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Life, Unbounded

Life, Unbounded


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Maybe Mars Seeded Earth’s Life, Maybe It Didn’t

The views expressed are those of the author and are not necessarily those of Scientific American.


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Is this our ancestral home? (NASA/JPL)

This week a major geochemistry conference heard an argument for life on Earth having originated on Mars, but does this hold up to scrutiny?

The idea that a young Mars, some four billion years ago, was a far more hospitable and temperate place is not particularly controversial – although it is certainly not understood in any great detail. Now, at the annual Goldschmidt conference on geochemistry, the notion that it was Mars, not the Earth, that was the better place for life’s origins has been getting some attention. Indeed, as reported in this piece at BBC News, it sounds like there might be quite a robust case for martian beginnings.

The new argument, in a nutshell, is that young Mars had a more oxygen-rich atmosphere than Earth did 4 billion years ago, and was drier. This would have resulted in a different mineralogical surface environment, one that could have provided a catalyst for the assembly of key RNA molecules and all the biotic chemistry leading to life as we know it. Subsequent asteroid impacts on Mars would have spewed chunks of rock into space, carrying life (presumably in microbial form) through the solar system and onto the surface of a youthful Earth.

The transfer of life is certainly not a new idea. We know that pieces of Mars end up on the Earth, many are found in Antarctica where ice flow and exposure gathers and reveals them to keen human eyes. And we know that four billion years ago the rate of asteroid impact on the inner worlds of the solar system was significantly higher than it is today, part of the tailing off of planetary assembly and orbital evolution. Recent experiments and studies of what survives passage down through Earth’s atmosphere certainly suggest that viable organisms could make it, and impact driven material could have fast transit times through interplanetary space.

However, one problem lies in our understanding of the steps between basic molecules on a planet’s surface and the formation of a complex broth of RNA and proteins that could lead to cell structures and DNA. The hypothesis put forward at Goldschmidt rests on the idea that there must have been an inorganic, mineral catalyst to encourage basic molecules to assemble into the first RNA structures. Specifically, these were minerals built around boron and oxidized molybdenum, minerals that would have probably dissolved away in Earth’s early oceans, or simply not existed, but could have fared much better on Mars.

But the truth is that our theories about these first steps are themselves hotly contested. For example, other laboratory work (such as this study reported in Nature in 2009) indicates that other, common, catalysts (stuff like manganese or magnesium compounds, also sometimes helped along by ultraviolet light) can set in motion complex chemical networks that very naturally pop out the sort of stuff that’s going to make RNA, and even rudimentary cell membrane structures.

In other words, the precise nature of Earth’s early geo-chemistry might not be quite as critical, nor might that of Mars.

Another problem is that this idea assumes young Mars was significantly less wet than young Earth – or else stuff like the boron compounds would have dissolved and dispersed to useless concentrations there too. Except we know that ancient Mars had transient and perhaps even long-term liquid surface water, it was a far wetter place than it is now.

It’s also not clear that RNA is actually the only pixie dust on the road to life. The common emphasis on making RNA comes in part from the concept of an ‘RNA-world‘, a precursor chemical universe where self-replicating and catalyzing RNA molecules operated before being ‘replaced’ by the modern DNA, RNA, and protein world. But not everyone agrees that this works, at least not in a pristine form. Early RNA may have operated within a more complex mess of other molecules. And there are suggestions that RNA is actually more of an evolutionary outcome – the winner in a stew of other polymers. A great discussion of some of this is here.

So, did Mars seed life on Earth? We simply don’t know. However, by exploring the possibility we certainly stand to gain information from the fact that young Earth and young Mars probably were rather different – chemically and environmentally. Two natural test-tubes rather than one.

And there’s an even wilder possibility that I’ll throw out here for fun; although it’s entirely unsubstantiated at the moment. Perhaps, just perhaps, the to-and-fro of small chunks of material between these planets itself played a role in stirring the pre-biotic chemical pots of both worlds…

Caleb A. Scharf About the Author: Caleb Scharf is the director of Columbia University's multidisciplinary Astrobiology Center. He has worked in the fields of observational cosmology, X-ray astronomy, and more recently exoplanetary science. His latest book is 'Gravity's Engines: How Bubble-Blowing Black Holes Rule Galaxies, Stars, and Life in the Cosmos', and he is working on 'The Copernicus Complex' (both from Scientific American / Farrar, Straus and Giroux.) Follow on Twitter @caleb_scharf.

The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. dhughes 2:51 pm 08/29/2013

    Everyone knows men are from Mars and women are from Venus ;>)

    Link to this
  2. 2. American Muse 9:56 pm 08/29/2013

    Life on Earth probably began on Earth, not on Mars: if you hear hoof-beats in the distance, it is more likely to be a horse than a zebra.

    Link to this
  3. 3. Happy Hal 12:05 am 08/30/2013

    When the planet which formed the Asteroid Belt, blew up, it quite likely pushed pieces of it’s own mass to Mars , Europa, Earth and Venus, and to other moons and planets, as well.

    Link to this
  4. 4. Lenedwin 2:54 am 08/30/2013

    I don’t normally use expletives but, honestly, what a load of bollocks. It’s time we spent science grants on deserving researchers not idiot daydreamers.

