Unless you’ve been living under a rock — Earth or Martian — in the past month, surely you have heard about the Curiosity rover’s landing and early adventures on Mars.
The prospects for what the rover could find has many in the space community very excited, even though Curiosity is supposed to look for habitable environments, not life itself.
However, a couple of weeks ago, noted theoretical physicist Lawrence Krauss said he wouldn’t be surprised if we do find evidence of life on Mars.
In an interview with CNN, Krauss said it’s possible Martian life could have “polluted” Earth early in our planet’s history, giving rise to life as we know it today.
The big surprise (in finding life) would be if it weren’t our cousins. Because what we’ve learned is that material goes back and forth between the planets all the time. We have discovered Martian meteorites in Antarctica, for example, and it goes the other way around, and microbes certainly (can) survive the the eight-month voyage in a rock.
Though Krauss did not specify which meteorites in Antarctica he was referring to, he is most likely talking about ALH84001, which was found in 1984.
The meteorite shot to international prominence in 1996 when scientists, led by NASA’s David McKay, published an article in the journal Science saying there was evidence the meteorite showed “primitive bacterial life” from Mars. In particular, they used a high-power electron microscope and found formations that they said are consistent with those caused by bacterial life.
The team’s proclamation met with scientific skepticism. The Lunar and Planetary Institute’s Allan Treiman said even if it did show evidence of life, the rocks could have been contaminated by Antarctic life or by handling of the meteorite after it was found.
John Bradley, an adjunct professor at the Georgia Institute of Technology, took his skepticism a step further: “Unfortunately, there are many signatures in the fossil record here on Earth, and probably on Mars, that look very similar to bacterial signatures. But they are not unique to bacterial processes,” he said in an undated NASA page (most likely from 2001, since it references a meeting from that time) that was reportedly based on a SPACE.com story.
NASA revisited the sample in 2009 with more advanced equipment and argued that life was the most plausible explanation for the formations. In a paper published in Geochimica et Cosmochimica Acta, the authors rejected the alternate hypotheses of shock or heating affecting the meteorite based on their experiments.
That said, the 1996 announcement is still a long way from confirmation. Krauss’ interview is below. What do you think of his views of Martian life?
Lead image courtesy of NASA.
Elizabeth Howell (M.Sc. Space Studies ’12) is a contributing editor for SpaceRef and award-winning space freelance journalist living in Ottawa, Canada. Her work has appeared in publications such as SPACE.com, Air & Space Smithsonian, Physics Today, the Globe and Mail, the Canadian Broadcasting Corp., CTV and the Ottawa Business Journal.
proof being that grass and plants have that green alien color. Q.E.D.
I find it hard to have sympathy with Krauss’ point of view.
The people who built Curiosity said it was not going in search of life, but of signs that Mars might have had the conditions to support life. This is a sensible question to ask, and Curiosity may return a sensible answer. However, unless Mars hosts a form of life like on the Earth – vigorous life that creates accurate copies of itself efficiently – then we will probably go on thinking “we haven’t found something we recognise as life, but lit might be out there somewhere: neither yes nor no.
Okay, suppose we get dramatic results that convince us that we know whether life exists on Mars, and the answer is that it does. Then you have to decide whether Martial life is related to Earth life. For me, the really exciting answer is “no, it isn’t”, for that would mean that life had evolved independently on two consecutive planets. The less exciting answer is that there has been some cross-contamination, and we only had one life-giving event. The realistic answer would be that some chemical forms are more likely to produce life, and even if we find something similar on Mars and on Earth, this could be parallel evolution. We would have to find something completely different, but capable of competing with Earth life.
Finally, if there is life that is common to Mars and Earth (which is the combination of two unlikely assumptions) then we may not know which came first, as Earth’s active geology and life has removed a lit of evidence for what life might have been like four billion years ago or so, But, let us suppose of a third time that we can get a certain answer, then we could have Earth ‘infecting’ Mars, or vice-versa.
I doubt if we will have firm evidence that Krauss’ was wrong any time soon. It is currently an unproved special case (life known to have gone from Mars to Earth) of an unproved special case (life on Earth and Mars known to have a common ancestor) of an unproved possibility (life known to exist on Mars). And the evidence for this is one picture of some tubular thing after going through (how many?) Martian meteorites with an electron microscope. But we know there are rocks on Earth that have similar structures without life being involved. Krauss has picked a possible viewpoint supported by very little objective evidence. We don’t have to prove that Krauss is wrong: Krauss has to convince us that he is right. If he does that, then this is science: if he doesn’t then he is just playing to the gallery.
