A Confluence of Holidays
This year, there's an interesting calendrical coincidence: Today is both Earth Day and Good Friday. That being so, I thought it would prove enlightening to compare these two holidays and the messages they respectively send to their practitioners.
One of the holidays on this date is to commemorate the gory death of a Jewish mystic some two thousand years ago, a dimly remembered event in an obscure corner of a long-vanished empire - an event which, we're told, takes precedence over everything else that's ever happened, and that people living today should feel personally responsible for. The other is to celebrate the Earth - our home, the cradle of our life - and to remind us of its vulnerability and our common responsibility to protect it.
In many ways, these holidays sum up the competing religious and secular views of our existence, and the contrast between them couldn't be clearer. One celebrates parochial interests; the other is for the sake of common concerns that matter to all of us. One is to pay homage to superstition; the other is to raise awareness of the pressing realities we can't afford to ignore. One holiday is meant to fill us with misery and lamentation; the other is meant to give us reason to hope. One holiday is meant to keep us dwelling on the past; the other encourages us to look to the future.
The overwhelming importance placed by Christians on Good Friday, its ad nauseam repetition and commemoration, shows the myopia of their religious viewpoint. Even if Jesus existed, his death was just one among many in a turbulent and violent era, yet believers continue to insist that this one death, out of billions of anonymous and forgotten others in human history, is freighted with cosmic significance. Some go so far as to call it the only truly important thing that's ever happened in the entire lifetime of the cosmos, and its consequences the only thing worth concerning ourselves with.
Meanwhile, Earth Day calls our attention not to provincial religious mythologies, but to a broader, global perspective and to the things of true importance that are happening on our planet. In the real world, rainforest is being cut down to grow cash crops and graze cattle, and the green and living lungs of the planet are slowly turning to desert. In the real world, our reckless burning of fossil fuel continues to pump carbon into the atmosphere, and as the climate slowly warms in response, ice caps and glaciers are retreating, droughts are growing more severe and storms more powerful, and sea levels are rising, threatening island nations and coastal cities alike. In the real world, human overuse and sprawl is draining aquifers, drying up lakes and rivers, ransacking virgin habitat, and driving species to extinction, each one a unique, irreplaceable treasure trove of genetic diversity lost forever.
These realities press in on us, whether we want to admit it or not. Try as we might to adapt, they're undermining the way of life our civilization has grown to depend on. If we continue on our unsustainable course, there will come a day when we'll have to face a reckoning - and no ancient, crucified Jewish sage is going to return from the clouds to magically save us all by recreating the Earth as it once was. Hoping for a miracle is only going to distract us from the urgency of the course corrections we still have to make, while there's time for them to do our descendants any good.
Not only does Good Friday value superstition over reality, its intent is to moor believers to the past, perpetually replaying a long-ago evil - and telling them that they are personally responsible for it. In the Roman Catholic tradition, Good Friday is a day of lamentation, penance and sorrow. Believers are encouraged to fast all day, to perform the Stations of the Cross (a series of images used to visualize and meditate on Jesus' agonizing death), and to pray acts of reparation apologizing for the crucifixion. Church altars are covered with black cloth, and in some churches, images of the crucified Jesus or Jesus in the tomb are presented so that believers can kneel, weep and kiss them. Any display of happiness is frowned on. According to the official Catholic liturgy, even funerals held on this day should have no singing or music.
By contrast, Earth Day calls on us to acknowledge our responsibility in environmental destruction, yes, but not for the sake of self-flagellation. Rather, its purpose is to inspire us to mindfulness and action: to preserve what hasn't been destroyed, to save what can still be saved, to avert what can still be averted, and most of all, to do this not out of guilt but because we recognize our world as a precious thing worthy of protection. Our planet is a vast, ineffably beautiful, majestic yet fragile place, unique (as far as we know) in all the immensity of the cosmos, and its riches and wonders are the common property of humankind. We should learn from it not to exalt one faith, one culture, or one life above all others, because we are all part of an interconnected whole, and it's this recognition, and not baseless superstition, that should guide us to a more enlightened and moral view of our place in it all.
[Editor's Note: As an Earth Day treat, check out NASA's Eyes on the Earth website - a stunning multimedia display that lets you track, in real time, the scientific satellites orbiting our planet, see them up close, learn about their missions, and even see the data that they've collected!]
Is There Life on Mars and Venus?
You may have heard that the scientific community is buzzing with excitement over the discovery of Gliese 581g, an Earth-sized planet circling the red dwarf star Gliese 581, 20 light-years from Earth in the constellation Libra. Five other planets orbiting this star were already known, but what's exciting is that the new one is smack in the middle of the star's habitable zone, making it the best candidate ever discovered for an extrasolar planet with liquid water. And where water flows, is it possible that life follows?
This finding is a major blow to the creationists who insist that Earth must be the only life-supporting planet that exists. As the scientists who discovered Gliese 581g pointed out, finding a habitable planet this easily means that we've either been incredibly lucky, or such planets are common.
But I wanted to turn my attention a little closer to home for the moment. You might think, given the effort scientists are putting into finding Earth-like planets beyond the solar system, that we've exhausted all possibilities for discovering alien life any closer to home. Surprisingly, not only is that far from the truth, we have evidence which could imply the existence of life dwelling on our very nearest planetary neighbors.
Take Venus. Despite being Earthlike in size and composition, Venus has a surface of crushing pressure and 900-degree temperatures, making it almost certain that no life could survive - on the surface. But the surface isn't the only environment on the planet where life could conceivably exist. The planetary scientist David Grinspoon, in a daring feat of imagination, hypothesized that free-floating microbial life could exist in Venus' atmosphere. In the upper reaches of the Venusian atmosphere, the temperature is a far more hospitable 80 degrees, with the same pressure as Earth, and some evidence even suggests the presence of water. It's possible that life began on Venus' surface billions of years ago, but as the steadily increasing greenhouse effect turned the surface into an inferno, it escaped into the atmosphere, drifting high above the killing heat.
And this hypothesis isn't pure speculation. There's some tantalizing evidence which could indicate the presence of life in Venus' clouds.
The astrobiologists Dirk Schulze-Makuch and Louis Irwin pointed out that Venus' atmosphere contains very little carbon monoxide. This is curious, because lightning and ultraviolet radiation should be producing this gas in large amounts. Even more suggestively, Venus' atmosphere contains significant amounts of three other molecules - hydrogen sulfide, sulfur dioxide, and carbonyl sulfide - which, at least on Earth, are only produced by life or by volcanic activity. Venus does have active volcanoes, but not as many as Earth (since it has no plate tectonics), and it's not certain whether it's enough to account for the measured abundances. It's possible that some as-yet-unknown chemical pathway is breaking down carbon monoxide and producing these other compounds. But it's also possible that what we see in our spectroscopes is the metabolic signature of Venusian life, drifting in the planet's clouds and thriving to such an extent as to alter the balance of its atmosphere.
