Biosignature Standards

Established Every claimed detection of life beyond Earth has failed, and the failures have a structure worth learning. Four of them are well documented: a Martian meteorite whose four independent lines of evidence each acquired an abiotic explanation; a Viking experiment whose positive result was undermined by a companion instrument and later by perchlorate chemistry; a phosphine line in Venus’s clouds that dissolved into a baseline-fitting artefact; and a sulfur-bearing molecule in an exoplanet atmosphere whose significance fell apart under independent reduction. No two failed at the same point. That is the argument for having a scale rather than a threshold.

Established The community has a scale and has not adopted it as a rule. The confidence-of-life-detection framework proposed in 2021 defines seven ascending levels: a signal known to be produced by life; contamination excluded; a biologically plausible context; known abiotic sources excluded; independent detection of the same signal; corroborating independent signals; and independent verification by another team on another sample or target. It is a good instrument. It has been cited approvingly by agencies, used rhetorically in press conferences, and required by no journal, no funder and no mission.

Frontier The false-negative side is as important and gets almost no attention. Present instruments cannot detect an Earth-like atmosphere on an Earth-like planet around a Sun-like star at any confidence, and the best rocky targets available are around M dwarfs where thermal emission measurements have so far been consistent with bare rock. A field that cannot detect the positive case must be extremely careful about what it concludes from nulls, and it usually is not.

Frontier This brief joins five literatures that rarely cite each other: remote spectroscopy and its abiotic false positives; in-situ chemistry and its contamination problem; the sample chain from target body to laboratory; the prior-probability structure that decides what a three-sigma feature is worth; and the technosignature community’s parallel framework for grading claims. The unifying claim is that biosignature validation is a problem in evidential standards rather than detection physics, and the standards are under-specified at every level below the top one.

Established A note on sourcing. This brief was commissioned in September 2026 from the Institute’s research base. Reading-list entries without links are cited from the bibliographic record rather than re-fetched, and claims are dated no later than early 2026 unless carried by a linked source.

Established The Martian meteorite case defined the modern standard by failing in public. The 1996 claim for relic biogenic activity in ALH84001 rested on four things found together: polycyclic aromatic hydrocarbons, magnetite crystals resembling those made by magnetotactic bacteria, carbonate globules, and sub-micrometre structures interpreted as fossils. Each acquired a credible abiotic account over the following decade: terrestrial contamination for some organics, thermal decomposition of carbonate for the magnetite, and structures smaller than any known cell and consistent with mineral artefacts. The magnetite argument survived longest and is no longer consensus. The episode is why co-occurring suggestive signals are now treated as weak evidence when each has its own abiotic route.

Frontier Viking is the one case where the disagreement never resolved. The Labeled Release experiment produced a response consistent with metabolism, including the expected loss after heat treatment; the companion gas chromatograph mass spectrometer found no organics at its detection limit. Perchlorates found in Martian soil three decades later supplied a mechanism for both: perchlorate combusts organics during pyrolysis, and perchlorate chemistry can generate oxidants that mimic a metabolic signal. Both readings survive. What killed the biological interpretation was not disproof but the absence of any path to levels five through seven — the experiment has never been repeated on Mars.

Established Venus is the cleanest demonstration that claims fail low on the scale, not high. The 2020 report of about 20 parts per billion of phosphine in the Venusian cloud deck was argued as a biosignature because no known abiotic route produces phosphine in an oxidised atmosphere at that abundance. Within a year, independent reanalysis showed the spectral line depended on a high-order polynomial baseline fit to the interferometric data, that a sulfur dioxide transition sits close to the phosphine frequency at the relevant resolution, and that a calibration problem in the observatory’s own processing had affected the dataset. Later observations by other instruments did not recover the feature at the original abundance. The claim failed at level two — instrumental and reduction artefacts — before the interesting argument about abiotic chemistry could even be had.

Established The exoplanet case shows the same failure mode at a different level. Reported detections of dimethyl sulfide and dimethyl disulfide in the atmosphere of the sub-Neptune K2-18 b, at roughly three sigma, were argued as a biosignature because on Earth those molecules are made almost exclusively by marine life. Independent groups reanalysing the same data reached lower significances or none: one found no statistically preferred mid-infrared feature at all, another concluded the evidence is insufficient once a wider set of chemical models and reduction choices is admitted. The disagreement is not about whether the molecules would be biological if present, but about whether a three-sigma feature survives a different pipeline. Often it does not.

