Life on ice

I'm currently reading planetary scientist Sarah Stewart Johnson's wonderful book The Sirens of Mars, about the search for signs of life on Mars (and other planets in the Solar System).  What strikes me whenever I read anything on this topic is that everything we've learned supports the contention that life is common in the universe.  (Not necessarily intelligent life; as I've dealt with before, that's another discussion entirely.)  As I learned from another great book I read a while back, Michael Ray Taylor's Dark Life: Martian Nanobacteria, Rock-Eating Cave Bugs, and Other Extreme Organisms of Inner Earth and Outer Space, every place we've looked on Earth -- however seemingly inhospitable -- we've found living things.  Fissures in rocks miles underneath the Earth's surface; deep-sea hydrothermal vents under crushing pressures and sky-high temperatures; brine ponds containing water many times the salinity of seawater; alkaline and acidic hot springs; chilly, pitch-dark caves with toxic air; anaerobic, sulfur-filled mud.  Teeming with life, all of them.

Not only that, but the building blocks of life are kind of everywhere.  When Stanley Miller and Harold Urey did their mind-blowing experiment back in 1953, it was unclear whether they had just happened on the right formula; they'd included their best guesses as to the constituents of the early Earth's atmosphere, and used artificial lightning as an energy source, and in short order they had organic compounds in enormous quantities.  It turned out, though, that the results had been not so much of a happy accident as an inevitability.  As long as you have (1) a reducing atmosphere (i.e. no free oxygen), (2) inorganic sources of carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur, and (3) some kind of an energy source, you end up synthesizing all twenty amino acids found in living things (plus some we don't use), DNA and RNA nucleotides, simple sugars, fatty acids, glycerol, and a host of other organic compounds.

In other words, every monomer you need to build an organism.  All from off-the-shelf inorganic chemicals and some kind of power source.

What became clear after Miller and Urey published their results is that the early Earth's seas -- and by extension, the seas of any planet with a reducing atmosphere and sufficient liquid water -- might be expected to be brimming with the building blocks of life.  This so-called "primordial soup" on Earth gave rise to primitive life in a relative flash, and there's no reason to expect the same wouldn't happen elsewhere.

What came as something of a shock, though, is that you don't even need warm, Earthlike conditions to generate biochemistry.  Not long ago, astrophysicists started finding the characteristic signatures of organic compounds in interstellar nebulae.  And just last week researchers at the University of Copenhagen announced that they'd discovered organic compounds in a cloud of gas, dust, and ice called Chameleon 1 -- one of the coldest, darkest places ever to be studied, located about six hundred light years away.

The Tarantula Nebula [Image courtesy of NASA, ESA, CSA, STScI, and the Webb ERO Production Team]

Detected by their spectroscopic fingerprints -- the characteristic frequencies of light they absorb from the ambient starlight -- these chemicals were located during a new study using the James Webb Space Telescope.  "With the application of observations, e.g. from ALMA [the Atacama Large Millimeter Array, which was also used in the study], it is possible for us to directly observe the dust grains themselves, and it is also possible to see the same molecules as in the gas observed in the ice," said Lars Kristensen, who co-authored the study.

"Using the combined data set gives us a unique insight into the complex interactions between gas, ice and dust in areas where stars and planets form," added Jes Jørgensen, who also co-authored.  "This way we can map the location of the molecules in the area both before and after they have been frozen out onto the dust grains and we can follow their path from the cold molecular cloud to the emerging planetary systems around young stars."

What this shows is that a great many of the compounds in the primordial soup may have formed before the coalescence of the Earth, and might already have been present when the seas formed.  "This study confirms that interstellar grains of dust are catalysts for the forming of complex molecules in the very diffuse gas in these clouds, something we see in the lab as well," said Sergio Ioppolo, another co-author.

Further evidence that biochemistry -- and almost certainly life -- is plentiful in the universe.