Mars has been explored much more thoroughly than Venus, and it too has given evidence to tantalize us. The two Viking spacecraft which landed on Mars in the 1970s carried experiments designed to test for the presence of life. The most surprising of these was the so-called labeled release experiment, which added water and nutrients to a sample of Martian soil. The nutrients were "tagged" with radioactive carbon-14, and the assumption was that, if there were microbes in the soil, they would metabolize them and release radioactive carbon dioxide gas. And when the experiment was run, the carbon dioxide was indeed detected. Even more excitingly, when the experiment was repeated after heating the soil to sterilizing temperatures, no gas was detected - as if any microorganisms in the soil had been killed off.
However, Viking's gas chromatograph found no evidence of organic compounds in the soil. That seemed to be the death knell for possible life - until, in 2008, NASA's Phoenix lander discovered a compound called perchlorate in Martian soil. Perchlorate becomes a strong oxidizing agent when heated, as the gas chromatograph does, and some scientists feel that this would have rapidly broken down any organic molecules and would explain why they didn't show up in the analysis. The evidence from the Viking experiments is still much-debated and ambiguous, but it certainly doesn't rule out the possibility of life.
Also, like Venus, Mars has anomalous chemical compounds in its atmosphere: in this case methane, which was detected by the European Space Agency's Mars Express spacecraft. This molecule would rapidly decompose under Martian conditions, so for it to exist there means that something must be continually replenishing it. As with the anomalous compounds on Venus, it could be released by volcanic activity - except that Mars has no known volcanism, and is believed to be geologically dead. It's possible that the methane is being produced by a geologic process called serpentinization. But it's also possible that Mars is home to methanogenic bacteria, producing the gas as a product of their metabolism. Most likely, Martian methanogens would live far below the surface, deep underground where it's warmer and there may be liquid water - similar to archaea on Earth that live in similar conditions deep within the crust.
The idea of life existing on either or both of these planets shouldn't be too surprising. Although Venus is a suffocating inferno and Mars a freezing dry desert, both planets had clement pasts with surfaces where liquid water flowed. Both these planets, during the formation of the solar system, presumably received organic molecules from the same source as Earth's. Depending on your assumptions about how likely abiogenesis is, life could well have started on all three planets at about the same time. We won't know for sure, of course, until we've had a more detailed look - but it's worth remembering that even the nearest shores of our vast and awesome cosmos may yet contain marvels we haven't dreamed of.
The Case for a Creator: A Universe Not Made For Us
The Case for a Creator, Chapter 7
The final section of this chapter concerns Gonzalez's argument that the Earth is uniquely designed to make scientific discovery possible. His argument is that our planet is fine-tuned not just to allow the existence of life, but to allow us to find out important facts about the nature of the universe that wouldn't be possible to discover if we lived anywhere else. (As an aside, it's asinine for Strobel and his interviewees to celebrate how perfectly designed the Earth is for scientific discovery when they themselves reject many of the most important conclusions of science - but never mind that.) He begins with solar eclipses, which occur due to another of those coincidences that ID advocates love so much:
"There's a striking convergence of rare properties that allow people on Earth to witness perfect solar eclipses... total eclipses are possible because the sun is four hundred times larger than the moon, but it's also four hundred times further away. It's that incredible coincidence that creates a perfect match.
Because of this configuration... observers on earth can discern finer details in the sun's chromosphere and corona than from any other planet, which makes these eclipses scientifically rich." [p.185-186]
Again, this is something that Guillermo Gonzalez, a professional astronomer, can't possibly be ignorant of: You don't need a solar eclipse to view the sun's corona. You can just use a coronagraph, a very simple instrument that's been in existence since the 1930s and performs the same function. The fact that our planet is uniquely positioned to see total eclipses is an interesting coincidence, but it's in no way vital to scientific discovery.
"...perfect solar eclipses helped us learn about the nature of stars. Using spectroscopes, astronomers learned how the sun's color spectrum is produced, and that data helped them later interpret the spectra of distant stars." [p.186]
This argument makes no sense to me. What do eclipses have to do with humanity's invention of spectroscopy?
"...eclipses provided a historical record that has... enabled us to put ancient calendars on our modern calendar system, which was very significant." [p.186]
Eclipses, of course, are not the only way of coordinating ancient and modern calendars. You can use any event, whether earthly or astronomical, that occurred on a known date as a reference point. SN 1054 would be another example.
"Our location away from the galaxy's center and in the flat plane of the disk provides us with a particularly privileged vantage point for observing both nearby and distant stars." [p.187]
Wouldn't a location in a more densely populated stellar neighborhood give us an even better vantage point for observing many different types of stars? This is a Gish Gallop-type argument where Gonzalez fires out as many assertions as possible, while doing little or nothing to explain the reasoning behind each one.
"The moon stabilizes the Earth's tilt, which gives us a livable climate - and it also consistently preserves the deep snow deposits in the polar regions... By taking core samples from the ice, researchers can gather data going back hundreds of thousands of years." [p.187]
I agree that ice-core data is a useful way of learning about past climate, though not the only one. I also note that Gonzalez has here committed himself to rejecting the young-earth position, which is something Strobel refuses to do (he calls it an "internal Christian debate", remember). It's therefore interesting that he lets this pass without comment. Shouldn't he point out that, according to many of his fellow Christians, the Earth doesn't have "hundreds of thousands of years" of past history and therefore these ice cores are useless as records of anything?
"And a transparent atmosphere allows the science of astronomy and cosmology to flourish." [p.188]
This argument is especially ridiculous. Every atmosphere, no matter its composition, is transparent at some wavelengths and opaque at others. Our atmosphere, for example, is transparent to visible light but strongly absorbs infrared. Astronomers on any planet would ply their trade at the wavelengths that pass through the atmosphere, and for those that don't, they could do precisely what we've done: send telescopes and observatories into space.
"Thousands of seismographs all over the planet have measured earthquakes through the years... scientists have been able to use that data to produce a three-dimensional map of the structure of the Earth's interior." [p.188]
The same effect can be achieved by setting off explosives on the surface to produce seismic waves, a technique used routinely by geologists and the extraction industry.
As we can see from all these examples, there's nothing about the Earth's environment that makes it uniquely well-suited to scientific discovery. What Strobel and Gonzalez have really managed to show, instead, is humanity's cleverness in exploiting every opportunity available to us to learn about the natural world. Our planet is well-suited for science in some ways, ill-suited in others. If we lived on a different planet, the ways we'd have to learn about the world would be different - and if there were creationists on that planet, doubtless they'd be saying that those opportunities, and not these, were evidence of divine design.
