NASA’s Curiosity Rover Measures Intriguing Carbon Signature on Mars


After analyzing powdered rock samples collected from the surface of Mars by NASA’s Curiosity rover, scientists today announced that several of the samples are rich in a type of carbon that on Earth is associated with biological processes.

While the finding is intriguing, it doesn’t necessarily point to ancient life on Mars, as scientists have not yet found conclusive supporting evidence of ancient or current biology there, such as sedimentary rock formations produced by ancient bacteria, or a diversity of complex organic molecules formed by life.

“We’re finding things on Mars that are tantalizingly interesting, but we would really need more evidence to say we’ve identified life,” said Paul Mahaffy, who served as the principal investigator of the Sample Analysis at Mars (SAM) chemistry lab aboard Curiosity until retiring from NASA’s Goddard Space Flight Center in Greenbelt, Maryland, in December 2021. “So we’re looking at what else could have caused the carbon signature we’re seeing, if not life.”

This image shows the Highfield drill hole made by NASA’s Curiosity rover as it was collecting a sample on Vera Rubin Ridge in Gale crater on Mars. Drill powder from this hole was enriched in carbon 12. The image was taken by the Mars Hand Lens Imager on the 2,247th Martian day, or sol, of the mission.Credits: NASA/Caltech-JPL/MSSS.

In a report of their findings to be published in the Proceedings of the National Academy of Sciences journal on January 18, Curiosity scientists offer several explanations for the unusual carbon signals they detected. Their hypotheses are drawn partly from carbon signatures on Earth, but scientists warn the two planets are so different they can’t make definitive conclusions based on Earth examples.

“The hardest thing is letting go of Earth and letting go of that bias that we have and really trying to get into the fundamentals of the chemistry, physics and environmental processes on Mars,” said Goddard astrobiologist Jennifer L. Eigenbrode, who participated in the carbon study. Previously, Eigenbrode led an international team of Curiosity scientists in the detection of myriad organic molecules — ones that contain carbon — on the Martian surface.

“We need to open our minds and think outside the box,” Eigenbrode said, “and that’s what this paper does.”

The biological explanation Curiosity scientists present in their paper is inspired by Earth life. It involves ancient bacteria in the surface that would have produced a unique carbon signature as they released methane into the atmosphere where ultraviolet light would have converted that gas into larger, more complex molecules. These new molecules would have rained down to the surface and now could be preserved with their distinct carbon signature in Martian rocks.

Two other hypotheses offer nonbiological explanations. One suggests the carbon signature could have resulted from the interaction of ultraviolet light with carbon dioxide gas in the Martian atmosphere, producing new carbon-containing molecules that would have settled to the surface. And the other speculates that the carbon could have been left behind from a rare event hundreds of millions of years ago when the solar system passed through a giant molecular cloud rich in the type of carbon detected.

“All three explanations fit the data,” said Christopher House, a Curiosity scientist based at Penn State who led the carbon study. “We simply need more data to rule them in or out.”

Learn More:

With Mars Methane Mystery Unsolved, Curiosity Serves Scientists a New One: Oxygen

First You See It, Then You Don’t: Scientists Closer to Explaining Mars Methane Mystery

NASA’s Curiosity Rover Finds Clues to Chilly Ancient Mars Buried in Rocks

To analyze carbon in the Martian surface, House’s team used the Tunable Laser Spectrometer (TLS) instrument inside the SAM lab. SAM heated 24 samples from geologically diverse locations in the planet’s Gale crater to about 1,500 degrees Fahrenheit, or 850 degrees Celsius, to release the gases inside. Then the TLS measured the isotopes from some of the reduced carbon that was set free in the heating process. Isotopes are atoms of an element with different masses due to their distinct number of neutrons, and they are instrumental in understanding the chemical and biological evolution of planets.

Carbon is particularly important since this element is found in all life on Earth; it flows continuously through the air, water, and ground in a cycle that’s well understood thanks to isotope measurements.

