Sciency Words A to Z: Wow! Signal

Welcome to a special A to Z Challenge edition of Sciency Words!  Sciency Words is an ongoing series here on Planet Pailly about the definitions and etymologies of science or science-related terms.  In today’s post, W is for:


There’s a ton of radio noise in space, coming from stars and nebulae and black holes and so forth.  There’s so much radio noise that it can easily drown out the relatively weak radio and television broadcasts that might be coming from a planet like Earth.

So if aliens want to talk to us, they’re going to have to send a much stronger transmission, something that will come through loud and clear over all that other space noise.  And in 1977, astronomers at Ohio State University picked up exactly that kind of signal.

As the story goes, Ohio State was conducting a SETI search with their “Big Ear” radio telescope.  The telescope recorded electromagnetic emissions coming from space, reporting the strength of those emissions on a scale from 0 to 9. If Big Ear happened to pick up anything stronger than a 9, it represented that with a letter—A represented a 10, B represented 11, and so forth.

On the morning of August 18, 1977, astronomer Jerry Ehman was reviewing Big Ear’s latest data when he saw a bunch of large numbers, and even a few letters.  Famously, Ehman circled those letters and numbers and wrote one word next to them: Wow!

Image courtesy of Wikipedia

Appropriately, this is now known as “the Wow! Signal” (the exclamation point is usually included in the name).

In one sense, the Wow! Signal is exactly what SETI scientists were hoping to find.  Even the radio frequency—approximately 1420 megahertz—was consistent with expectations.  In this 1959 paper, physicists Giuseppi Cocconi and Philip Morrison singled out 1420 MHz as the frequency extraterrestrials were most likely to use.

But in another sense, the Wow! Signal was not what we wanted it to be, because it only happened one time, and it has never repeated since. Despite many follow-up searches of the constellation Sagittarius (like this one or this one), where the Wow! Signal originated from, we’ve never picked up a signal like it again.

As I’ve said several times this month, in our search for alien life, we have to hold ourselves to the same standards as a court of law: proof beyond a reasonable doubt.  The Wow! Signal very well might have been aliens… it might have been anything… and that’s the problem.  Unless and until we pick up the Wow! Signal again, we can’t prove one way of another what it was.

Next time on Sciency Words A to Z, you can’t have life without water.  Or can you?

Sciency Words A to Z: Viking

Welcome to a special A to Z Challenge edition of Sciency Words!  Sciency Words is an ongoing series here on Planet Pailly about the definitions and etymologies of science or science-related terms.  In today’s post, V is for:


You know, I’ve noticed something about those early pioneers in the field of astrobiology.  They thought they knew an lot about what aliens would be like, how aliens would behave.  It seems awfully presumptuous in hindsight.  People even thought they knew how alien microorganisms would behave.

In the late 1960’s, NASA was putting together a mission to Mars, and they decided to name this new mission Viking.

As explained in this book on NASA’s history of naming things:

The name had been suggested by Walter Jacobowski in the Planetary Programs Office at NASA Headquarters and discussed at a management review held at Langley Research Center in November 1968.  It was the consensus at the meeting that “Viking” was a suitable name in that it reflected the spirit of nautical exploration in the same manner as “Mariner” […].

In NASA’s early years, nautical exploration was the theme for naming all missions to other planets.

The Viking 1 and Viking 2 landers arrived on Mars in 1976. They were the first space probes to successfully land (as opposed to crash) on Mars, and they were the first to send back photos from the surface.  They were also the first, and so far the only, space probes to conduct experiments directly testing for Martian life.

And one of those tests came back positive!!!

Except it may have been a false positive.  It was probably a false positive.

This test was called the labeled release experiment, and here’s how it worked: the Viking landers scooped up some Martian soil and added a nutrient mix—in other words, we tried to feed the Martians.  The nutrient mix was “labeled” with a radioactive carbon isotope, so if any Martian microbes were living in the soil, they’d take the food and then release gaseous waste that had this special isotope in it.