Whoo… sorry for the essay, folks, but that seems to have caught a nerve.
You raise valid points but in my opinion nobody seems to ask the other way around: “But we know there are rocks on Earth that have similar structures without life being involved” …can scientists really convince us that eg the ALH84001 putative microfossils are abiotic and if so why? Actualy I think the case is nobody knows yet – same goes for the Viking results: could be abiotic chemistry/could be biology with the strongest case for the latter by the Viking LR results. Over scepticism slows down scientific progress – no further life detection experiments or experiments to determine the nature of the Viking results for almost 40 years was the result on Mars. In my opinion planetary scientists would be stupid to not acknowledge the Viking results as having detected signs of extraterrestrial life if the MSL rover will confirm the presence of organics on Mars (the most important potential particular finding of MSL).
The ‘odds’ are with us! Given that there are giga-trillions of stars out thar, it’s absurd to think that we are the sole planet with life on it! Of course my pantheist attitude assumes that the entire universe is alive… perhaps even the stars themselves? So I am much more easily convinced there is life elsewhere. In more conservative religiosity, which includes the judeo-christian-islamic traditions, I feel that the precept that the Earth is the _center_ of the universe is actually quite silly and sadly archaic. The adherents of those ideologies have traditionally STOMPED on anyone who thought otherwise… even burned them at the stake! However gruesome our evolutionary history is, we are nevertheless moving forward. I say, DAMN the misanthropes, and full speed ahead!
Finding summertime methane above certain areas in the Martian atmosphere.. IS quite intriguing. Maybe, just maybe… there is life presently on Mars. GO life!
I tire of panspermia talk. Yes, it’s possible, yes it would be exciting if true… but it hardly helps nail down how life began in the first place, which is the real question.
If we’re going by panspermia, then an intelligent alien race could have visited the primordial earth and dumped its sewage receptacle out in a puddle thus bringing all future life to earth – and we’d never, ever know the truth.
Unless we eventually met the (other) descendants of that alien race, of course. 🙂
Agree with the problem that a panspermia theory only moves the problem to another planet and additionally, it means life must have arisen even closer in time to Big Bang, which seems less likely than it appearing on Earth 4 Bn years ago. What speaks in favor of a panspermia theory is the fact that as far as we know (deduced from all life being related, as far as we know, right?), life only arose once on Earth, not repeatedly throughout prehistory, which, if conditions for life arising on Earth are good, seems kind of strange.
Already Darwin realized he had to make a prediction for why the earlier hypotheses of no spontaneous generation of life were essentially correct as regards abiogenesis. He had independently come up with the proposal of “a warm little pond” (a so called “soup” theory) for the chemical evolution of the first cells.
This probably suggested his hypothesis here, which remains the generic one, that present life rapidly assimilate products of chemical evolution.
We now know that Earth has undergone a global transformation of its chemical state. It is now believed that the early Earth started out somewhat like Venus. A massive CO2 atmosphere was released from the mantle during and after crust formation, from its supply of carbon and oxides. Added to that, released hydrogen contributed to make the water we see today.
A mainly neutral atmosphere is producing organics at much lower rates than a reducing atmosphere, but any hydrogen excess and local reductive conditions around hydrothermal vents turns that around.
However, upper atmosphere hydrolysis of water and hydrogen escape to space vented any hydrogen excess in the first ~ 0.5 billion years. Sooner or later the increasingly neutral atmosphere would flip to an oxidative state, which is what happened. When that happens, abiotic production rates of organics hits rock bottom.
To sum up, as long as you have hydrothermal vents around, you retain a possibility for abiogenesis. But it is lower than the initial one, and current life extinguish any new abiogenesis attempts.
It is possible that early life saw repeated and concurrent abiogenesis attempts. A major hypothesis is that such attempts, or just one initially branching attempt, merged a community of disparate metabolic and/or cellular populations together until later a comprehensive genetic lineage appeared. (Or in some theories lineages, only sharing the genetic machinery.)
These hypotheses are often based on ideas of “rampant” horizontal genetic transfer. But as it turns out whole genome sequencing implies it wasn’t so rampant, at least at the time protein genes started to form. YMMV.
I think you are missing something important.
If panspermia is true, it is likely IMPOSSIBLE to “nail down” the orgin of life with only the Earth as a sample.
Neither the geologic nor biologic records here would help us.
This is not news. This is an off-hand comment from a theoretical physicist – who doesn’t work on the subject, and there is no real news. We are not one iota closer to knowing the answer due to educated guess of a physicist. One could have written this story years ago. His views are “tantalizing inconclusive”.