For instance, living creatures on Earth use the smaller, lighter carbon 12 atom to metabolize food or for photosynthesis versus the heavier carbon 13 atom. Thus, significantly more carbon 12 than carbon 13 in ancient rocks, along with other evidence, suggests to scientists they’re looking at signatures of life-related chemistry. Looking at the ratio of these two carbon isotopes helps Earth scientists tell what type of life they’re looking at and the environment it lived in.

On Mars, Curiosity researchers found that nearly half of their samples had surprisingly large amounts of carbon 12 compared to what scientists have measured in the Martian atmosphere and meteorites. These samples came from five distinct locations in Gale crater, the researchers report, which may be related in that all the locations have well-preserved, ancient surfaces.

“On Earth, processes that would produce the carbon signal we’re detecting on Mars are biological,” House said. “We have to understand whether the same explanation works for Mars, or if there are other explanations, because Mars is very different.”

Mars is unique because it may have started off with a different mix of carbon isotopes than Earth 4.5 billion years ago. Mars is smaller, cooler, has weaker gravity, and different gases in its atmosphere. Additionally, the carbon on Mars could be cycling without any life involved.

“There’s a huge chunk of the carbon cycle on Earth that involves life, and because of life, there is a chunk of the carbon cycle on Earth we can’t understand, because everywhere we look there is life,” said Andrew Steele, a Curiosity scientist based at the Carnegie Institution for Science in Washington, D.C.

This mosaic was made from images taken by the Mast Camera aboard NASA’s Curiosity rover on the 2,729th Martian day, or sol, of the mission. It shows the landscape of the Stimson sandstone formation in Gale crater. In this general location, Curiosity drilled the Edinburgh drill hole, a sample from which was enriched in carbon 12.Credits: NASA/Caltech-JPL/MSSS

Steele noted that scientists are in the early stages of understanding how carbon cycles on Mars and, thus, how to interpret isotopic ratios and the nonbiological activities that could lead to those ratios. Curiosity, which arrived on the Red Planet in 2012, is the first rover with tools to study carbon isotopes in the surface. Other missions have collected information about isotopic signatures in the atmosphere, and scientists have measured ratios of Martian meteorites that have been collected on Earth.

“Defining the carbon cycle on Mars is absolutely key to trying to understand how life could fit into that cycle,” Steele said. “We have done that really successfully on Earth, but we are just beginning to define that cycle for Mars.”  

Curiosity scientists will continue to measure carbon isotopes to see if they get a similar signature when the rover visits other sites suspected to have well-preserved ancient surfaces. To further test the biological hypothesis involving methane-producing microorganisms, the Curiosity team would like to analyze the carbon content of a methane plume released from the surface. The rover unexpectedly encountered such a plume in 2019 but there’s no way to predict whether that will happen again. Otherwise, researchers point out that this study provides guidance to the team behind NASA’s Perseverance rover on the best types of samples to collect to confirm the carbon signature and determine definitively whether it’s coming from life or not. Perseverance is collecting samples from the Martian surface for possible future return to Earth.

Curiosity’s mission is led by NASA’s Jet Propulsion Laboratory in Southern California; JPL is managed by Caltech.Banner image: NASA’s Curiosity rover captured these clouds just after sunset on March 19, 2021, the 3,063rd Martian day, or sol, of the rover’s mission. The image is made up of 21 individual images stitched together and color-corrected so that the scene appears as it would to the human eye. Credits: NASA/JPL-Caltech/MSSS

By Lonnie Shekhtman
NASA’s Goddard Space Flight Center, Greenbelt, Md.Last Updated: Jan 18, 2022Editor: Svetlana Shekhtman

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Ron Long
January 19, 2022 2:40 am

Interesting. The image of the sample site looks like supergene carbonate filling cracks, most likely calcite, so I quickly read several articles about carbon isotope fractionation during supergene processes. It appears that C13 is less mobile than C12, and C12 is enriched in supergene carbonates. If the white material filling the cracks in the rock are not carbonates…never mind. Sooner or later the question of “life” on Mars will be answered, if pond scum constitutes life.

Bryan A
Reply to  Ron Long
January 19, 2022 5:21 am

The C12 cloud hypothesis is relatively easy to test. If the Carbon rained down from the Solar System passing through a cloud, then the same C12 signature would exist on the Moon at the same geologic time.

