We've Been Looking for Ourselves
The only mineralogist in the room, and I kept thinking about crystals.
Act 1: The Room
There is a specimen of apatite in my office at the Natural History Museum of Los Angeles County that I have been thinking about for over a year. It sits in a drawer with six others — same mineral, different histories — and I keep coming back to it because it is, in a precise and literal sense, the same mineral that is in your bones right now. Same formula. Different record.
I spent a week at Caltech in January 2024 arguing about what life is. Not philosophically. Practically. There were a little over thirty of us, funded by the Keck Institute for Space Studies, trying to answer a question that sounds simple until you actually try to answer it: how do you build an instrument to find life on another planet when you’re not entirely sure what life looks like?
I was the only mineralogist in the room. Nobody thought that was strange. I did.
The workshop was built around a question that has haunted planetary science for fifty years. In 1976, NASA landed two robotic spacecraft on the surface of Mars — the Viking landers, the most sophisticated machines humanity had ever sent to another planet. Their primary mission was not geology or weather or photography, though they did all of those things. Their primary mission was to find out whether anything was alive.
They ran the first — and still only — direct life-detection experiments ever conducted on another planet. The instruments worked flawlessly. The data came back clean. And then scientists spent the next fifty years arguing about what it meant.
That ambiguity is not a failure. It is the most honest scientific outcome possible. We built the best instruments we had, asked exactly the right questions, and the universe handed us a result we didn’t yet have the framework to interpret. Fifty years of better science followed directly from that unresolved result. That is what a good experiment does.
What Viking revealed, with extraordinary precision, was the shape of the problem. The Martian soil produced chemical signals that looked, in some ways, like the signals living things produce. And in other ways, didn’t. Was it life? Was it chemistry? We still don’t have a definitive answer.
I kept thinking about this in that room at Caltech. Not because of the biology. Because of the rocks.
I was in that argument. I helped shape what each category required. And the whole time, I kept drawing.
Not notes, exactly. More like a diagram I couldn’t stop refining — three overlapping circles on a iPad, with percentages at each intersection and a phrase scrawled underneath: Depth ≈ Time.
The people in that room were thinking about organisms. I was thinking about the archive those organisms leave behind. By the end of the week, I was certain those were the same problem — and that nobody in the room fully understood why.
Act 2: What Minerals Remember
Here is something most people don’t know about rocks: they remember.
Not the way organisms remember — not through neurons or behavior or instinct. But through structure. The way a crystal grows, the trace elements it incorporates, the defects locked into its lattice, the fluid trapped inside it when it formed — all of that is a record. A mineralogist reading a crystal is reading a document. The question is always: a document of what?
This is what I wrote under Metabolism on my diagram: Depth ≈ Time.
In biology, time runs through genealogy. You understand the past by tracing who descended from whom, how long the evolutionary clock has been running. In mineralogy, time is stratigraphy. Depth is time. The further down you drill into the earth, the further back you read. Each layer is a page. Each mineral in that layer is a sentence.
This is not a metaphor. It is how the geological record actually works. One of the concrete outcomes of that Caltech workshop was a mission concept built around exactly this idea: drill into the Martian subsurface, retrieve a vertical record of rock and salt and ancient brine, and read it layer by layer. When we drill a core sample from the Martian subsurface — something that mission concept is designed to do — we are not just collecting rock. We are collecting a physical archive of everything that happened in that place, at that depth, at that moment in planetary history. Temperature. Chemistry. Whether liquid water was present. Whether something was consuming that water and leaving waste behind.
A biologist looks at that core and asks: is there life here? A mineralogist looks at the same core and asks: what has this rock been through, what did it record, and can we trust what we’re seeing? Those are different questions. You need both.
Mineralogists have been part of Mars missions before — reading the mineralogy of the surface, identifying what the rocks are made of, characterizing the chemistry. That work is essential and it has been done well. But the specific question of life detection — designing the experiments, setting the burden of proof, deciding what counts as a biosignature and what doesn’t — has been largely a conversation between biologists, chemists, and engineers. The person trained to recognize when a mineral is mimicking life, or to know what a mineral record can and cannot preserve, has not always had a seat at that particular table. That Caltech workshop was one of the first times I felt the gap closing.
This matters because of what minerals actually do. Not just record. Preserve. Transform. And sometimes, deceive.
But the archive doesn't start at the moment life appears. The mineral record predates biology entirely — and the more you read it, the more you realize it didn't just witness life's beginning. It built the room.