I wonder what life is like on other worlds.  Surely whatever it is, it's evolved into a host of forms completely different from what we have here, ones that have adapted to whatever the local conditions are.  Different sets of environmental challenges would generate new and innovative evolutionary solutions, as would a different set of one-off occurrences (such as the Chicxulub Meteorite collision that ended the supremacy of the dinosaurs and put us mammals on the pathway to pretty much running the place).  Now, take that diversity, those "endless forms most beautiful and most wonderful," as Darwin so trenchantly put it -- and multiply that by a million times.

That is what is very likely to be out there in the cosmos.

If I can be forgiven for ending a post with a quote by Carl Sagan two days in a row, the line he put in the mouth of his iconic character Ellie Arroway (from the book and the movie Contact) seems apposite: "If we're the only ones in the universe, it seems like an awful waste of space."

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The recipe for life

Back in my teaching days, I was all too aware of how hard it was to generate any kind of enthusiasm for the details of biology in a bunch of teenagers.  But there were a few guaranteed oh-wow moments -- and one that I always introduced by saying, "If this doesn't blow your mind, you're not paying attention."

What I was referring to was the Miller-Urey experiment.  This phenomenal piece of research was an attempt to see if it was possible to create organic compounds abiotically -- with clear implications for the origins of life.  Back in the early twentieth century, when people started to consider seriously the possibility that life started on Earth without the intervention of a deity, the obvious question was, "How?"  So they created apparatus to take collections of inorganic compounds surmised to be abundant on the early Earth, subject them to various energy sources, and waited to see what happened.

What happened was that they basically created smog and dirty water.  No organic compounds.  In 1922, Soviet biochemist Alexander Oparin suggested that the problem might be that they were starting with the assumption that the Earth's atmosphere hadn't changed much -- and looking at (then) new information about the atmosphere of Jupiter, he suggested that perhaps, the early Earth's atmosphere had no free oxygen.  In chemistry terms, it was a reducing atmosphere.  Oxygen, after all, is a highly reactive substance, good at tearing apart organic molecules.  (There's decent evidence that the pathways of aerobic cellular respiration originally evolved as a way of detoxifying oxygen, and only secondarily gained a use at increasing the efficiency of releasing the energy in food molecules.)

It wasn't until thirty years later that anyone tested Oparin's hunch.  Stanley Miller and Harold Urey, of the University of Chicago, created an apparatus made of sealed, interconnected glass globes, and filled them with their best guess at the gases present in the atmosphere of the early Earth -- carbon monoxide, methane, hydrogen sulfide, sulfur dioxide, water vapor, various nitrogen oxides, hydrogen cyanide (HCN), and so on.  No free (diatomic) oxygen.  They then introduced an energy source -- essentially, artificial lightning -- and sat back to wait.

No one expected fast results.  After all, the Earth had millions of years to generate enough organic compounds to (presumably) self-assemble into the earliest cells.  No one was more shocked than Miller and Urey when they came in the next day to find that the water in their apparatus had turned blood red.  Three days later, it was black, like crude oil.  At that point, they couldn't contain their curiosity, and opened it up to see what was there.

All twenty amino acids, plus several amino acids not typically found in living things on Earth.  Simple sugars.  Fatty acids.  Glycerol.  DNA and RNA nucleotides.  Basically, all the building blocks it takes to make a living organism.

In three days.

A scale model of the Miller-Urey apparatus, made for me by my son, who is a professional scientific glassblower

This glop, now nicknamed the "primordial soup," is thought to have filled the early oceans.  Imagine it -- you're standing on the shore of the Precambrian sea (wearing a breathing apparatus, of course).  On land is absolutely nothing alive -- a continent full of nothing but rock and sand.  In front of you is an ocean that appears to be composed of thick, dark oil.

It'd be hard to convince yourself this was actually Earth.

Since then, scientists have re-run the experiment hundreds of times, checking to see if perhaps Miller and Urey had just happened by luck on the exact right recipe, but it turns out this experiment is remarkably insensitive to initial conditions.  As long as you have three things -- (1) the right inorganic building blocks, (2) a source of energy, and (3) no free oxygen -- you can make as much of this rather unappealing soup as you want.

So, it turns out, generating biochemicals is a piece of cake.  And a piece of research at Friedrich Schiller University and the Max Planck Institute have shown that it's even easier than that -- the reactions that create amino acids can happen out in space.