As evidence of this, Strobel and Gonzalez have presented a rosy and thoroughly one-sided list of the ways in which our environment is good for scientific discovery. But there are other aspects of our environment, equally obvious and important, that are not so favorable. Here are some of them:
* The light speed limit. The fact that nothing can travel faster than light makes it essentially impossible to explore our universe in person, or even via robots. Even the nearest stars would take thousands of years to reach using the fastest means of travel currently available to us, and exploring any really interesting places, like the galactic center, would take millions.
* The poor fossil record. Because fossilization is an extremely rare event, most creatures, and possibly even most species, that have ever lived are unknown to us. Even in the very rare cases where fossils are formed, we need to rely on luck to bring them close enough to the surface to notice, and incredible amounts of tenacity and hard work are needed to excavate even a single fossil and assemble it from fragments and disassembled bones.
* Erosion and plate tectonics. The active geological processes that continually destroy and recycle the Earth's crust mean that most of the planet's oldest rocks and fossils no longer exist, making it very difficult for us to learn about the earliest epochs of history.
* Dark matter, dark energy, and other elusive phenomena. To judge by astronomical observations, the vast majority of the universe is made up of substances that are invisible to us and completely unlike anything we encounter on our planet. Enormous amounts of research, creativity, and effort have been expended in building the vast and complex experiments that we use to detect them (just read this description of the Cryogenic Dark Matter Search experiment, or this page about the Large Hadron Collider).
* Geological and cosmological timescales. Many really interesting scientific phenomena - continental drift, star formation, galaxy collisions - occur on such long timescales that they can't be directly observed from start to finish by humans and our comparatively puny lifespans. This is very inconvenient for learning about the processes that shape our planet and our universe.
These aspects of our world (are there others I've forgotten?) cast doubt on the rats-in-a-maze theology which claims our universe is stocked with little puzzles created by God just to keep us busy. Nature does not yield its secrets easily, and the few pieces of knowledge we've managed to gain have all taken diligent work and imaginative leaps by dedicated scientists. It trivializes and demeans their effort for creationists to come in afterward and claim that those scientists were really just finding the clues planted by God.
Other posts in this series:
The Case for a Creator: Hot Jupiters
The Case for a Creator, Chapter 7
In chapter 3, I chastised Jonathan Wells, a trained biologist, for making deceptive arguments whose answers he unquestionably already knows. I have to send a similar criticism Guillermo Gonzalez's way, because in this chapter, he makes an argument that any beginner student in astronomy would be able to answer easily.
The argument has to do with the nature of extrasolar planets, of which we currently know over 400. Gonzalez concedes that this means our solar system is not unique when it comes to having planets orbiting a star - a point he's clearly reluctant to yield - but he still maintains that what we have discovered reinforces his claim about the uniqueness of Earth.
"...the expectation was that astronomers would find giant gas planets in large circular orbits, much like Jupiter... However, we're finding that the planets circling other stars are quite different from Jupiter. They orbit over a full range of distances, from just a tiny fraction of an Astronomical Unit - which is the distance between the Earth and the sun - out to several Astronomical Units. Most of their orbits are highly elliptical; very few are circular. These strongly non-circular orbits utterly surprised astronomers... they had expected that other planetary systems would be just like ours. And that expectation was basically dashed." [p.173]
Strobel lets this comment pass without asking for any examples of astronomers who had allegedly expected this. I doubt he would have gotten any if he had.
It's true that most of the extrasolar planets we've found so far are "hot Jupiters", or gas giants with orbits that take them very close to their parent stars. (Most hot Jupiters do, in fact, have circular orbits, so Gonzalez is wrong on that point.) But that's not because every extrasolar planet is like that. Rather, it's because the detection methods we use are most sensitive to this type of planet.
One of the most successful ways of detecting extrasolar planets is the radial-velocity method. As a massive planet orbits its star, the gravity of the planet tugs the star back and forth. This causes a small, but detectable, Doppler shift in the frequency of the star's light as observed from Earth. Because gravity is proportional to mass and inversely proportional to distance, the planets with the largest gravitational effects on their parent stars - the ones that are easiest to detect - are very large and orbit very close: in other words, hot Jupiters.
Planet-finding instruments like HARPS have astounding sensitivity, able to detect velocity shifts in stars as small as 1 m/s. But even they aren't sensitive enough to detect the minuscule Doppler shifts that Earth-size planets would cause. Finding terrestrial exoplanets will have to wait for next-generation instruments like NASA's Terrestrial Planet Finder mission - although, as our methods improve, we're finding more and more exoplanets in a category called super-Earths - rocky worlds much smaller than gas giants, but with up to ten times the mass of our own planet.
Searching for these planets is like sweeping the ocean with a net to catch fish. The more finely-woven your net, the smaller the fish you'll be able to catch. Our "net" is still fairly coarse, able to catch only the larger fish. Strobel and his creationist allies would claim that this proves that only large fish live in the ocean. But we're getting better at weaving finer and finer nets, and every year we're catching smaller and smaller fish. This is an area where the science is progressing very rapidly, and we're in the very rare position of being able to know, possibly within just a few years, exactly how wrong the creationists are.
Having spent all this time discussing religious pseudoscience, I just have to cleanse my palate now by talking about some real science, especially since there's such an abundance to be had. Feast your eyes on the first ever visible-light image of a planet outside our solar system:
This composite image, taken by the Hubble Space Telescope's Advanced Camera for Surveys, shows a dust disk surrounding the bright star Fomalhaut (see also), about 25 light-years from Earth in the constellation Piscis Australis. The star itself has been blocked out from the image, so that its light doesn't drown out the far dimmer object orbiting it: the planet named Fomalhaut b, which is about the same mass as Jupiter and orbits its parent once every 872 years, four times as far as Neptune is from our own sun.
Fomalhaut is a young, hot white star, similar to Vega and Sirius. It's only about 200 million years old - which means Fomalhaut b must be similarly young - but is expected to burn for no more than another billion years or so. The star is surrounded by a vast disk of dust, which very likely resembles the one that coalesced into the planets of our own solar system. Fomalhaut b's gravity has shepherded the particles of this disk, which accounts for the relatively sharp inner edge visible in the Hubble photo. The disk also radiates strongly in the infrared, which may indicate heat being radiated from the collision of small rocky bodies and planetesimals - implying that planet formation may be occurring around Fomalhaut, or even that other young planets exist within this system that have yet to be observed.