    Link to this
  5. 5. Torbjörn Larsson, OM 5:31 am 08/30/2013

    I have a huge respect for Benner after the “arsenic life” debacle, as he pointed out how unfeasible and unevidenced the hypothesis was. But this is an old idea of his: “In point of fact, I happen to believe that molybdenum is essential for life, and molybdenum is much more scarce than either silicon or carbon. Boron might also be essential to life, and that is still less abundant.” (2006, http://www.spacedaily.com/reports/Debating_The_Boundaries_Of_Life_999.html ) And it haven’t panned out well what I know.

    - Boron is supposed to stabilize the ribose in RNA under salty (ocean) conditions. But before it was found in martian meteorites it was only known from Earth: “Boron is commonly found in clay sediments found on Earth.” [ http://www.natureworldnews.com/articles/2376/20130611/martian-meteorite-shows-tpresence-boron-helps-build-rna.htm ] And today we have evidence that ribose and the nucleotide bases is stabilized, and stabilizes, the lipids that was produced in the environment of early protocells. [Don't have the ref handy.]

    - Molybden I know less about, but googling the first poster describes how molybden was plentiful and presumably of the same oxidation state in the early Archean as today: “We suggest the geochemical cycle of Mo during the Archean-Paleoproterozoic time was essentially the same as today: Mo-bearing minerals were quantitatively oxidized during weathering, dissolved Mo was transported to the oceans, and it was fixed by C_org and sulfide S in locally anoxic marine environments.” [ "MOLYBDENUM GEOCHEMICAL CYCLE IN THE ARCHEAN", Yamaguchi, 2002 Denver Annual Meeting ; https://gsa.confex.com/gsa/2002AM/finalprogram/abstract_44043.htm ] The concentration of organics under the Hadean was presumably diluted outside of alkaline hydrothermal vents. They may have gummed up some surfaces, but not all.

    - We do know the Hadean had weathered (continental) crust. [Ushikubo et al 2008, "Lithium in Jack Hills zircons: Evidence for extensive weathering of Earth's earliest crust" http://www.geolog...008.pdf ; HT: barakn]

    In sum, the 3 proposed tests for conditions under the hypothesis all falls. Meaning the likelihood for local abiogenesis seems to have been good enough on Earth. Transpermia remains the less likely pathway, an easy enough estimate from known experiments. (But too long to cover here.)

    Link to this
  6. 6. Torbjörn Larsson, OM 5:37 am 08/30/2013

    @American Muse: Indeed! And when I modeled the transpermia rate vs the abiogenesis rate from recent estimates and observations, I found that transpermia came up short. Even as an existing tramway of protocellular populations, its likelihood is lower than local production rates. (But it takes a few thousand words to go through; another time perhaps.)

    @Happy Hal: We know that debris rings, and specifically the Asteroid Belt such, is not products of planets but of protoplanetary disks.

    @Lenedwin: What can be stated without evidence can be dismissed without evidence. But as it happens you describe your own comment well. =D

    Link to this
  7. 7. Jerzy v. 3.0. 6:46 pm 08/30/2013

    Another possible place is Venus. Actually, I am a fan of the idea that microbes live in Venutian cloud layer now – if they can hibernate when being periodically swept into the super-hot lower atmosphere, they can live fine. Earth extremophiles can survive in clouds, drought and acidic conditions.

    Curious is, that conditions on early Mars and Venus are just casually mentioned. I think that that possible Earth-like conditions on the other planets would be extremely important topic.

    Link to this
  8. 8. Postman1 8:53 pm 08/30/2013

    Caleb’s last paragraph is the one to think about. If Earth and Mars were tossing RNA, bacteria and whatever else to and fro, what was being passed to all the other environments in our system? Europa, Titan, Venus, etc? Hopefully we can someday find out.

    Link to this
  9. 9. Plain-2009 10:44 pm 09/3/2013

    Ah, you guys have sense of humor!
    I was very attracted by he name of the article.
    The idea that life came from Mars seems too farfetched an idea, indeed. But it very well could be.
    If there is certain evidence the idea should be thoroughly researched, anyway.
    The code to make RNA,and DNA and other complex molecules must be, somehow, somewhere written in the books of Nature.
    Probably life has been re-invented beginning from basic building blocks many times in the history of the Universe.
    May be it can even follow different paths.Creating different creatures.
    It is fascinating a Universe with no-beginning and no-end.
    But there is no reason to believe life has not been jumping from one planet to another or from one place of the Universe to another.
    If life was created once it can be created twice.

    Link to this
  10. 10. AnnaHarper 4:17 am 01/27/2014

    Such an exciting theory space debris as the source of life on earth. http://blogs.scientificamerican.com/life-unbounded/2013/08/29/maybe-mars-seeded-earths-life-maybe-it-didnt/

    Link to this
  11. 11. AnnaHarper 4:28 am 01/27/2014

    If you take a look at Caleb ( the author’s ) twitter feed you’ll see he is discussing this article quite often.

    Logged in as : https://www.facebook.com/steroidsuk

    Link to this
  12. 12. JaneMonk 3:20 pm 01/30/2014

    hopefully they can put a person on mars during my lifetime and find something really exciting there.

    Logged in as : steroids

    Link to this

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