Smart Rock
Reply to  Ron Long
January 19, 2022 9:42 am

I agree that the fracture fillings look like calcite or dolomite, but not sure about a supergene origin. They are clearly brittle fractures and the host rock is said to be sandstone, so they are probably post-lithification fractures. I would guess they are a late-diagenetic feature.

Sandstones don’t typically have a lot of carbonate, so I wonder if the presence of what obviously looks like carbonate, was why they chose that site for their carbon isotope study. They have a whole array of analytical instruments, and could probably tell us what the mineralogy is.

I’m always amazed at how familiar those Martian rocks look. The photos could have been taken in any desert or Arctic island, here on Earth.

Reply to  Smart Rock
January 19, 2022 9:54 am

Yep… Apart from having much lower quartz content, Martian sedimentary rocks and sequences are stunningly Earth-like.

Regarding Martian carbonates, this is a good article:

If not for the climate change scam, I’d be tempted to join the AGU, just for the planetary geology papers.

Reply to  David Middleton
January 19, 2022 10:12 am

Yeah I use to be an AGI member but they have lost the ball with regards to anything climate. I agree it’s a good article.

Reply to  mandobob
January 19, 2022 10:47 am

It’s getting harder and harder to renew my AAPG and SEG memberships.

I almost did drop SEG. But, I’ve been a member of SEG for just over 40 years… I figured I’d stay in.

Reply to  David Middleton
January 19, 2022 11:45 am

Still have my AAPG. So fa they don’t seem to be too “woke”, so to speak 🙂

Reply to  David Middleton
January 19, 2022 12:14 pm

Oh well….AAPG gotta jump on that bandwagon I guess. So sad.

Ron Long
Reply to  David Middleton
January 19, 2022 1:01 pm

David, I dropped my SEG membership when they referred to Exploration Geologists as “Technicians”.

Reply to  Smart Rock
January 19, 2022 2:56 pm

Or on Devon Island.

Reply to  Ron Long
January 19, 2022 11:37 am


Joseph Zorzin
January 19, 2022 3:17 am

anyone who likes imagery from Mars be sure to check out the following YouTube site all in 4K

Steve Keohane
Reply to  Joseph Zorzin
January 19, 2022 5:48 am

About 15 years ago I had a large printer and took one of the 360° views of the Martian landscape and printed it out at 2.5′ X 18′, 300dpi. Made a great scene for my grandson’s room.

Peta of Newark
January 19, 2022 3:26 am

This is interesting, not to all of us tho, as it points directly at my long & oft asserted assertion that “The human animal cannot lie

Quote:”While blah blah doesn’t necessarily point to ancient life on Mars, blah blah blah such as sedimentary rock formations produced by ancient *bacteria*, or a blah blah formed by life.
(blahs added in an attempt to reduce wind and aid clarity)

See that, do you actually see that?
They say that bacteria are an essential for there to be Life On Anywhere, even if the bacteria are The Only Life

Thus and therefore, The Enquiring Mind tap tap tapping on this keyboard here & now *DEMANDS* to know:
Why humanity right now (and for the last 10,000+ yrs) is and has been hell-bent on destroying The Most Massive and Important reservoir of bacterial life on this Earth?
i.e. The soil, the dirt, the A Horizon or whatever you call it wherever your keyboard is.

In view of what the all the powerful bend-over and be s**gg*d senseless fawn, grovel, pray & obey, give them money NASA says:
What will happen when we complete our work of destroying all those bacteria – and filling the sky with CO2 as a consequence, a’la Mars?

We truly are in A Dark Age

It is nice that ‘squirrels’ can be relied upon to lighten the gloom, doncha think?

Reply to  Peta of Newark
January 19, 2022 3:55 am

“my long & oft asserted assertion that “The human animal cannot lie”

And yet politicians, media, sections of academia and even Nobel victim winners such as Michael Mann often do.

Reply to  fretslider
January 19, 2022 4:27 am

Therefore, they must not be human?