One more intriguing fact is that Fomalhaut b is significantly brighter than expected for a planet of its mass. A possible explanation is that the planet, like Saturn, has a ring system that reflects starlight (though, one of the scientists who theorized this said that its rings could dwarf Saturn's by comparison).
These are the kind of discoveries that creationists wave off, insisting that there's nothing new or interesting worth finding beyond our own world. A worldview that already has all the answers has no place for curiosity. But the universe is greater than they imagine, and every day, real scientists are making discoveries that further reveal to us our true place in the cosmos. There are countless worlds waiting to be explored. Who knows what wonders may yet lie hidden on those other shores?
Other posts in this series:
The Case for a Creator: A Parade of Horribles, Part II
The Case for a Creator, Chapter 7
Gonzalez's next assertion strikes me as highly dubious. He claims that, if the Earth were larger than it is, the higher surface gravity would tend to smooth out mountains and ocean basins, producing a perfectly spherical planet with little surface relief. (He provides no numbers on how much bigger the planet could be before this happens.) This would result in a "water world" whose surface was evenly covered by a shallow ocean, and "a water world is a dead world" [p.181] because there would be no continental weathering to wash mineral nutrients into the oceans. "In a water world, many of the life-essential minerals would sink to the bottom. That's the basic problem." [p.181]
Yet again, evolution is smarter than the creationists. Vital minerals sinking to the ocean bottom would suit hydrothermal vent communities just fine - the ocean-bottom ecosystems that use minerals spewing from volcanic fissures in the ocean floor and subsist on chemical energy rather than sunlight. Some biologists even believe that these "black smokers" are where life on Earth began.
"Besides, the salt concentration in a water world would be prohibitively high. Life can only tolerate a certain level of saltiness." [p.181]
Gonzalez's argument here is that in continental environments like marshes, ocean water can evaporate and leave salt deposits behind, preventing the seas from becoming too salty, but this couldn't happen in a water world.
This reminds me of those young-earth creationist lists that offer various "proofs" which directly oppose each other. One of my favorites was the list that claimed, on the one hand, that the Earth must be young because if it was old, erosion would have worn away all the mountains, and on the other hand, the Earth must be young because if it was old, volcanism would have created mountains much higher and larger than we see today.
Gonzalez, allegedly a scientific authority, has made the same elementary blunder here. Salt comes from continents! If we lived on a water world, with no continents to erode and wash material into the ocean, there would be no source of salt. And, yet again, Gonzalez overlooks the fact that some species of Earthlife already can cope with the very salty environments that he claims would make life impossible. They are called halophiles. The green alga Dunaliella salina, for example, can live in water with a 30% salt content (ocean water is about 3% salt).
Next on the list is plate tectonics, which Gonzalez claims is a necessary ingredient for life. The book correctly describes the cause: the natural heat of radioactivity, which keeps the earth's interior hot and causes the continental plates to drift on an underlying sea of semi-molten rock. The churning of the Earth's iron core also creates a dynamo effect that's responsible for the planet's magnetic field.
"The magnetic field is crucial to life on Earth... If we didn't have a magnetic shield, there would be more dangerous radiation reaching the atmosphere." [p.183]
But every few hundred thousand years, the Earth's magnetic field reverses - in other words, the magnetic north and south poles exchange places. (We know this from the geological record: iron crystals in lava align with the geomagnetic field like tiny compass needles, then are frozen in place when the lava cools and hardens.) A full magnetic reversal takes several thousand years from start to finish, and while it's happening, our planet has a greatly weakened magnetic field. Life has obviously survived these events, and no mass extinctions are known to be correlated with pole reversals.
Gonzalez also says that plate tectonics plays a vital role in the carbon cycle, subducting carbonate minerals into the mantle and then reemitting them from volcanoes as carbon dioxide. This does play a role in creating the environment for life on Earth, but again, there's no reason to believe it's an absolute necessity. Carbon dioxide levels have been much higher in past geological periods, and this too did not lead to the extinction of all life.
The Galactic Habitable Zone
Gonzalez's final assertion has to do with the Earth's location in the galaxy. He says that Earth is located in a "safe area" [p.169] of the Milky Way, far from the central supermassive black hole and from active star-forming regions, both of which would have dangerously high levels of radiation. On the other hand, the galaxy's outer regions and globular clusters are composed mostly of older, cooler stars and lack the heavy elements that are cooked up by supernovae and that are needed to form planets and life:
"...[Y]ou can have a whole globular cluster with hundreds of thousands of stars, and yet there won't be a single Earth." [p.170]
Clearly, Gonzalez has a strong point here. Globular clusters lack heavy elements, are too gravitationally unstable, and in all other ways are completely unsuitable for planets. Therefore, we can't possibly have discovered PSR B1620-26b, an extrasolar planet orbiting a dual-star system in the globular cluster Messier 4.
Now, I'll grant that Gonzalez is not entirely wrong: the low metallicity of globular clusters does make them a poor environment for planetary formation. (Another factor may be the stronger ultraviolet radiation in globular clusters that would dissipate protoplanetary disks of gas and dust.) But the existence of PSR B1620-26b shows that it is not impossible. In fact, not only does this planet exist, it's thought to be extremely old - over 12 billion years, over twice the age of the Earth - and presumably formed in an era of the universe when heavy elements are sparser than they are now. This strongly implies that something is wrong with Gonzalez's confident assertions about the probability of planet formation, and very probably indicates that the process is not as difficult or as unlikely as he implies.
As far as extremes of radiation - as with extremes of temperature and salinity, which were discussed in the previous part - once again the creationists have underestimated life's adaptability. There are already Earth species that can survive levels of radiation well in excess of what humans can tolerate. The reigning champion is Deinococcus radiodurans (see also), a bacterium which can survive a dose of 15,000 grays (10 grays is lethal to a human). D. radiodurans has been found living in the cooling water of nuclear reactors. The microscopic animals called tardigrades are nearly as resilient, able to withstand not just high doses of radiation but also high pressure, the vacuum of space, and temperatures well above boiling or just above absolute zero.
Of course, these are microscopic creatures, not large, complex life. But how do we know that the adaptations they possess couldn't have been transferred to creatures more like us? The Earth's environment has never been so extreme as to provide an evolutionary pressure in that direction, but there's no obvious reason to believe it's impossible. (Withstanding high doses of radiation is mainly a matter of DNA repair mechanisms.)
The creationists who parade these horribles before us want us to believe that life is fragile, just barely clinging to existence, and even a small perturbation to the environment would spell our doom. (One wonders why they're not more fervent about opposing global warming, if that's so.) But the evolutionary record reveals precisely the opposite: life is a tenacious phenomenon, able to survive in a wide variety of environments from the frozen arctic to the boiling-hot vents on the ocean floor, from arid deserts to salt-saturated ponds, and even in the vacuum of space. It's worth wondering whether, if creationists like Strobel were willing to acknowledge the true breadth and depth of life's history, they might be willing to give it more credit for being able to flourish in unlikely places.