But there were some problems with this idea.  How do we know what Martian microbes eat?  How do we know what waste products they produce?  And—here’s the biggest problem of all—given how little we knew about Mars at the time, how do we know our nutrient mix wouldn’t react with some previously unknown chemical in the Martian soil, giving us a false positive result?

These are the kinds of questions that were asked after the labeled release experiment took place (but apparently not before).  As a result, there was wild disagreement about what that positive test result might actually mean.  The general consensus today is that we got a false positive.  Our nutrient mixture must have reacted with something in the soil, something that was not alive.

But while the Viking Mission could not give us a definitive answer about whether or not there is life on Mars, Viking still taught astrobiologists a valuable lesson.  When exploring strange, new worlds, trying to tell the difference between chemistry and biochemistry can be really hard.

Next time on Sciency Words A to Z, wow… just, wow!

Sciency Words A to Z: Unknown Absorber

Welcome to a special A to Z Challenge edition of Sciency Words!  Sciency Words is an ongoing series here on Planet Pailly about the definitions and etymologies of science or science-related terms.  In today’s post, U is for:


If there’s one thing worth remembering from all this astrobiology stuff, it’s that life begins with chemistry.  All life in the universe, no matter how strange and exotic it may seem to us Earthlings, must depend on chemistry.  And I don’t know many places that are more chemically active than the planet Venus.  So is Venus a good place to go looking for alien life.

To quote from David Grinspoon’s book Venus Revealed, “Where life is concerned, Venus is consistently voted ‘least likely to succeed.’”  Sure, Venus is chemically active, but in a way that will violently tear apart complex organic molecules.

However, Grinspoon has the temerity to go ahead and speculate—and he makes it abundantly clear this is pure speculation—about the kinds of organisms that might call Venus home.  And that speculation focuses on a mysterious substance found in the Venusian clouds, a substance that has long been called the unknown near-U.V. absorber, or simply the unknown absorber.

In the field of spectroscopy, every chemical is known to absorb very specific wavelengths of light.  When light is spread out into a spectrum, as with a prism, you get a sort of unique barcode that you can use to identify chemicals.

A very simple “barcode” representing hydrogen.

If you’ve ever wondered how astronomers know which chemicals are found in space, or on other planets, this is how they do it.

In 1974, NASA’s Mariner 10 spacecraft sent us our first ever close-up photos of Venus.  In the visible part of the spectrum, there were no real surprises, but photos taken in ultraviolet showed that something was absorbing U.V. light like crazy, producing a spectroscopic barcode that nobody recognized.

In his speculation about life on Venus, Grinspoon mentions another chemical with a complex, hard-to-identify spectral barcode: chlorophyll, the chemical that makes photosynthesis possible here on Earth.  I say hard-to-identify… it’s not hard for us to identify, because we already know what it is.  But if extraterrestrial observers were studying Earth’s spectrum, chlorophyll would have them very confused—almost as confused as we were by Venus’s unknown absorber.

So could the unknown absorber be a chlorophyll-like molecule? Could this be the first evidence of air-born bacteria, drifting around in Venus’s cloudbanks, performing their own version of photosynthesis?  Maybe, Grinspoon tells us in Venus Revealed.  But that book came out in 1997.  In 2016, this paper was published identifying Venus’s unknown absorber as disulfur dioxide.

On a personal note, I wrote a blog post about Venus’s formerly unknown absorber before, and my post got the attention of the lead author of that 2016 paper.

But even though the mystery of Venus’s unknown absorber may have been laid to rest, I think this still served as a valuable lesson about what we should be looking for out there in the cosmos. Someday, another unknown absorber, with another weird spectral barcode, may be the thing that leads us straight to the discovery of alien life.

Next time on Sciency Words A to Z, the Martians better watch out.  The Vikings have landed on their planet!