We certainly know of a lot of martian meteorites that has been ejected to migrate and end up on Earth, and it has been estimated ~ 250 kg/y of martian material ends up here today. And a smaller amount of Earth material ends up on Mars.
That said, there is little chance that they will travel directly, and ALH84001 is a test of that. It has been estimated it traveled in space ~ 15 Ma (million years).
Cosmic radiation (CR) will knock apart any nucleotide chains as freeze dried life lies dormant during that time. Any such life would also have to survive two consecutive shock impacts where the survivability of just one is microscopic [sic!].
Mars is a planetoid that got the jump on the more fully developed Earth by forming in ~ 3 Ma as opposed to a minimum 30 Ma. So what are the chances that life on Mars would have seeded Earth?
The Earth-Moon impact sterilized Earth. Then the incoming flow of martian meteorites would have to add up to a large likelihood for seeding in the average time for life formation. In theories of life involving vent formation, free cells would arise before the maximum lifetime of a vent, or ~ 0.1 Ma. That is estimated to be rather the expected time for massive parallel chemical evolution all over the planet.
So we have something like ~ 2*10^7 kg of martian material, since we are talking about a time before the Late Heavy bombardment amped up delivery rates. If cracks in those rocks would transport something like 1 ug cells for every kg, we would have ~ 2*10-3 kg of cells or ~ 2*10^13 cells at ~ 10^-12 g/cell for bacteria. We need a survivability of > 10^-14.
The survivability of cells for typical hypervelocity shock pressures of typically ~ 20-50 GPa is ~ 10^-4 – 10^-6. Independent ascent and descent shocks would therefore make a survivability ~ 10^-10. Survivability for cells under ~ 25 Ma of space travel due to CR is estimated as ~ 10^-6 for best case. Adding it all up we get a likelihood of ~ 10^-2 against life originating on Earth, from the likelihood of *one* surviving cell under the comparable time that Earth itself would originate it.
This is a *very* rough estimate based on averages. However I would expect the likelihood is lower, since these numbers are observed for modern, robust cells with a modern genetic machinery and good self-repair after damage. In any case, the numbers stack up against the idea.
As for ALH84001, I believe it has been noted that every feature of it has now a plausible abiotic explanation.
Of course a lot of this is similar to a debate over who is going to win the next football game. We really have to wait for the actual outcome. The prospects for life on Mars are better than zero, but in the end we have to see how the cards are dealt.
LC
To expand on ALH84001, the modern context is the paper of Brasier et al that put out a comprehensive critique of earlier finds of the “pattern search” type. I.e. it criticized, correctly and with a detailed analysis, finds that are based solely on finds that superficially looks like cellular structures but turns out to have a simple abiotic prediction. Having several competing theories makes ambiguous observations a test for all. [“A fresh look at the fossil evidence for early Archaean cellular life”, Brasier et al, Phil. Trans R. Soc. B 2006.]
Such pattern search was the earlier standard, especially used by Schopf et al who claimed many early fossils. Most or all of those have now been criticized or outright rejected by others, while in some cases the original work is still referenced to by the original researchers.
Note also that Schopf is a NASA advisor on astrobiology. We can see the ALH84001 work, or individual NASA researchers who regularly put out SEM work on meteorites claiming observations of cellular life (Hoover). Some of that follows the early paleontology work, which is not to that appears to me to be the current standard.
And of course the cross discipline astrobiology has its detractors among the “pure” sciences, especially among microbiologists it seems. So these works, and the recent arguable “arsenic life” claims, are a sore point. It is not NASAs wrongdoing by any means, but the problems are there.
I don’t understand why there is all this expectation of life arising on Mars anyway.
It may have had water bubbling and steaming among the lava for a short duration in it’s formation but it quickly cooled and has been cooling since. It was a hellish place that froze over, lost it’s tenuous atmosphere and never changed much other than periodic bombardments- which didn’t help matters. It’s frozen, arid, irradiated and near vacuum.
The conditions for life never got better only worse. In my opinion the most interesting place to even look would be in the region of ANY current geothermal activity. (are there any?)
What this article does make clear is that unless we find something crawling around and trying to eat the camera, we are only going to be privy to arguments of veracity and proof about it. As far as I can tell they are still going back and forth about Stromatolites even with sections under instuments in the lab.
This doesn’t make the mission less interesting one iota. The proof of concept of the landing system opens the entire planet to robotic missions.
I think that reality will be that life spontaneous spawns everywhere. But on most planets can’t survive long enough to evolve long time.