Reply to  Disputin
January 19, 2022 4:44 am

“my long & oft asserted assertion that “The human animal cannot lie”

Is brimming with wrongability

Reply to  Peta of Newark
January 19, 2022 6:50 am

Actually, we aren’t destroying the soil.

Reply to  Peta of Newark
January 19, 2022 7:10 am

I don’t share your circuitous pessimism. Bacteria aren’t necessarily essential to other forms of life. They are merely very simple forms that usually precede more complex forms. In that the more complex forms can benefit from the bacteria in symbiosis or other relationships is often common, however not essential.
To hyperbolically say that NASA’s goal is to destroy Martian bacteria is utterly non-sequitur.

Captain climate
January 19, 2022 3:40 am

Just dangling the possibility of life out there to get more funding. Let’s face it, the American public isn’t going to want to keep sending Mars rovers if it’s a dead planet and always has been.

Thomas Gasloli
Reply to  Captain climate
January 19, 2022 6:57 am

I agree. So little science, so much science fiction. Anyone with half a brain knows there was never is not now, never will be life on Mars.👽

Reply to  Thomas Gasloli
January 19, 2022 9:09 am

TG – Based on good science investigations over the past half of a century, has shown that Mars likely had significant liquid water present around 3- to 3.5-billion years ago and may still have large amount of water (as ice) just under the ground surface. As best we know, water is a key ingredient for life (among others) and given that Mars “cooled” or “evolved” earlier than the Earth there is the possibility that life (bacteria, virus, etc) evolved on Mars early in it’s history. So far the search results have been ambiguous but with tantalizing hints that life likely did exist on Mars sometime in the past. Keep in mind that although we have gained tremendous science knowledge about Mars through rovers and other observatories, we still have barely scratched the proverbial surface of the planet. Perhaps we have just not look in the right spot.

We know of no other life (dead or alive) in our solar system. The finding that Mars actually did have ancient life would be one of the greatest discoveries ever made. No “science fiction” here.

Captain climate
Reply to  Mandobob
January 19, 2022 11:10 am

Water is one of the most abundant substances in the universe, and no guarantee of life.

Reply to  Captain climate
January 19, 2022 12:05 pm

As Earthlings we know that water is one of the most important components for life as we know it. Does that translate to other words? Who knows. We do know that Mars at one time had plentiful liquid water and enough time to probably make a difference if Mars life was like Earth life (say over 500+ MYs). I agree no guarantee of life exists in in our solar system however, only the Earth and Mars are in the habitual zone, “Goldilocks zone” favored by planetary researchers. So looking for life (probably ancient) on Mars offers us one of our best opportunities for the existence of extraterrestrial life even if it is now extinct . No other planets or moons in our system really are reasonable candidates. Its true that some unique conditions could be made for some of Jupiter moons (Europa, for example) that might yield life (once again liquid water) but any real exploration of Jupiter moons is decades or greater away.

Reply to  Captain climate
January 19, 2022 12:17 pm

Liquid water does not appear to be abundant in the universe. Although some of the Jovian and Saturnian moons may have liquid water under their ice crusts.

On Earth, some form of life appears to be present wherever persistent liquid water is present. There’s only one example on Earth where there is abundant liquid water and no life at all.

While, evidence of past liquid water on Mars is no guarantee that life evolved there at some point in the past, it’s the best place to look for it. If present, evidence of past Martian life (fossils) will be found in its sedimentary rocks, particularly the shale (mudstone) formations. Curiosity has already documented many geological features in Gale Crater that are morphologically similar to fossilized stromatolites, lichens, algae, algal mats, etc.

However, until samples of those rocks can be brought back to Earth and physically examined, we won’t know if those examples are fossils or the result of abiotic processes. Even then, we might not know for sure… Science is never settled.

Reply to  David Middleton
January 20, 2022 6:42 am
Reply to  Yooper
January 20, 2022 2:18 pm

I saw that headline, but haven’t had time to read it yet.

Paul Penrose
Reply to  Thomas Gasloli
January 19, 2022 9:44 am

Nobody “knows” anything of the sort. You are, of course, entitled to your opinion, but to present it as knowledge is disingenuous at the very least.