Sciency Words A to Z: Tholin

Welcome to a special A to Z Challenge edition of Sciency Words!  Sciency Words is an ongoing series here on Planet Pailly about the definitions and etymologies of science or science-related terms.  In today’s post, T is for:


Have you ever been stuck trying to say something, but you just don’t have the right words to say it?  In the 1970’s, planetary scientists Carl Sagan and Bishun Khare had that problem.

They’d conducted a series of experiments using gaseous chemicals that were known to be common in outer space, chemcials like ammonia, methane, water, hydrogen sulfide… they mixed all these chemicals together and zapped them with either an electric spark or ultraviolet light.  Then they studied the orangey-brown gunk that formed as a result.

Initially, this gooey gunk was thought to be a polymer, but as reported in this 1979 paper, Sagan and Khare soon determined that wasn’t what it was.

It is clearly not a polymer—a repetition of the same monomeric unit—and some other term is needed.

Sagan and Khare propose the word “tholin,” which is sort of a pun.  It’s taken from two Greek words that are spelled the same, except for an accent mark that’s shifted from one vowel to another.  One word means “muddy,” the other means “dome” or “vault,” as in the great dome or vault of the sky.  Sagan and Khare go on to mention that they were “tempted by the phrase ‘star-tar.’”

Tholin may be present on some asteroids and comets, and tholin or tholin-like material has been observed on several moons in the outer Solar System, most notably Titan.  We may have even found tholin on Pluto, and several other red-hued dwarf planets could have it too.

So what specifically is this stuff?  Well, I can’t really say.  Tholin is not a specific substance but rather a general category of organic matter.  As planetary scientist Sarah Hörst explains in this article:

The best analogy I have been able to come up with is “salad.”  Salad, like tholin, is a mixture of a number of different compounds and spans a fairly broad range of materials.  Most of us would agree on a case by case basis whether or not something is a salad, but the definition is not at all specific and the material itself depends on the starting materials, temperature, etc.

So there are many different tholins out there.  The tholin we might find inside a comet is probably different from the tholin we find on Pluto, which is different from the tholin we find on Titan.  What all these tholins have in common is that they’re the kind of yucky gunk you’d expect life to make, except life didn’t make it.

However, while life doesn’t make tholin, tholin could, in theory, be used to make life.  Or at least, once life gets started, tholin can serve as a source of food for primitive microorganisms.

Titan has long been the poster child for tholin chemistry, simply because Titan has so much of this stuff.  More than enough, you’d think, for some sort of biological activity to get started—assuming it hasn’t already!  However, with all that tholin lying around, sending astronauts to explore Titan properly may prove to be a sticky proposition.

Next time on Sciency Words A to Z, there’s no way we’ll find life on Venus… right?

Sciency Words A to Z: SETI

Welcome to a special A to Z Challenge edition of Sciency Words!  Sciency Words is an ongoing series here on Planet Pailly about the definitions and etymologies of science or science-related terms.  In today’s post, S is for:


In September of 1959, Italian physicist Giuseppi Cocconi and American physicist Philip Morrison published this paper, titled “Searching for Interstellar Communications.”  That paper is essentially the founding document for SETI, the search for extraterrestrial intelligence, which is now considered a subfield of astrobiology.

The SETI Institute, on the other hand, was established in 1984 by Thomas Pierson and Jill Tarter.  As stated in this report on the proper use of SETI nomenclature:

SETI should not be used as a shorthand for the SETI Institute, which is an independent entity and should be referred to by its full name to avoid confusion.

And let me tell you, this SETI vs. SETI Institute distinction… that really can cause a lot of confusion.

A few years back, I saw a report on the news.  SETI (the Institute, I presumed) had picked up a signal form outer space, from a star located 94 light years away.  According to the news lady on TV, a SETI spokesperson had this to say, and that to say, and some more stuff to say about this amazing discovery.  “Oh cool,” I thought, and I quickly went to the SETI Institute’s webpage to learn more.