Act 3: The Answer
Every serious scientific hypothesis about how life began on Earth involves minerals.
Not as background. Not as scenery. As the mechanism.
The leading hypothesis for life’s origin centers on hydrothermal vents on the ancient ocean floor — places where hot, mineral-rich water poured through cracks in the rock, creating chemical gradients across iron-sulfur mineral surfaces. Those gradients are thought to have driven the first proto-metabolic reactions. The chemistry of life didn’t happen in open water. It happened at the interface between water and rock.
Another hypothesis centers on clay mineral surfaces — thin, charged sheets of aluminosilicate that could have provided the ordered template that early RNA-like molecules needed to copy themselves. Without the clay, no copying. Without copying, no heredity. Without heredity, no evolution. Without evolution, no life.
A third hypothesis centers on evaporite minerals — salts that form when water evaporates. As ancient shorelines dried and rewet in cycles, organic molecules concentrated on evaporite surfaces, polymerized, and eventually crossed some threshold we don’t fully understand into something we would recognize as alive.
In all of these, minerals are not the stage. They are the actor. Life didn’t emerge despite the mineral world. It emerged through it.
And this relationship didn’t end at the origin. It continued. When organisms die, minerals preserve them. When microbial communities alter their environment, minerals record it — in isotopic signatures, in oxidation states, in the specific crystal habits that only form under biological influence. The entire fossil record is, at its core, a mineral record. Everything we know about the history of life on Earth we know because minerals remembered it.
This is why minerals are the answer to the life detection problem. The biosignatures we’re looking for on Mars — the chemical traces that would tell us something once lived there, or still does — will be preserved in minerals. Evaporites. Fluid inclusions. Clays. The archive is mineral. The evidence, if it exists, is mineral. The medium through which we must read the past is mineral.
Which brings me to the problem.
Act 4: The Obfuscation
Here is the part that took me years to say out loud: the same properties that make minerals the answer also make them the noise. A mineral that preserves biological chemistry does so because it forms stable structures from the same elements, under the same conditions, that life requires. That's not a coincidence. It means that every mineral capable of holding the evidence of life is also capable of producing something that looks exactly like it. The archive and the counterfeit are made of the same stuff.
In 1996, a team of NASA scientists announced that they had found evidence of ancient life in a Martian meteorite.
The meteorite was called ALH84001. It had been sitting in a collection in Antarctica for years, a chunk of Mars that had been blasted off the surface by an ancient impact and eventually fallen to Earth. When scientists looked closely at the rock, they found several things that, taken together, seemed to point to biology: unusual carbonate minerals, organic compounds, and — most controversially — tiny structures that looked, under an electron microscope, like fossilized bacteria.
The announcement made the front page of every newspaper on Earth. President Clinton made a statement. NASA held a press conference. For a few weeks, it felt like the question had been answered.
It hadn’t. Over the following years, researchers showed that each piece of evidence could be explained by chemistry rather than biology. The carbonate minerals could form abiotically at high temperatures. The organic compounds were likely contamination from Earth. The tiny structures were almost certainly mineral artifacts — features that form naturally in rock and happen to resemble cells at nanometer scales.
ALH84001 is the most famous example of the problem, but it is not an isolated one. Minerals routinely produce structures, patterns, and chemical signatures that look biological and aren’t. Dendrites — the branching crystal formations you sometimes see in rock — look uncannily like fossil plants or coral. Certain iron oxide minerals form rounded, layered structures called spherulites that resemble microbial colonies. Silica deposits around hydrothermal vents create stalks and filaments that, without careful analysis, are indistinguishable from fossilized microbes. In the early Earth rock record, distinguishing genuine biosignatures from mineral mimics is one of the hardest problems in geology. On Mars, where we cannot bring the rocks back to a full laboratory for analysis, it may be the hardest problem we face.
Here is the duality, stated plainly: minerals preserve the evidence of life, and minerals produce false evidence of life. The same medium that holds the answer also generates the noise. Every signal we’re looking for on Mars will be embedded in — and potentially mimicked by — the mineral matrix that surrounds it.
This is not an argument against looking. It is an argument for understanding what you’re looking at. And understanding what you’re looking at, in a mineral, requires a mineralogist.
The frameworks the astrobiology community has built for life detection — careful, rigorous, genuinely impressive work — acknowledge this problem. The best current framework, developed in part from the work done at that Caltech workshop, explicitly targets evaporitic minerals, fluid inclusions, and crystal habits as the primary sample targets for Mars life detection. Mineralogical characterization is built into the baseline measurements before any biological experiment begins.