"Water plays an important role in the conventional way in which peptides are created," said Serge Krasnokutski, who co-authored the paper.  "Our quantum chemical calculations have now shown that the amino acid glycine can be formed through a chemical precursor – called an amino ketene – combining with a water molecule.  Put simply: in this case, water must be added for the first reaction step, and water must be removed for the second...  [So] instead of taking the chemical detour in which amino acids are formed, we wanted to find out whether amino ketene molecules could not be formed instead and combine directly to form peptides.  And we did this under the conditions that prevail in cosmic molecular clouds, that is to say on dust particles in a vacuum, where the corresponding chemicals are present in abundance: carbon, ammonia, and carbon monoxide."

The more we look into this, the simpler it seems to be to generate the chemicals of life -- further elucidating how the first organisms formed on Earth, and (even more excitingly) suggesting that life might be common in the cosmos.  In fact, it may not even take an Earth-like planet to be a home for life; as long as a planet is in the "Goldilocks zone" (the distance from its parent star where water can exist in liquid form), getting from there to an organic-compound-rich environment may not be much of a hurdle.

That's still a long way from intelligent life, of course; chances are, the planets with extraterrestrial life mostly have much simpler organisms.  But how exciting is that?  Setting foot on a planet covered with life -- none of which has any common ancestry with terrestrial organisms.

I can think of very little that would be more thrilling than that.

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People made fun of Donald Rumsfeld for his statement that there are "known unknowns" -- things we know we don't know -- but a far larger number of "unknown unknowns," which are all the things we aren't even aware that we don't know.

While he certainly could have phrased it a little more clearly, and understand that I'm not in any way defending Donald Rumsfeld's other actions and statements, he certainly was right in this case.  It's profoundly humbling to find out how much we don't know, even about subjects about which we consider ourselves experts.  One of the most important things we need to do is to keep in mind not only that we might have things wrong, and that additional evidence may completely overturn what we thought we knew -- and more, that there are some things so far out of our ken that we may not even know they exist.

These ideas -- the perimeter of human knowledge, and the importance of being able to learn, relearn, change directions, and accept new information -- are the topic of psychologist Adam Grant's book Think Again: The Power of Knowing What You Don't Know.  In it, he explores not only how we are all riding around with blinders on, but how to take steps toward removing them, starting with not surrounding yourself with an echo chamber of like-minded people who might not even recognize that they have things wrong.  We should hold our own beliefs up to the light of scrutiny.  As Grant puts it, we should approach issues like scientists looking for the truth, not like a campaigning politician trying to convince an audience.

It's a book that challenges us to move past our stance of "clearly I'm right about this" to the more reasoned approach of "let me see if the evidence supports this."  In this era of media spin, fake news, and propaganda, it's a critical message -- and Think Again should be on everyone's to-read list.

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]

Life out of catastrophe

After yesterday's post about mysterious explosions in distant galaxies, today I want to look at a colossal explosion that happened much, much closer to home -- and may have jump-started life on Earth.

In a paper by Steven Benner of the Foundation for Applied Molecular Evolution in Alachua, Florida, presented at a conference last fall in Atlanta, we find out that there's geological evidence that early in Earth's history, there may have been a collision with an enormous object -- by some estimates, the size of the Moon -- that drastically altered the atmosphere.  4.47 billion years ago, only sixty million years after the Earth coalesced from the ring of planetary debris where it originated, it was struck so hard by planetoid that water molecules were ripped apart into oxygen and hydrogen, and superheated metallic debris was flung into the air and generated a torrential rain of molten iron.

Artist's conception of what the collision might have looked like from space

As the atmosphere (and everything else) cooled, the highly reactive oxygen bound to the iron, forming a thick layer of iron (and other metal) oxides that explains their prevalence in the Earth's crust today.  More interesting still is that the collision left behind the hydrogen in the atmosphere.  This created what is called a reducing atmosphere -- a collection of gases with an abundance of free electrons, essentially the opposite of what we have today (an oxidizing atmosphere, where oxygen and other electronegative elements mop up any available electrons, making organic matter and other reduced compounds fall apart).