There was nothing—absolutely nothing—about it.

Another day or two went by, and then this article was posted on the SETI Institute’s website.  Some Russian radio astronomers had picked up what they thought was a SETI signal (it eventually turned out to be a satellite).  Somehow the media picked up on this story and ran with it, apparently without contacting the SETI Institute—or speaking with any actual SETI Institute spokesperson—to find out if any of this were true.

I should probably mention that in my day job, I work in the T.V. news business.  This sort of sloppy journalism infuriates me, but I’ve found that it’s quite typical of how the popular press handles science news.

However, to be fair, prior to that misleading news report, I didn’t know to make a clear distinction between SETI and the SETI Institute myself. But I’ve tried to be more careful about this ever since.  Language can be a messy way to communicate, so it’s important to try to be clear about what we mean.  Otherwise, someone (perhaps even someone from the media) will get the wrong idea and run with it.

Next time on Sciency Words A to Z, the first astronauts on Titan may find themselves in a very sticky situation.

Sciency Words A to Z: Rare Earth Hypothesis

Welcome to a special A to Z Challenge edition of Sciency Words!  Sciency Words is an ongoing series here on Planet Pailly about the definitions and etymologies of science or science-related terms.  In today’s post, R is for:


Once upon a time, it was believed that the Sun, Moon, planets, and all the stars revolved around the Earth.  This was known as the geocentric theory.

Copernicus, Galileo, Kepler, and others set us straight about our planet’s physical location in space.  However, it is still sometimes asserted that Earth is special or unique in other ways.  Such assertions are often referred to in a derogatory sense as “geocentrisms.”

It’s tempting to dismiss the Rare Earth Hypothesis as just another geocentrism.  The idea was first presented in 2000 in a book called Rare Earth: Why Complex Life is Uncommon in the Universe by Peter Ward and Donald Brownlee.  In that book, Ward and Brownlee go through all the conditions they say were necessary for complex life to develop on this planet.  Crucially, they point out all the ways things could have gone wrong, all the ways complex life on Earth could have been prematurely snuffed out.

In other words, we are very, very, very lucky to be here, according to Ward and Brownlee, and the odds of finding another planet that was as lucky as Earth must be astronomically low.  Sure, there might be lots of planets where biology got started. Simple microorganisms may be quite common.  But complex, multicellular life like we have here on Earth—that’s rare.  And intelligent life forms like us are rarer still.  Perhaps intelligent life is so rare that we’re the only ones.

My favorite response to the Rare Earth Hypothesis comes from NASA astronomer Chris McKay.  In All These Worlds Are Yours, McKay’s argument is described as the Rare Titan Hypothsis.

Imagine intelligent life has developed on Titan (such a thing seems unlikely, I know, but there may be something living on Titan).  Titanian scientists look through their telescopes and soon realize that no other world in the Solar System is quite like their own.  Earth, for example, if too hot for life as the Titanians know it, and there’s far too much of that poisonous oxygen in the atmosphere anyway.  Furthermore, water would wreak havoc on what the Titanians would consider a biomolecule.

Perhaps a pair of Titanian scientists then decide to publish a book.  They list all the conditions required for complex life to develop on Titan, point out all the ways Titanian life could have been snuffed out prematurely, and argue that the odds of finding another Titan-like world must be astronomically low.

Personally, I think there’s some validity to the Rare Earth Hypothesis, but McKay’s point is worth bearing in mind.  There could be many different ways for life to develop in our universe.  Earth is but one example.  Planets that are just like Earth may indeed be rare—extremely rare—but there’s no reason to conclude that Earth-like life is the only kind of complex life out there.

Next time on Sciency Words A to Z… oh my gosh, we’ve finally made it to S!  It’s finally time to talk about SETI!

