real estate in the cosmos.

Finding ET

So why don’t we see advanced civilisations swarming across the universe? One problem may be climate change. It is not that advanced civilisations always destroy themselves by over-heating their biospheres (although that is a possibility). Instead, because stars become brighter as they age, most planets with an initially life-friendly climate will become uninhabitably hot long before intelligent life emerges.

The Earth has had 4 billion years of good weather despite our sun burning a lot more fuel than when Earth was formed. We can estimate the amount of warming this should have produced thanks to the scientific effort to predict the consequences of man-made greenhouse-gas emissions.

These models predict that our planet should warm by a few degrees centigrade for each percentage increase in heating at Earth’s surface. This is roughly the increased heating produced by carbon dioxide at the levels expected for the end of the 21st century. (Incidentally, that is where the IPCCprediction of global warming of around 3°C centigrade comes from.)

Over the past half-billion years, a time period for which we have reasonable records of Earth’s climate, the sun’s surface temperature increased by 4% and terrestrial temperatures should have risen by roughly 10°C. But the geological record shows that, if anything, on average temperatures fell.

Simple extrapolations show that over the whole history of life, temperatures should have risen by almost 100°C. If that were true, early life must have emerged upon a completely frozen planet. Yet, the young Earth had liquid water on its surface. So what’s going on?

Get lucky

The answer is that it us not just the sun that has changed. The Earth also evolved, with the appearance of land plants around 400m years ago changing atmospheric composition and the amount of heat Earth reflects back into space. There has also been geological change with the continental area steadily growing through time as volcanic activity added to the land-mass and this, too, had an effect on the atmosphere and Earth’s reflectivity.

Remarkably, biological and geological evolution have generally produced cooling and this has compensated for the warming effect of our ageing sun. There have been times when compensation was too slow or too fast, and the Earth warmed or cooled, but not once since life first emerged has liquid water completely disappeared from the surface.

Our planet has therefore miraculously moderated climate change for four billion years. This observation led to the development of the Gaia hypothesis that a complex biosphere automatically regulates the environment in its own interests. However, Gaia lacks a credible mechanism and has probably confused cause and effect: a reasonably stable environment is a precondition for a complex biosphere not the other way around.

Other inhabited planets in the universe must also have found ways to prevent global warming. Watery worlds suitable for life will have climates that, like the Earth, are highly sensitive to changing circumstances. The repeated cancelling of star-induced warming by “geobiological” cooling, required to keep such planets habitable, will have needed many coincidences and the vast majority of such planets will have run out of luck long before sentient beings evolved.

However, the universe is immense and a few rare worlds will have had the necessary good fortune. It may just be that Earth is one of those lucky planets – a precious, fragile jewel in space. So, perhaps inevitably, climate change will remain a bane of the continued existence of life on such planets.