This is not a fringe concern. Charles Cockell, one of the scientists who co-led the Caltech workshop, has argued publicly that “life” is ultimately a human definition — that the difficulty of defining it precisely is what makes finding it on other planets so hard. The problem isn’t the instruments. It’s the definition the instruments are built to detect.
But building mineralogy into the framework is not the same as having mineralogists in the room when the framework is designed. One produces a checklist. The other produces judgment.
Act 5: The Diagram
Somewhere in the first week of that Caltech workshop, while the group was working through what would become their life detection framework, I drew a diagram.
Three overlapping circles: Patterns of Chemical Structures, Morphology, and Metabolism. Each circle alone gets you to 95% confidence that you’re looking at something biological. Any two overlapping: 99.7%. All three converging on the same sample: 100%.
The probability logic was simple. What stopped a few people mid-conversation when they saw it was the phrase underneath: Depth ≈ Time.
The biologists and chemists in that room were designing experiments for a single moment — you drill, you sample, you measure. I was thinking about the vertical record. What the rock looked like at ten meters versus fifty meters versus a hundred meters. How the mineralogy would shift with depth, how the chemistry would change, what that gradient would tell you about the history of the environment. In stratigraphy, depth is not just space. It is time made physical.
But there is another timescale problem that the mineral record forces you to confront. Mars is cold. Most of the time, extraordinarily cold. Life on Earth, when it exists in cold and extreme environments, doesn’t stop — it slows down. Metabolic rates drop to near zero. Cellular processes that take minutes at room temperature can take years, decades, or centuries at Martian temperatures. A single measurement, even a sophisticated one, taken over the course of an hour or a day, may show nothing — not because there is nothing there, but because whatever is there is moving on a timescale the instrument wasn’t designed to detect. The mineral record doesn’t have this problem. A crystal that took ten thousand years to grow still holds that growth in its structure, readable long after the process ended. Biology leaves traces in minerals precisely because minerals are patient in a way that instruments are not.
The mineralogist’s question is never just is there life here. It is what has this place been through, and does the mineral record support or complicate what the biological instruments are telling us. Those are different questions. The second one requires someone trained to read rock.
I showed the diagram around. The conversation shifted.
The second week of the workshop opened with a new banner image — the official Keck promotional image for Part II of the workshop. Earth on the left. Mars on the right. And between them, bridging the two planets: photographs of mineral samples. The life detection icons traveled in both directions along that mineral bridge.
The workshop’s own banner had made the argument. I had an iPad that said the same thing in three overlapping circles and a phrase about depth.
My diagram didn’t become the final framework verbatim. But the framework that emerged — and the mission design built from it — centers evaporitic minerals, fluid inclusions, and crystal habits as the primary targets. The mineralogist’s contribution was in the architecture, not just the instrument list.
That is what it looks like when a mineralogist is in the room. Not a checklist item. A different way of reading the same evidence.
Act 6: The Specimen Drawer
Back in Los Angeles, in my office at the Natural History Museum, there is a drawer of apatite specimens that I keep coming back to.
Same mineral in every box. Same formula: Ca₅(PO₄)₃(OH,F,Cl). Same crystal system. Completely different histories.
One formed on an ancient seafloor in Germany, built up from phosphate-rich sediment over millions of years. One crystallized deep inside a cooling magma body in Brazil. One grew from hot fluids moving through fractured rock in Portugal — a collector’s holy grail. One formed where magma met limestone in Quebec, the chemistry of both transforming into something neither would have produced alone. One grew alongside emeralds in the Andes. One is a geological hybrid from Utah, carrying two different formation stories in a single crystal.
And then there is the one from Durango, Mexico. Arguably the most famous apatite in the world — not because it is the rarest or the most beautiful, but because it is the most chemically consistent. Laboratories on every continent use Durango apatite as the global calibration standard for dating rocks. When scientists need to verify that their instruments are reading correctly, they run Durango apatite first. It is the zero point. The reference against which everything else is measured.
Every one of these formed through a different process, in a different environment. Every one of them is the same mineral. And every one of them is a record — of the conditions that made it, the fluids it grew from, the geological events it survived.
That is what minerals do. They remember.