The reducing atmosphere, Benner says, stuck around for two hundred million years, and it was during this time that the first organic compounds were formed.  This lines up neatly with the famous Miller-Urey experiment, where biochemists Stanley Miller and Harold Urey of the University of Chicago showed back in 1952 that in the presence of reducing gases and a source of energy, organic compounds formed readily, including DNA and RNA nitrogenous bases, amino acids, and simple sugars.

Benner believes that the critical one was RNA.  RNA is (as far as we know) unique in that it can not only replicate itself, it's autocatalytic -- it can catalyze its own reactions.  This pull-yourself-up-by-your-shoelaces ability is why a lot of scientists believe that the first genetic material was RNA, not the (currently) more ubiquitous DNA.  And Benner's theory about how the reducing atmosphere was generated explains not only how the building blocks of RNA could have formed, but why the Earth's atmosphere was reducing in the first place.

Benner believes the key is a set of biochemical reactions that involves repeated wetting and drying, along with interaction of the oxygen-free atmosphere with sulfur-containing gases released from volcanic eruptions.  He has demonstrated that in these conditions, formaldehyde -- CH₂O, one of the simplest organic compounds, would form "by the metric ton."  From there, reactions with the sulfur-bearing gases produced hydroxymethanesulfonate, which reacts readily to form glyceraldehyde (a simple sugar) and the four bases of RNA, adenine, cytosine, guanine, and uracil.

Once that happens, the autocatalytic ability of RNA means you're off to the races.  As Richard Dawkins pointed out in his tour-de-force The Blind Watchmaker, if you have two things -- an imperfect replicator, and a selecting mechanism -- you can generate order from disorder in the blink of an eye.  "[M]any experiments have confirmed that once RNA chains begin to grow, they can swap RNA letters and even whole sections with other strands, building complexity, variation, and new chemical functions," said science journalist Robert F. Service, writing for Science magazine.  "[T]he impact scenario implies organic molecules, and possibly RNA and life, could have originated several hundred million years earlier than thought.  That would allow plenty of time for complex cellular life to evolve by the time it shows up in the fossil record at 3.43 billion years ago."

This research not only confirms what Miller and Urey showed in their landmark experiment 67 years ago, but lines up beautifully with what is known from studies by geologists of the earliest rocks.  As for Benner, he's ready to put aside any doubt.  When Ramon Brasser, paleogeologist at the Tokyo Institute of Technology, laid out a timeline of the early Earth in his talk at the Atlanta conference, Benner asked him when the atmosphere would have likely dropped below a temperature of 100 C, the boiling point of water.  Brasser indicated a point about fifty million years after the impact with the planetoid.

"That's it, then!" Benner said excitedly, pointing to a spot at about 4.35 billion years ago on the timeline.  "Now we know exactly when RNA emerged. It's there—give or take a few million years."

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This week's Skeptophilia book recommendation is a little on the dark side.

The Radium Girls, by Kate Moore, tells the story of how the element radium -- discovered in 1898 by Pierre and Marie Curie -- went from being the early 20th century's miracle cure, put in everything from jockstraps to toothpaste, to being recognized as a deadly poison and carcinogen.  At first, it was innocent enough, if scarily unscientific.  The stuff gives off a beautiful greenish glow in the dark; how could that be dangerous?  But then the girls who worked in the factories of Radium Luminous Materials Corporation, which processed most of the radium-laced paints and dyes that were used not only in the crazy commodities I mentioned but in glow-in-the-dark clock and watch dials, started falling ill.  Their hair fell out, their bones ached... and they died.

But capitalism being what it is, the owners of the company couldn't, or wouldn't, consider the possibility that their precious element was what was causing the problem.  It didn't help that the girls themselves were mostly poor, not to mention the fact that back then, women's voices were routinely ignored in just about every realm.  Eventually it was stopped, and radium only processed by people using significant protective equipment,  but only after the deaths of hundreds of young women.

The story is fascinating and horrifying.  Moore's prose is captivating -- and if you don't feel enraged while you're reading it, you have a heart of stone.

[If you purchase the book from Amazon using the image/link below, part of the proceeds goes to supporting Skeptophilia!]