Other posts in this series:
The Case for a Creator: A Parade of Horribles, Part I
The Case for a Creator, Chapter 7
Most of chapter 7 focuses on Guillermo Gonzalez's "privileged planet" hypothesis. This argument, as he uses it here, consists of listing every way in which our planet or our solar system could have been different, and concluding that every single one of them would be completely fatal to life.
Throughout this chapter, neither Strobel nor Gonzalez ask any of the obvious follow-up questions, such as whether different kinds of life could exist in these conditions, whether life like Earth's could have adapted, or even whether there are living things on Earth that already deal with very similar challenges (as we'll see, in many cases, there are). Instead, their reigning assumption is that life as a whole is as fragile as a soap bubble, and even a single change to Earth's parameters would have been catastrophic for the entire biosphere.
There are more arguments tossed out in this chapter than I could do justice to in a single post, so I'm splitting my responses up into several parts. This is the first post of what will either be two or three.
According to Gonzalez, the presence of Jupiter in our solar system "acts as a shield to protect us from too many comet impacts" [p.173]. Jupiter's enormous mass and gravitational pull "deflects comets and keeps many of them from coming into the inner solar system, where they could collide with Earth with life-extinguishing consequences... If you want to get an idea of the stuff that probably would have hit the Earth [without Jupiter], look at the surface of the moon." [p.174]
I'm not sure what point Gonzalez thinks he's making here. Is he saying that Jupiter's gravitational pull somehow shields the Earth but not the Moon? The two are so close, in astronomical terms, that any reputable scientist would find this laughable. Rather, the Moon's surface preserves evidence of the kind of bombardment that both the Earth and the Moon were subjected to early in the history of the solar system, Jupiter's presence notwithstanding. The Moon, which has no erosion, still bears these scars, while the Earth has largely erased them.
Although there's no denying that Jupiter's gravitational shield has deflected many cosmic objects that could otherwise have made it into the inner solar system, I'm far from convinced that this is an absolute necessity. As just mentioned, Earth did suffer a heavy bombardment early in its history, but that did not prevent life from forming here (soon after the bombardment had ended, in fact). Today, most of the lingering planetesimals and other stray rocks left over from the solar system's formation have been cleaned out, and large impacts on our planet are relatively infrequent, Jupiter or no. And even when Earth has been hit by large objects, although mass extinctions ensued, life as a whole did not die out.
Next on Gonzalez's list is the low eccentricity of the Earth's orbit - i.e., the shape of our orbit is nearly circular. This keeps us in what he calls the "circumstellar habitable zone", the Goldilocks region where liquid water can exist and the planet neither overheats, like Venus, nor freezes, like Mars.
"So if the Earth's distance from the sun were moved by, say, five percent either way, what would happen?" I asked.
"Disaster," came his quick reply. "Animal life would be impossible." [p.174]
What Gonzalez ignores here is that the Earth's climate is not wholly determined by the solar flux. The composition of our atmosphere - the concentration of heat-trapping greenhouse gases like water vapor, methane and carbon dioxide - determines how much of the Sun's warmth our planet retains. In fact, we depend on a moderate greenhouse effect to sustain life. "Circumstellar habitable zone" or no, the Earth's surface temperature would be below freezing if not for our atmosphere.
It's not hard to believe that a change in atmospheric composition could keep our planet livable even if we were closer to, or farther from, the Sun. In fact, the Sun's output of energy is not a constant, but has changed dramatically - not by a mere 5%, but by as much as 30% - over the lifetime of our solar system. Yet the Earth's geologic records show that it's had a warm surface and liquid water throughout that time. This is the so-called faint young sun paradox, and the favored scientific explanation does invoke changes in atmospheric greenhouse gas concentrations.
And even if the Earth's temperature did vary due to a more elliptical orbit, there's no reason to believe that would have been disastrous for life. Richards claims, "It doesn't do you any good to have melted water for four months and then have the whole planet freeze up again" [p.174]. I'm sure that would come as a surprise to the arctic species that already cope with very similar conditions: a brief, warm growing season followed by months of dark and cold. In fact, some geologists believe that around 700 million years ago, nearly the entire planet was covered with ice, and that did not extinguish life either.
ID advocates are particularly enamored of the Moon, especially since we've learned that it formed from a gigantic impact early in the solar system's history - the kind of unlikely event that they love to use as evidence of divine providence. Quoth Gonzalez:
"There was a remarkable finding that the moon actually stabilizes the tilt of the Earth's axis... The tilt is responsible for our seasons." [p.179]
He does not explain why the existence of seasons is a prerequisite for life; nor does he address the obvious point that equatorial and arctic regions, which experience little seasonal variation, support plenty of life.
Gonzalez goes on to say that if the Moon were not there, Earth's axial tilt could vary wildly, and if it were much more massive, it could slow down the Earth's rotation far more than it does. Either way, he worries, "you could have large temperature differences between day and night." [p.180]
Again, there are already species on Earth that cope with large temperature swings between day and night. The Sahara Desert, for example, sees diurnal variations of almost 100°F, but is not lifeless - the major limiting factor for life is the availability of water, not the temperature.
It's probably true that living on Earth would be more difficult if there were more frequent asteroid impacts, or more drastic temperature swings, or more chaotic seasonal variation. But this is a far cry from saying that life on Earth would be impossible. Based on the climactic extremes that other living species and even other human societies already deal with, we have every reason to believe that life would continue to thrive, even in the presence of the parade of horribles that Gonzalez invokes.
Other posts in this series:
The Age of Wonder
If you search the internet, it's not hard to find New Agers and others who think that the dawning of the age of reason was a mistake. They envision a more "holistic" approach, one that properly pays heed to the mystery and complexity of existence, and castigate science for being cold, unfeeling, heartless in its probing, reductionist scrutiny of the natural world. For example:
The reason things are advancing so slowly... is that science has neglected the (spiritual) indications necessary for its efficient performance - "with all your heart and all your soul...." -- indications that govern higher creativity and exist for the specific purpose of breaking the cosmic bank. The upshot is that science has become excessively expensive, bureaucratic and materialistic. The integration we need, external and internal, requires an incomparably more intense confrontation between the spirit of the researcher and the natural phenomena he is contemplating than what is currently practiced by even the most zealous of researchers.