Captain climate
Reply to  Thomas Gasloli
January 19, 2022 11:08 am

Notice there are 4 downvotes on a basic fact. By Apollo 13, no one cared anymore. Yet the next rover digging through rocks is supposed to gain interest?

Tom Abbott
Reply to  Captain climate
January 20, 2022 4:28 am

We don’t really have to worry about the American public losing interest in exploring Mars. And I’m not agreeing that is the case. But there are enough billionaires interested in the subject, to make it happen, whether the public is enthusiastic about it or not.

Reply to  Captain climate
January 19, 2022 8:24 am

What an absurd prediction.
How exactly is the existence of “life as we know it” a prerequisite for exploration and colonization? Life as we know it certainly doesn’t exist in space, but there we are. It certainly doesn’t exist on the moon, but we will within our lifetimes.
Such utterings are made by fearful homebodies. Let them inherit the earth. I’m going for the stars.

Captain climate
Reply to  Rocketscientist
January 19, 2022 11:11 am

The public doesn’t care what you consider to be reasons to explore. I’m all for pure research. But the NASA PR machine is sickening.

January 19, 2022 3:49 am

Now that NASA knows that rock samples could be riddled with Carbon I guess they’ll be leaving them in the ground… </sarc>

January 19, 2022 4:18 am

“All three explanations fit the data,”

I found this phrase especially refreshing, while wondering how it got past the propaganda department editors.

Reply to  dk_
January 19, 2022 5:39 am

They must be geologists! 😉

DD More
Reply to  David Middleton
January 19, 2022 11:27 am

David, as a geologist, did you note the passage, “geologically diverse locations in the planet’s Gale crater“?

What created the Gale Crater? Volcanoes or meteors come to mind for craters on earth.

If Gale was a ‘Ice Comet’ creation, would / could that change the Carbon signal that they found?

Reply to  DD More
January 19, 2022 11:54 am

Gale Crater and Jezero Crater are impact craters. Probably from large metallic or chondritic asteroid impacts about 4 billion years ago. Over the next few hundred million years, the craters were filled with fairly deep lakes. The evidence of fluvial (stream) and lacustrine (lake) erosion and deposition is extensive. By about 3-3.5 billion years ago, the lakes dried up and Mars’ sedimentary processes have largely been restricted to aeolian (wind-driven) processes.

Both craters are geologically diverse. There are basaltic igneous rocks & breccias related to impacts, conglomerate, sandstone, shale (mudstone) & carbonate rocks related to fluvial and lacustrine processes and sandstones & siltstones related to aeolian processes.

The carbon isotope anomalies probably aren’t related to the original impacts. Most likely they are related to the three processes discussed in the article. Although, we don’t even know what we don’t know about Mars. There could be other geochemical processes that haven’t been thought of yet.

Pop Piasa
Reply to  dk_
January 19, 2022 5:40 am

“We simply need more data to rule them in or out.”

Science never positively rules in, it only can rule out through observation.
These folks might need to learn from Popper and Feynman.

Reply to  Pop Piasa
January 19, 2022 8:13 am

The starting point in geology is Chamberlin’s Method of Multiple Working Hypotheses. Working hypotheses are different explanations that all fit the data. You work all the multiple hypotheses. Some are ruled out, some are ruled in, over time as more observations and data are collected and as methods of testing the hypotheses are refined. Some working hypotheses remain “on the bubble,” neither ruled in or out.

There rarely are “unique” solutions in geology.

Reply to  David Middleton
January 19, 2022 8:31 am

Enlightening. I’ve never heard this method ascribed to a particular individual or field. To me it was always just a part of the scientific method, akin to “not leaping to conclusions”.

Reply to  Rocketscientist
January 19, 2022 8:51 am

When you’re working on rock outcrops, it’s usually best to avoid leaping to anything… 😉

Reply to  David Middleton
January 19, 2022 8:55 am

The following is a modern reprise of T.C. Chamberlin’s famous paper on Multiple Working Hypotheses. Chamberlin’s paper is too long, too high-blown, and too sexist for modern students, but Chamberlin’s idea of multiple working hypotheses is, in my opinion, more important than ever (see Geology 1990 v. 18, p. 917-918.) If you want to generate paper copies, there’s also a PDF file. The text below was written in about 1990, was made available on-line in the mid-1990s, and was published in the Houston Geological Society Bulletin (v. 47, no. 2, p. 68-69) in October 2004 at the request of the editor of that publication.