Now consider what a life detection instrument would see if it analyzed these specimens without knowing where they came from. The German specimen has rounded, layered growth that looks almost biological — the kind of morphology that would stop a Mars instrument in its tracks. Several of the others carry trace element chemistries that overlap with biologically influenced mineralization. Some formed in exactly the kinds of iron-rich hydrothermal environments that Mars orbiters have flagged as biosignature targets.
None of this is evidence of life. Not one of these specimens has anything to do with biology. But a detector on Mars, encountering chemistry and morphology like this in the subsurface, would flag every one of them for follow-up. The archive and the noise look identical until someone who knows the difference is in the room.
This is not a hypothetical concern. It is the central analytical problem of the next fifty years of planetary exploration. The Durango apatite sits in my drawer as a calibration standard — the reference point scientists trust before they trust anything else. What we need for life detection on Mars is something equivalent. Not just better instruments. A better understanding of what the mineral record can and cannot tell us, built by people who have spent their careers learning to read it.
The crystals hold the answer and the noise. Learning to tell the difference — that’s the work.
But here is the question I keep coming back to — the one I’ll be sitting with on that panel stage in a few weeks. We set out to find life on Mars. We built the instruments, designed the experiments, and sent them across the solar system. And what the search has given back so far isn’t an answer. It’s a mirror. Every framework we’ve built to detect life elsewhere has forced us to confront how poorly we understand life here. What do we actually mean by it? Where does it begin? How do we recognize it when it doesn’t look like us?
My co-panelist has spent her career reconstructing ancient genes — reading the evolutionary record backward to understand what life looked like at its earliest moments on Earth. I’ve spent mine reading minerals — the physical archive that recorded those same moments from the other side of the biology. Two different archives. The same question. What does the search for life beyond Earth reveal about life here at home?
I don’t think that question has a clean answer yet. But I think we’re finally asking it in the right room.
References & Further Reading
The KISS Workshop and REVEAL Mission Perl, S.M., Cockell, C.S., Fischer, W.W., and colleagues. “Biological Validation and Agnostic Experiments for Extinct and Extant Microbial Life within the Martian Subsurface.” Astrobiology, Viking Special Issue (in revision, 2026). [Aaron Celestian is a co-author.]
Perl, S.M., Cockell, C.S., Fischer, W.W., and colleagues. “The Biology of Biosignature Detection: Rationale and Experimental Frameworks for Biological Validation.” Report prepared for the W.M. Keck Institute for Space Studies, California Institute of Technology, 2024. DOI: 10.26206/57j7-pk96 [Aaron Celestian is a co-author.]
The Ladder of Life Detection Neveu, M., Hays, L.E., Voytek, M.A., New, M.H., and Schulte, M.D. “The Ladder of Life Detection.” Astrobiology18(11), 1375–1402, 2018.
Mineral Evolution Hazen, R.M., and colleagues. Mineral evolution framework — the progression from ~60 minerals at Earth’s formation to 5,900+ today, driven in large part by biological processes. See Hazen et al., American Mineralogist, ongoing series.
ALH84001 and the Life on Mars Debate McKay, D.S., Gibson, E.K., Thomas-Keprta, K.L., and colleagues. “Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001.” Science 273(5277), 924–930, 1996.
What is Life? (Video) Cockell, C.S. “Are Viruses Alive?” Astrobiology lecture series, University of Edinburgh, 2020.
Viking Missions Klein, H.P. “The Viking Biological Experiments on Mars.” Icarus 34(3), 666–674, 1978.
Biosignature Preservation in Evaporites Perl, S.M., Celestian, A.J., Seuylemezian, A., Tasoff, P., Baxter, B.K., Vaishampayan, P.A., and Corsetti, F.A. “Evaporitic Preservation of Modern Carotenoid Biomarkers and Halophilic Life in Martian Analogue Hypersaline Environments.” Astrobiology, 2025. https://doi.org/10.1177/15311074251392173
Another great one, thank you! Given my history analyzing kidney stones (and their apatite), you had me at the 6 different apatites :)
Go, Team Mineralogy!
And, you approached the absurd issue of Human centered definitions of “Life”.
Given that we are Human, yes, it makes sense, in a very limited, self referencing sort of way.
But couldn't we at least acknowledge that all life forms may not be apparent to our form of life?
That we have not outgrown our species centric version of defining & cataloging
things in relationship to what we think we know and assume to be true?
But Team Mineralogy demanded that an additional perspective be added to the Crazysoup of Lets go to Mars!
Depth = Time
Thank you. It’s a start.