And yet, the age of reason is also an age of wonder. The devotees of superstition and pseudoscience do not know what they are missing. In grasping after fool's gold, they have missed the true vein. The universe is a grander, more majestic and more beautiful place than any human being has ever imagined, or can imagine. The unsubstantiated and anthrocentric claims and inventions of people can never compare to the wonder and mystery held by reality as it truly is, and now that we truly have begun to understand how the cosmos works, we are at last getting a glimpse of that awe and wonder.
Consider what we witness when we peer into the cosmos with our telescopic eyes. We see light born billions of years ago in the crucible of dying stars, shining out across the cosmos and becoming ever more diffused, until at last our telescopes captured the lonely few photons that arrive bearing news of stupendous, ancient catastrophes. We see colliding galaxies, matter swirling into the abyss of black holes, and stars exploding with titanic force, sending out jets of energy visible across the known universe.
Our astronomy bears witness to births as well as deaths. We sift invisible light and see the ripples in the faint microwave glow that bathes all of space, distant echoes of the incomprehensible cauldron of heat and density in which the universe itself was born. We see dense nebulae where new stars are being born, burning away the dusty cradles of their formation like sunrise through fog. We see young planets circling their parent stars, their gravity cutting clear swaths through the veils of gas surrounding them. Most of the planets we have detected are hot Jupiters, but perhaps in some of these systems lurk embryonic Earths, awaiting their chance to cool and condense and one day become cradles of life of their own.
Turning closer to home, our emissaries have explored the solar system and brought back news of the other shores that await us. We have seen the shadows of the setting Sun creep across the mountains of the satellites of Jupiter, and we have seen the Earth rise in the night sky from the surface of the Moon. We have traveled the surface of Mars with our robot rovers, and sent landers parachuting down to the methane seas of Titan. Our age, for the first time ever in our planet's history, has sent ambassadors voyaging so far beyond our own shores that they could look back and see the Earth itself, our one and only home, as a pale blue point of light drifting in infinite dark.
Closer still, we have turned our gaze back upon ourselves, exploring our world in all its complexity. We have learned of the web of evolutionary kinship that connects all life on Earth. Everything - from human beings to redwood trees, from the lowliest cyanobacterium to the fluorescent tube worms on the ocean bottom - is a branch of the same family tree, every living creature a cousin, however distant, to every other.
We have delved down to the molecular roots of life itself, glimpsing the intricate choreography that turns inanimate molecules into living, growing cells, and the equally intricate assemblage that builds living cells into living beings. We have begun an effort to survey the tree of life, discerning the family relationships among countless species living and dead, and mapping the vast, frozen structure branching multidimensionally through those sections of design space that evolution has so far explored.
Traveling down into Earth's history, we have learned to read the record of the rocks and the chronicles they tell. We have retraced the multimillion-year drifting of the continents and learned of the planetary convulsions that wiped out whole branches of the tree of life and ushered in new ones in their place. We have glimpsed primordial eras long before humanity and envisioned the strange landscapes that once existed where we now place our feet.
All these findings far exceed the most fantastic imaginings of ancient mythology or modern pseudoscience, not least because they are true. In what other age of human history has anyone been able to look on a shooting star or a volcano and know what it really is? In what other age have we known the true age of the planet or understood the power source of the sun? These wonders and countless others, most of which are familiar and mundane to us, would have made people of past ages gasp in awe.
Out of the entire span of human history, these breathtaking discoveries have been made only in the last few hundred years, when we began to think and explore rationally. It was not crystals or prayer or Tarot cards that brought us these things. It was not superstition that was responsible, nor mysticism, nor credulous acceptance of extraordinary and unverified claims. It is the scientific method – institutionalized skepticism, rigorously and comprehensively applied – that has given rise to these wonders of understanding and accomplishment. As long as we human beings were willing to blindly accept the claims of others, to be meek and easily led, to believe without questioning, we remained frightened, brutish, short-lived and ignorant. There are some today who would gladly have us return to that state. Worse, there are some whose methods would inadvertently lead us back to that state, even as they hypocritically seek to take credit for the fruits and innovations of science while rejecting its rules.
But as for me, I remain a skeptic. I am proud to call myself a rationalist. And I will always fight against the proponents of darkness and unreason, because I believe that humanity has barely begun to tap its potential, and that if we continue the path of science, we may some day create wonders we currently lack the ability even to dream of.
TV Review: Planet Earth
I recently finished watching Planet Earth, the award-winning BBC nature documentary series narrated by David Attenborough. As its title implies, Planet Earth is an effort of considerable ambition: the filmmakers set out to produce a series that would provide a survey of our world's natural grandeur and biodiversity. To a remarkable extent, I think they succeeded. Of course the full richness of Earth's biosphere could not be exhaustively chronicled, but this series touches on many of the high points. It sweeps across every region of the planet, documenting our world's remaining wildernesses and some of the more important species that live in them, in the process filming things that have never been caught on camera before. In its scientific breadth and scope, in the beauty it depicts, and in the reasons it gives us both to fear, and more importantly, to hope, Planet Earth compares favorably to Carl Sagan's Cosmos.
The series consists of eleven episodes, each of which chronicles a different type of ecosystem flourishing on our planet. Over the course of the series, we're taken from icy tundra and boreal forest to tropical jungle, from the rich shallow seas to the blackness of the ocean abyss, from soaring mountains to desolate deserts to the eerie dark worlds of the cave systems beneath the planet's surface. Each episode is fifty minutes, plus a ten-minute ending segment called "Planet Earth Diaries" that shows how some of the more difficult-to-obtain shots were filmed - a nice touch that gives one appreciation for the truly heroic dedication of the photographers who traveled to some of the most remote, wild areas of the planet, braving all manner of harsh and grueling conditions, and worked in some cases for weeks on end just to catch a few moments of action on film. Three additional episodes, collectively titled Planet Earth: The Future, make the case for conservation using footage from the series and interviews with prominent advocates for the environment.