T. C. Chamberlin’s “Method of Multiple Working Hypotheses”: An encapsulation for modern students

L. Bruce Railsback

Department of Geology, University of Georgia, Athens, Georgia 30602-2501 USA


Scientific study designed to increase our knowledge of natural phenomena can follow at least three different intellectual methods. These can be called the method of the ruling theory, the method of the working hypothesis, and the method of multiple working hypotheses. The first two are the most popular but they can, and often do, lead to ineffective research that overlooks relevant data. Instead, the method of multiple working hypotheses offers a more effective way of organizing one’s research.

Ruling Theories and Working Hypotheses

Our desire to reach an interpretation or explanation commonly leads us to a tentative interpretation that is based on relatively hasty examination of a single example or case. Our tentative explanation, as such, is not a threat to objectivity, but if we then begin to trust it without further testing, we can be blinded to other possibilities that we ignored at first glance. Our premature explanation can become a tentative theory and then a ruling theory, and our research becomes focused on proving that ruling theory. The result is a blindness to evidence that disproves the ruling theory or supports an alternate explanation. Only if the original tentative hypothesis was by chance correct does our research lead to any meaningful contribution to knowledge.

Seemingly less insidious is the working hypothesis. The working hypothesis, we are told, is a hypothesis to be tested, not in order to prove the hypothesis, but as a stimulus for study and fact-finding. Nonetheless, the single working hypothesis can imperceptibly degenerate into a ruling theory, and our desire to prove the working hypothesis, despite evidence to the contrary, can become as strong as the desire to prove the ruling theory.

Multiple Working Hypotheses

The method of multiple working hypotheses involves the development, prior to our research, of several hypotheses that might explain the phenomenon we want to study. Many of these hypotheses will be contradictory, so that some, if not all, will prove to be false. However, the development of multiple hypotheses prior to the research lets us avoid the trap of the ruling hypothesis and thus makes it more likely that our research will lead to meaningful results. We open-mindedly envision all the possible explanations of the phenomenon to be studied, including the possibility that none of explanations are correct (“none of the above”) and the possibility that some new explanation may emerge.

The method of multiple working hypotheses has several other beneficial effects on one’s research. Careful study often shows that a phenomenon is the result of several causes, not just one, and the method of multiple working hypotheses obviously makes it more likely that we will see the interaction of the several causes. The method also promotes much greater thoroughness than research directed toward one hypothesis, leading to lines of inquiry that we might otherwise overlook, and thus to evidence and insights that single-minded research might never have encountered. Thirdly, the method makes us much more likely to see the imperfections in our knowledge and thus to avoid the pitfall of accepting weak or flawed evidence for one hypothesis when another provides a more elegant solution.

Possible Drawbacks of the Method

The method of multiple working hypotheses does have drawbacks. One is that it is impossible to express multiple hypotheses simultaneously, and thus there is a natural tendency to let one take primacy. Keeping a written, not mental, list of our multiple hypotheses is often a necessary solution to that problem.

Another problem is that an open mind may develop hypotheses that are so difficult to test that evaluating them is nearly impossible. An example might be where three of our hypotheses are testable by conventional field work, but a fourth requires drilling of a deep borehole beyond our economic resources. This fourth hypothesis need not paralyze our research, but it should provide a reminder that none of the first three need be true.

A third possible problem is that of vacillation or indecision as we balance the evidence for various hypotheses. Such vacillation may be bad for the researcher, but such vacillation is preferable to the premature rush to a false conclusion.