Sciency Words A to Z: Quijote

Welcome to a special A to Z Challenge edition of Sciency Words!  Sciency Words is an ongoing series here on Planet Pailly about the definitions and etymologies of science or science-related terms.  In today’s post, Q is for:


The International Astronomy Union (I.A.U.) still seems to think they were right about the whole Pluto thing.  However, they also seem to realize that they made a mistake in being so very dismissive of public opinion on the matter, and they’ve been trying to do a better job with public outreach since then.

To that end, in 2014 the I.A.U. announced a partnership with Zooniverse, and they enlisted the general public in the process of assigning official names to exoplanets.  As stated in this I.A.U. press release:

For the first time, in response to the public’s increased interest in being part of discoveries in astronomy, the International Astronomy Union (IAU) is organizing a worldwide contest to give popular names to selected exoplanets along with their host stars.

Now the I.A.U. already had a system in place for naming exoplanets, but that system produced “names” like HD 219134g, or KOI-4427b, or PSR 1257+12c.  There are astronomers who can rattle off this alphanumeric gobbledygook with ease, but I have a tough time with it.  As Doctor Who once said about planets: “I’m terribly old-fashioned. I prefer names.”

But of course letting the general public decide these sorts of things doesn’t always go well.  The I.A.U. did not want something like the Boaty McBoatface scenario to happen to some poor planet.

So the official process was that astronomy clubs and non-profit astronomy organizations (i.e.: people who would take this seriously) got to submit names, and then an I.A.U. committee picked the best options and put those up for a vote.

Quijote—as in Don Quijote (or Don Quixote, as it’s spelled in English) of the famous Spanish novel—was one of the winners.  According to Wikipedia, Quijote was initially thought to have a highly eccentric orbit, but after we learned more about the planet, it turned out its orbit was not as eccentric as it first seemed.  I’m not super familiar with the Don Quijote story, but from what I’ve heard the name seems fitting.

In that same I.A.U. naming contest, Quijote’s star got the name Cervantes, in honor of the author of Don Quijote, and all the other known planets in the system were named after other characters from the book.  As for astrobiological interest in Quijote, the planet does lie within Cervantes’ Goldilocks zone; however, Quijote is a gas giant, so it’s E.S.I. score must be quite low.

Still, it’s conceivable that Quijote might have Earth-like moons. So as we continue our quixotic search for alien life, Quijote might not be a bad place to check.

Next time on Sciency Words A to Z, could it be that we really are alone in the universe?

P.S.: Scattered disk object (225088) 2007 OR10 is currently the largest unnamed object in the Solar System.  If you’d like to vote on what the I.A.U. should name it, click here.

P.P.S.: I cast my vote for “Holle,” the only female name on the ballot, because I think we need more female representation in the cosmos.

Sciency Words A to Z: Panspermia

Welcome to a special A to Z Challenge edition of Sciency Words!  Sciency Words is an ongoing series here on Planet Pailly about the definitions and etymologies of science or science-related terms.  In today’s post, P is for:


Pictured above is a tardigrade, also known as a water bear.  Tardigrades are pudgy-looking, almost cuddly-looking (depending on the photograph) microorganisms that reside here on Earth.  But due to some alleged confusion about their genetic lineage, it was at one time speculated that tardigrades might have come from somewhere else.  Perhaps they migrated to Earth through a process called panspermia.

The word panspermia goes all the way back to ancient Greece, and it can be translated to mean “seeds everywhere,” as in the seeds of life have spread all over the universe.  According to this article by Chandra Wickramasinghe, one of the leading proponents of the panspermia hypothesis, serious scientific discussion of the idea began in the late 1800’s.  In Wickramasinghe’s article, Lord Kelvin is quoted thusly:

… Hence, and because we all confidently believe that there are at present, and have been from time immemorial, many worlds of life besides our own, we must regard it as probable in the highest degree that there are countless seed-bearing meteoritic stones moving through space.  If at the present instant no life existed upon the Earth, one such stone falling upon it might, by what we blindly call natural causes, lead to its becoming covered with vegetation.