But the focus of the show, as I said, is on the breathtaking natural beauty of our planet and the wonderful, intricate tree of life that flourishes upon it. I couldn't do justice to all the high points in this one post, but here are a few that particularly stood out to me:
- a snow leopard, one of our planet's rarest and most elusive predators, hunting twisted-horned markhor antelope in the Himalayas of eastern Pakistan - the first close-up images of snow leopards in the wild ever filmed;
- the vast precipice of Venezuela's Angel Falls, the world's highest waterfall - a sheer drop of nearly a kilometer, so high that the falling water is blown into mist before it reaches the bottom;
- Nile crocodiles exploding out of the water to grab migrating wildebeest crossing their river - the terrifying tenacity of the bull crocodiles is shown when one of them, after grabbing a wildebeest's leg in its jaws, wrestles with its unlucky prey for over an hour before finally dragging the wildebeest into the water and drowning it;
- parachute divers leaping into the sunlit shaft of Mexico's Cave of Swallows, a dizzying sheer drop deeper than the Empire State Building is tall;
- a male polar bear, starving and exhausted after a long swim in the open water of the melting Arctic, desperately attacking a herd of bull walruses;
- a spectacular sequence in which an entire pride of African lions hunts and kills an elephant;
- the elaborate courtship displays of New Guinean birds of paradise;
- a band of chimpanzees waging war on a rival tribe, slipping silently into their adversaries' territory before erupting in a furious charge of intimidating shrieks and hoots; the savage hand-to-hand fighting ends with the losers being torn apart and, in some cases, devoured by the winners;
- banded sea kraits - aquatic snakes - swimming as smoothly as eels to hunt fish among the coral reefs of the Pacific;
- Borneo's Deer Cave, where a flock of three million bats has created a guano mound the size of a large building, covered with swarming, voracious cockroaches;
- in the Azores, a school of hundreds of dolphins herding scad mackerel, working in unison to encircle their prey and drive them closer to the surface, where diving cory shearwaters soar down to share in the hunt;
- the lush communities of strange life that thrive around hydrothermal vents on the ocean floor, powered by the superheated plumes of mineral-rich water erupting from fissures in the crust, like oases in the abyssal dark. When these vents stop erupting, a whole community can collapse from vibrant life into a dead, frozen forest of tube-worm skeletons - a devastation treated by the film with all the gravity of an empire's fall;
- a vast flock of migrating Baikal teal - hundreds of thousands of birds, all flying in unison - and the camera pulls back, and back, and still further back, until each individual bird is just a tiny speck, and still the whole flock cannot fit on the screen at once;
- and last but not least, time-lapse shots of the seasons changing, even time-lapse shots from space that show rivers flood, forests turn green, snow and glaciers advance - I don't know how these were taken or whether they were special effects.
The one caveat I would offer is that Planet Earth is a nature documentary, which means most of the sequences are of animals doing what animals normally do in the wild. If you're the kind of person who finds that boring, you'll probably be bored by this as well. There are plenty of hair-raising moments, but the purpose of the show is not to keep viewers constantly on the edge of their seat. Personally, I found it a spectacular glimpse of some of the Earth's last remaining places of wild beauty. If that description appeals to you, then I can safely say that you'll love Planet Earth, and I would definitely recommend it.
February 2008 Science Updates
There's been so much important news pouring in this month that it's hard to keep up with it. But despite the flood of information, there've been a few especially significant discoveries that I think shouldn't be overlooked. There are three that I thought deserve special notice:
• On February 13, astronomers announced the discovery of a new solar system that resembles our own more closely than any exoplanetary system that was previously known. The new system, given the unlovely designation of OGLE-2006-BLG-109, is about 5,000 light-years from Earth in the direction of the constellation Scorpius. The home star of this system is about half the mass of the Sun, and thus cooler. It's orbited by at least two planets, both gas giants, one 0.71 times the mass of Jupiter orbiting at a distance of 2.3 astronomical units (1 AU = 93 million miles), and one that's 0.27 times Jupiter's mass and orbiting at a distance of 4.6 AU - both of which now join the nearly 230 exoplanets previously known.
This marvelously specific discovery was made using a new method, called gravitational microlensing. Many exoplanets have been detected by looking for the Doppler shift in a star's light as an orbiting planet tugs it back and forth. But this method is most sensitive to large Jupiter-like planets in close-in orbits, not the best analogues of our own solar system. The new method relies on a chance alignment of stars from our vantage point, in which the light of the background star is bent and magnified in a telltale way by the gravity of the foreground star. Although not yet sensitive enough to detect terrestrial planets like our Earth, the possibility of such planets in this system hasn't been ruled out. Since this star is cooler than our Sun, there could be a habitable zone further in than the orbits of the two giant planets.
What I loved best about this discovery is that it was assisted by two amateur New Zealand astronomers, Jennie McCormick and Grant Christie, using 10-inch telescopes in backyard observatories. Even in this age of multibillion-dollar particle accelerators and space telescopes, I find it greatly inspiring that even a non-professional can still contribute to groundbreaking scientific discoveries.
• On to biology: The peerless Carl Zimmer tells us about a new transitional species in the increasingly complete fossil series that documents the evolution of whales. The 25-million-year-old Aetiocetus provides a key piece in what was a vexing puzzle: how did baleen whales evolve from toothed ancestors?
In the paper, the authors report that Aetiocetus had both teeth and baleen, based on the fossil evidence. Its skull had teeth as well as special bone troughs called nutrient foramina, which supply baleen tissue with blood in modern baleen whales and are not present in modern toothed whales.
• And another transitional fossil - this one a step in the evolution of bats. Named Onychonycteris finneyi, it comes from 52-million-year-old rocks of the Green River formation in Wyoming and is nested more deeply in the bat family tree than any bat species previously known. Although it was capable of flight, it also had several primitive characteristics not found in any living bat, including five well-formed claws on each wing, and an unusual, half-gliding/half-fluttering flying style seen in few modern bats. Based on its inner ear, it also lacked the ability to echolocate. Carl Zimmer, again, writes that it reminds him of Archaeopteryx, another electrifying specimen that gave us a glimpse into the progress of evolution over deep time.
When we were young, we looked up at the twinkling lights in the night sky and wondered. Most of them were immovable, fixed stars rising and setting in the same place every night as if pinned to the dome of the firmament. However, a very few of those lights were not so steady. Instead, they seemed to meander, moving perceptibly across the sky from night to night - sometimes even changing course and moving backwards for a time, as if in a spirit of play. We named these vagabond stars planets, after the Greek word planetes, which literally means "wanderer".
For many long centuries, the nature of these wanderers was unknown to us. Our wise theologians advised us that they were no more than lights affixed to nested crystal spheres that rotated around us, placed as signs and portents so that we could marvel at the power of the cosmic Designer who framed them. Even the moon, closest to our own earth, was an orb of mystery whose ever-changing faces became synonymous with the unsettling and the strange.
But then we discovered how to grind glass to focus light, and distant rays streaming into our retinas brought illumination: the planets are not mere lights after all. They are places, whole worlds of their own, both like and unlike the Earth. They have mountains and valleys, craters and river channels, deserts and ice caps, and spectacular night skies of their own with rings, satellites, and one other wandering, blue star. It is true, our species has walked on the moon; we have taken our first tentative steps into that vast cosmic ocean that surrounds us. But there are other vistas that await us. Far from our humble yet beautiful world, there are other shores upon which no human being has ever set foot.