An Example

The field discovery of a breccia provides an excellent example of the application of the method of multiple working hypotheses. A breccia may form in many ways: by deposition as talus, by collapse after dissolution of underlying evaporites or other soluble rocks, by faulting, by bolide impact, or by other means. Each of the possibilities can be supported by various field evidence, for which we could look if we were evaluating all these hypotheses. However, if we chose just one hypothesis, we might ignore other evidence more clearly supportive of a different hypothesis. For example, if we hypothesized that our breccia was the result of cataclasis during faulting, we might find that the breccia occurred along a fault. We would then accept our single hypothesis and quit looking for additional information. However, if we were using multiple working hypotheses and looked for evidence supporting or disproving all our hypotheses, we might also notice that the breccia was localized in a circular pattern along just one part of the fault. Further examination might show that it was accompanied by shatter cones. Armed with this additional information, we would be more inclined to an interpretation involving an impact that was by chance coincident with a fault. By looking for evidence supportive of a variety of hypotheses, we would have avoided an incorrect interpretation based on coincidence.


In using the method of multiple working hypotheses, we try to open-mindedly envision and list all the possible hypotheses that could account for the phenomenon to be studied. This induces greater care in ascertaining the facts and greater discrimination and caution in drawing conclusions. Although our human tendencies lead us toward the method of the ruling theory, the method of multiple working hypotheses offers the best chance of open-minded research that avoids false conclusions.

T.C. Chamberlin and the method of multiple working hypotheses

The geologist Thomas Chrowder Chamberlin (1843-1928) was president of the University of Wisconsin, director of the Walker Museum at the University of Chicago, president of the American Association for the Advancement of Science, and the founder and editor of the Journal of Geology.

Chamberlin read his paper on “The method of multiple working hypotheses” before the Society of Western Naturalists in 1889, and it was published in Science in 1890 and the Journal of Geology in 1897. It was reprinted in several journals during the subsequent seventy years.

This is a short modern encapsulation of some of the ideas in Chamberlin’s original paper, and it should not be considered an adequate substitute for the original paper. This encapsulation is based on a version of the original paper republished in Science in 1965.

Chamberlin, T.C., 1890, The method of multiple working hypotheses: Science (old series) v. 15, p. 92-96; reprinted 1965, v. 148, p. 754-759.

Chamberlin, T.C., 1897, The method of multiple working hypotheses: Journal of Geology, v. 5, p. 837-848.

To a web-based copy of Chamberlin’s paper (apparently from the 1965 reprint)

Back to Railsback’s main page

Back to the UGA Geology Home Page

L. Bruce Railsback

Pop Piasa
Reply to  David Middleton
January 19, 2022 9:05 am

Thanks David, it’s always a good day to learn.

Reply to  Pop Piasa
January 19, 2022 9:43 am

comment image

Reply to  Rocketscientist
January 19, 2022 10:16 am

Unless you need some exercise 🙂

D. J. Hawkins
January 19, 2022 8:24 am

NASA is so chary of making any bold claims regarding evidence of life on Mars, but can’t wait to regale us with the latest climate catastrophe prognostication on far flimsier evidence. Go figure.

Reply to  D. J. Hawkins
January 19, 2022 9:52 am

Climate science is overwhelmingly politicized; Mars science is not. That is the difference.

Steve Reddish
January 19, 2022 8:45 am

Since C12 constitutes 99% of all carbon on Earth, how could life NOT be composed primarily of C12?

Reply to  Steve Reddish
January 19, 2022 10:08 am

It is. WHere did you see it’s not?

Steve Reddish
Reply to  Matheus
January 19, 2022 3:58 pm

I was responding to the article that said: “scientists today announced that several of the samples are rich in a type of carbon that on Earth is associated with biological processes.”
That statement only means something if Earth life had another carbon option.

Reply to  Steve Reddish
January 19, 2022 11:20 pm

It is loosely worded. More precisely, the samples are enriched in C12. That is, the ratio C12/C13 is higher in samples associated with life than abiotic samples.

Steve Reddish
Reply to  Mactoul
January 20, 2022 8:51 pm

On Earth, the enrichment of C12 is miniscule because C13 is almost unavailable. Abiotic C12= 98.9%.
C4 plants are 99.21% C12, C3 plants are 99.24% C12.
That is not a difference that would indicate life is causing C12 enrichment on Mars, since the C12/C13 ratio on Mars is so different.