While Lord Kelvin and other late 19th and early 20th Century scientists may have taken panspermia seriously, the idea soon fell out of vogue.  Yes, from time to time, perhaps a “meteoritic” impact or a volcanic explosion (or maybe even a really strong gust of wind) might loft a few bacterial spores into a planet’s upper atmosphere.  Perhaps those spores could then escape into space.  But surely those spores would not survive for long after that.

It was British astronomer Fred Hoyle and Sri Lankan-born British astronomer Chandra Wickramasinghe who repopularized panspermia in the 1970’s and 80’s.  As explained in this paper, titled “Progress Towards the Vindication of Panspermia,” the Hoyle-Wickramasinghe interpretation of panspermia is founded on two basic premises: that microorganisms “have an almost indefinite persistence and viability,” and that once they find themselves in the right environment, “microbes can replicate exponentially.”

I’d say both of those premises make sense.  We all know how rapidly microbes can replicate given the chance.  As for their “almost indefinite persistence and vitality”… tardigrades famously survived in the vacuum of space.  No air, no water, extreme temperatures, extreme radiation… the tardigrades handled space quite well. Other microorganisms also survived similar experiments.

But could these microbes survive the thousands or perhaps millions of years it would take to travel from one planet to another?  Hoyle and Wickramasinghe clearly thought so, and they made some pretty outrageous claims about how much biological material we should expect to find drifting through open space.

[…] by 1983 we inferred confidently that some 30 percent of the carbon in interstellar dust clouds had to be tied up in the form of organic dust that matched the properties of degraded or desiccated bacteria.

Panspermia is now one of the most important concepts in the field of astrobiology.  It’s gained a lot of credence, especially since the discovery of those bacteria shaped objects in the ALH84001 meteorite.  However, although it is an important concept, it also remains highly speculative.  As I’ve said several times now in these A to Z posts, astrobiologists must hold themselves to the same standards as a court of law: proof beyond a reasonable doubt.  And there are still plenty of reasonable doubts about panspermia.

Next time on Sciency Words A to Z, call me old fashioned, but I prefer it when planets have names.

Sciency Words A to Z: Oxygen Catastrophe

Welcome to a special A to Z Challenge edition of Sciency Words!  Sciency Words is an ongoing series here on Planet Pailly about the definitions and etymologies of science or science-related terms.  In today’s post, O is for:


Oxygen.  What could be more healthy or more wholesome to life than oxygen?  But oxygen is, in fact, one of the most dangerous and deadly chemicals on Earth.  It is, as you might easily guess, a powerful oxidizer, and it reacts with just about everything—especially organic matter!

True, life on Earth as we currently know it would not be possible without oxygen, but left to its own devices oxygen would eagerly burn us all up.

It started with cyanobacteria (also known as blue-green algae).  Cyanobacteria were the first organisms on this planet to develop photosynthesis, a process that uses sunlight to convert water and carbon dioxide into biomolecules.  But photosynthesis also produces hazardous oxygen as a waste product.

Things were okay for Earth’s biosphere for a while, but eventually the oxygen situation turned deadly.  As David Grinspoon explains in his book Earth in Human Hands:

For hundreds of millions of years, the cyanobacteria kept spitting out oxygen, but all the excess was hungrily snapped up by the abundant iron in Earth’s crust and interior.  Yet eventually, around 2.4 billion years ago, the crust was thoroughly oxidized and there was no more available iron lying around.

Grinspoon goes on to explain how life would eventually learn to protect itself from the harmful effects of oxygen exposure and even learn to control oxygen, transforming what was (and still is, in some respects) a deadly poison into a valuable and powerful new fuel.

Before we evolved that ability, however, the buildup of corrosive oxygen in the atmosphere was massively fatal for most of the species that existed on Earth at the time.