Yet where we have not traveled, our emissaries have gone before us: bright-eyed creatures with limbs of silver and gold, seeing into subtle bands of the spectrum we can only imagine. They hurtle unscathed through the vacuum of space, tireless through the long journey, until at last they reach their destination: an oasis appearing out of the void, a distant twinkle of light that swells into a vast new world. In obedience to the faint voices from their place of origin, our heralds swing into orbit around these distant shores, or descend to their surfaces. And there they have found magnificent beauty - landscapes of gorgeous desolation, of primordial power, of grand intricacy; landscapes that tell stories of an ancient history, a history that passed countless eons unregarded and unknown - until now. And what our messengers see, they report back to their makers.
At right is a magnificent image of Saturn, from high above the ringed planet's north pole, taken on January 19 by the Cassini spacecraft now in orbit around that world. This is a natural-color view: if a human being was in this orbit, they would see the same image that Cassini saw. So fantastically perfect as to be almost unreal, Saturn sits half in sunlight and half in darkness, casting a vast shadow across the plane of its majestic rings. Stark and geometric in its clarity, the image makes it almost too easy to forget that this is not a mere model, but a vast world of its own, a gas giant larger than hundreds of Earths. Only Cassini's celestial perspective, like a god looking down from on high - this picture was taken from a distance of three-quarters of a million miles - renders Saturn's alien beauty as comprehensible as it is.
The Cassini mission has glimpsed other wonders as well. It took seven years of travel through the void for the probe to reach Saturn - a stark reminder of how enormous the distances are that separate us from even the nearest fellow worlds - but there were chances to survey other shores along the way.
At left is a true-color mosaic of the planet Jupiter, taken in December 2000. The gas giant is a world of clouds, banded with swirls of weather in intricate patterns of turbulence, wreathing and diffusing like smoke in air or colorful ink in a glass of milk. In the southern hemisphere, the vast cyclonic storm system called the Great Red Spot continues to roil and churn the atmosphere, as it has been doing since it was first observed by the astronomer Giovanni Cassini, in whose honor the current mission is named, in the 1600s.
When it comes to the truly cosmic, it is all but impossible for a limited human being to grasp the sense of scale. However, it may help to see how large the Earth is in comparison. In comparison to regal Jupiter, all the distant lands and mighty seas where Earth's most famous explorers dared to venture are but a ripple in an unimaginably more enormous ocean of atmosphere. Though Jupiter has no solid surface on which to tread, a traveler who could soar through its upper reaches could spend a thousand human lifetimes and never see more than a tiny fraction of the stunning vistas that must surely await there.
Above: An image of Titan from Cassini. Dense clouds hide the planet's surface.
But Jupiter and Saturn, for all their grandeur and their beauty, were not the Cassini probe's only destinations. The ringed planet has a moon, named Titan - a world of unfathomable mystery, one that may even hold the keys to understanding the origin of life on our own blue planet.
Titan is the only moon in the solar system with a substantial atmosphere, one that is actually denser than Earth's. But a dense orange haze clouds Titan's atmosphere and hides its surface from view, and until recently we had no idea what lay beneath the clouds. There have been tantalizing hints. Based on spectroscopic observations and laboratory experiments similar to the famous Miller-Urey experiment, the late Carl Sagan concluded that Titan's haze might be made of a muddy mixture of organic compounds called tholins - possible building blocks of life - that were constantly raining down on the moon's surface like manna falling from heaven.
It has long been conjectured that lakes of liquid methane and ethane might exist on Titan's frigid surface, and that these hydrocarbon lakes could be the source of the Titanian tholins. Evaporating and rising into the atmosphere, these simple compounds would be broken down by ultraviolet radiation from the Sun, recombining into the more complex organic molecules that shroud the surface in haze. But this idea is mere speculation no longer. Cassini's radar can pierce the clouds of Titan, and several weeks ago, it returned this false-color image of dark, smooth patches of liquid on the moon's rough surface - the long-hypothesized hydrocarbon lakes, glimpsed at last.
But we have done more than just examine Titan from orbit. The Cassini spacecraft carried a lander, Huygens, which parachuted down to the moon's surface to report back on what it found. Here is one of the images it returned, a true example of an almost unimaginably distant shore:
Above: An image of Mars taken by Viking 1. In the foreground, the vast Valles Marineris canyon system slices across the surface of the planet.
Not every shore we visit is as exotic as ringed Saturn or cloud-shrouded Titan. Our planetary neighbor Mars, compared to these strange and distant worlds, is practically a close friend, and we know it with familiarity befitting that designation. Both on the surface and from orbit, our robotic servants have mapped and explored Mars, peeling back the eons of its history, and uncovering stunning evidence of its past. Too small for its gravity to hold an atmosphere as dense as our own, Mars is now a dry, freezing desert, with an ethereally thin atmosphere and regular planet-wide dust storms. But we now know that it once had a warm, clement past complete with liquid running water, the prerequisite for all life as we know it. Astonishingly, Mars' polar ice caps contain enough water to flood the entire planet to a depth of over thirty feet, and its surface bears signs of past reworking by water on a colossal scale. And though we have not yet found evidence of life on Mars, neither have we ruled out the possibility that it may still exist beneath the planet's rusty soil.
Below is an image of the striking Martian surface feature known as Victoria Crater, the half-mile-wide scar of some ancient impact, taken from space by the Mars Reconnaissance Orbiter:
And here is an image of Victoria Crater's rim from the surface, courtesy of the robotic rover Opportunity that is now exploring it:
Opportunity's twin, Spirit, has not been slumbering either. Here is Spirit's current view, the McMurdo Panorama, a landscape of desolation that nevertheless seems strikingly Earthlike:
Despite its loneliness, Mars can present scenes of astonishing beauty. On occasion, Spirit has even had the chance to pause from its scientific work and simply admire a sunset, so familiar and yet so strange, such as this one taken at Gusev Crater from April 2005:
Images like this are a much-needed reminder that the Earth is not the only place in the cosmos. Though the Earth is all we know, and sometimes this leads us to myopically imagine it is all there is, there is a whole universe of landscapes awaiting us. Our solar system alone contains a multitude of gorgeous and fantastic scenes which no human was ever privileged to see - until now.
In a very real sense, everyone alive today is an explorer on a scale more profound than the seafarers of bygone ages ever conceived of. Not with our bodies, but with our eyes and minds we have traveled forth to begin exploration of the cosmos. Images like this should teach us a valuable lesson in humility, a reminder that we are not the center of the universe. Yet at the same time, they should rightfully fill us with awe and wonder. There are wholly new worlds awaiting our study, places stranger and yet more beautiful than we could have imagined. How can such a revelation not fill us with joy?
(All images in this post courtesy of NASA/JPL-Caltech.)