Rick C
January 19, 2022 8:53 am

Just curious as I don’t know the answer, but how would the lack of a magnetic field affect the formation of carbon isotopes on Mars? Is it possible that the C12:C13:C14 ratios observed are not just the natural result of a very different radiation exposure history?

Reply to  Rick C
January 19, 2022 10:20 am

On Earth, with the exception of C14, I believe that the overwhelming bulk of carbon 12 and 13 where formed in supernovae although biological process have modified the overall percentages that we see in the biosphere.

Reply to  mandobob
January 19, 2022 10:25 am

I forgot to clarify that the “star explosion” events would decide the overall percentages of C12 and C13 in our solar system. So the ration should be very similar on Mars baring biological modification. On Earth C14 is created, in part, by cosmic ray interaction with nitrogen in the atmosphere. I’m not so sure about Mars

Steve Reddish
Reply to  mandobob
January 19, 2022 4:07 pm

Are there non-biogenic caches of carbon that are higher in C13% than is found in the biosphere? I thought the Earth as a whole was 99% C12.

Steve Reddish
Reply to  Steve Reddish
January 19, 2022 5:19 pm

By digging further, I discovered a can of worms. It appears the overall ratio of C12 is quoted at 93%, but nearly everything measured has a much higher ratio of C12, including carbonatites. I could not find how that 93% C12 was derived.
Surprisingly, placer diamonds have one of the highest C12 ratios, suspected to be due to contamination…contaminated by what, or how a diamond can be contaminated once on the surface – crickets.
Although everyone agrees that plants preferentially select C12, no one suggests where the C13 is accumulating.

Reply to  Steve Reddish
January 21, 2022 6:41 am

Not sure where the C12 abundance of 93% is from but the abundance is much closer to 99% (98.93%). Diamonds are not one of my specialties; I work with oil & natural gas source rock and forensics. I believe the “contamination” may refer to incorporation of surface carbon into the lower crust/upper mantle through plate tectonics like processes that alter the expected or “normal” diamond carbon ratios. I’ll see if I can find a good reference to post. Diamonds are their own special cases of “weird”.

The enrichment of C13 is on a very small scale. Bacteria and plants and some nonbiological processes do show C13 isotope fractalization effect due to the preferential use of C12. I would not characterize the enrichment as accumulation and I hope my earlier posts did not suggest that.

Reply to  Steve Reddish
January 21, 2022 6:14 am

I’m not sure what you mean by “non-biological caches” but most carbon on earth is C12 (as you noted; C12 natural abundance 98.93 %, C13 abundance 1.07%). The very small percentage of C13 can be enriched by biological (mostly bacterial) processes that favor usage of C12 and resulting in enrichment of the C13 isotope (C12 to C12 chemical bonds are easier to break than C13 to C13 bonds). Admittedly this enrichment is relatively minor but is measurable and often a very good diagnostic tool when investigating oil and natural gas source rocks, biological sciences (food web evaluation), archology (ancient diets and agriculture), forensics, food industry (food adulteration), and sports regulation (performance enhancing drugs).

January 19, 2022 8:57 am

Seem like the quest has moved from searching for “life as we know it” to “bacteria as we know them” to “evidence of long dead biomarkers”. Sooner or later the bar will be set low enough to justify something scientific, instead of governments financing sexy stuff to show off their technical prowess.

Michael S. Kelly
January 19, 2022 2:16 pm

I described this article to my wife, and her response was “can’t they just wait a couple of years and ask Musk about it when he gets there?”

Seriously, though, this really is fascinating. Thanks for posting it.

michael hart
January 20, 2022 1:24 am

Put the idea out to the media by (correctly) denying it as a probable explanation.
Are they being half-way honest, or half-way dishonest?

Tom Abbott
January 20, 2022 3:42 am

From the article: ““We simply need more data to rule them in or out.””

Too bad alarmist climate scientists don’t have the same attitude.

Pat Frank
January 20, 2022 3:56 pm

Low temperature chemistry would also favor C-12. Detection of a large chiral excess would be strong evidence of life.

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