This event, approximately 2.4 billion years ago, is generally known as the Great Oxidation Event, but it’s also sometimes called the Oxygen Catastrophe.  I prefer calling it the Oxygen Catastrophe, because the consequences were truly catastrophic for almost everyone who was not a cyanobacteria. This was, in fact, Earth’s first mass extinction event.

As we continue our search for alien life, I think it’s important to keep oxygen’s true nature in mind.  To us, oxygen means life, but it could just as easily be seen as a deadly poison.  There may be other worlds out there was “poisonous” atmospheres, and those worlds may turn out to be the ones we should pay the most attention to.

Next time on Sciency Words A to Z, what if life on Earth started somewhere else?

Sciency Words A to Z: Noachian

Welcome to a special A to Z Challenge edition of Sciency Words!  Sciency Words is an ongoing series here on Planet Pailly about the definitions and etymologies of science or science-related terms.  In today’s post, N is for:


In the 1870’s, Italian astronomer Giovanni Schiaparelli began producing the most detailed and accurate maps of Mars anyone had ever seen.  Schiaparelli also assigned many of the names we still use today for Martian surface features today. One of those regions on Schiaparelli’s map got the name Noachis Terra—the Land of Noah.

In my opinion, no other name could have turned out to be more apt.  Schiaparelli got many of his names from the Bible, and I’m sure you remember the biblical story of Noah and the Great Flood.

Schiaparelli’s map of Mars.

Much like the geological history of Earth, Mars’s geological history is divided up into different periods.  Noachis Terra spawned the name for Mars’s Noachian Period, a time that roughly corresponds with the Archean Eon here on Earth—the time when the very first microbes were appearing on our planet.

So what was happening on Noachian Mars?  Based on the evidence presented in this textbook on Astrobiology, it wasn’t quite like the Great Flood in the Bible, but it was close!  Most if not all of Mars’s northern hemisphere was probably covered in water.  Circumstantial evidence of shorelines can be seen today.

And in the southern hemisphere, in regions like Noachis Terra, we see unambiguous evidence of ancient flowing water.  Craters show obvious signs of erosion.  There are dried up lakes and rivers, and those rivers appear to have been fed by tributaries, which tells us it used to rain on Mars.

And there’s more.  Many Noachian-aged minerals and rock formations are most easily explained if we assume there was water.  In some cases, water is the only possible explaination.  Our Mars rovers have found mudstone, clay minerals, sedimentary rock… iron and magnesium carbonate… hematite, jarosite, and more!  Some of these minerals would have required a hot and slightly acidic environment, like you might find in a hot spring or near a hydrothermal vent.

We shouldn’t jump to conclusions.  After all, there’s still so much we don’t yet know about Mars, and new discoveries are being made all the time.  But I’m going to go ahead and call a spade a spade here: Noachian Mars sounds an awful lot like Arcean Earth, and it’s easy to imagine that whatever was happening on Arcean Earth (by which I mean LIFE!!!) must’ve also been happening on Noachian Mars.

However, the Noachian Period did not last long—a mere 400 million years.  Earth and Mars have had very different geological histories since then.  After the Noachian, Mars rapidly lost its internal heat, its atmosphere, and its oceans.  By the time of Earth’s Cambrian explosion, when complex, multi-cellular organisms really “exploded” onto the scene, Mars had fully transformed into the barren, inhospitable world we know today.

Modern day Mars has been trying really hard to get our attention and convince us that it might still support life.

And maybe that’s true.  During the Noachian, life had a great opportunity to get started on Mars, and it’s possible that some isolated remnant of a Noachian ecosystem has persisted to this day.  But in my opinion, it’s far more likely that we’ll find fossils left over from the Noachian Period (assuming we haven’t found some already).

Next time on Sciency Words A to Z, did you know there’s a deadly chemical in the air you breathe?  It’s called oxygen.