Established Three sigma is not a detection threshold in a search with this many trials. Thousands of planets, dozens of candidate molecules, several reduction pipelines and a strong publication incentive guarantee a steady supply of three-sigma features. Particle physics adopted a five-sigma convention for exactly this reason after a history of three-sigma claims evaporating. Exoplanet spectroscopy has no equivalent convention and does not generally pre-register analysis choices.

Established The false-negative floor is measured and it is high. Thermal emission from the innermost TRAPPIST-1 planet matched a bare-rock prediction to within a few kelvin, effectively excluding a thick atmosphere; the next planet out was shown to lack a thick carbon dioxide atmosphere; and deep observations of the habitable-zone planet in the same system have so far constrained rather than detected a secondary atmosphere. These are the most favourable rocky targets in the sky for the most capable telescope ever flown. The inference is not that those planets are dead; it is that the instrument reaches an Earth-like atmosphere on an M-dwarf planet only marginally, and does not reach one around a Sun-like star at all. Exoplanet Colonization lands the same point from the habitability side: six thousand confirmed planets and zero confirmed rocky-planet atmospheres.

Established Oxygen, the canonical biosignature, has well-characterised abiotic routes. Photolysis of carbon dioxide with inefficient recombination, and runaway ocean loss on planets around active M dwarfs followed by hydrogen escape, can both build oxygen-rich atmospheres with no biology. The response has been to specify context rather than molecules: oxygen with methane, oxygen without carbon monoxide, the absence of the collision-induced absorption feature that betrays a very massive abiotic oxygen atmosphere. This is the right move and it raises the observational bar substantially, because a context requirement means detecting several species at once in the same marginal spectrum.

Frontier The in-situ record on Mars is a contamination-controlled chain and it is working. Curiosity’s onboard laboratory has detected chlorinated hydrocarbons and a range of aromatic and aliphatic organics preserved in ancient mudstone, in contexts that argue for indigenous origin. Perseverance has identified organic-consistent signatures and, at one sedimentary target, mineral reaction fronts described as a potential biosignature requiring laboratory confirmation. These are level-three and level-four results, correctly reported as such, and nothing in the rover’s payload can take them further — which is the whole argument for sample return.

Established The technosignature community grades claims better than the biosignature community does. Infrared-excess candidates proposed as partial Dyson spheres were tested by follow-up radio imaging showing the excess in at least one case is consistent with a blended background galaxy, and the candidate list was cut by an independent team using an independent method and published as such. A candidate narrowband signal from the direction of Proxima Centauri was traced to terrestrial interference by the team that found it. A merit-axis framework for technosignature searches predates the biosignature scale and is more used within its field. The difference is cultural, not technical.

Frontier Agnostic biosignatures are the most promising and least mature category. Rather than molecules life makes here, they look for properties any chemistry-based life should produce: enantiomeric excess in chiral molecules, molecular complexity above an abiotic ceiling, isotopic fractionation, or atmospheric thermodynamic disequilibrium. Complexity-based mass-spectrometry approaches propose a measurable threshold, and the theoretical framework behind them has drawn serious criticism. Chirality remains the strongest candidate: meteoritic amino acids are broadly racemic with small and debated excesses in a few species, so a large excess in a Martian or ocean-world sample would be hard to explain abiotically.

Frontier What is the abiotic baseline for the specific molecules being claimed? For dimethyl sulfide the honest answer is that it is poorly constrained: photochemical production routes in hydrogen-rich atmospheres have been proposed, laboratory yields are sparse, and cometary detections of the molecule exist. A biosignature argument of the form “on Earth only life makes this” is an argument about Earth’s chemistry, not about chemistry.

Frontier How much of a marginal spectral feature is reduction choice? The K2-18 b episode suggests a lot. Detrending, systematics models, limb-darkening treatment and the choice of retrieval grid each move significance by amounts comparable to the claimed signal. Nobody has quantified this across pipelines on a common dataset with a pre-agreed protocol, which is why the disagreements are resolved by argument rather than by measurement.

Frontier What is the prior, and can it be anything but a choice? Converting a signal into a probability of life requires a prior that nothing constrains. Occurrence-rate work bounds how many rocky habitable-zone planets exist per star — Kepler-based estimates cluster in the tens of per cent with error bars spanning nearly an order of magnitude — but that is the number of places, not the probability of occupancy. Analyses reporting a posterior probability of life are reporting their prior with extra steps.

Speculative Would we recognise a biology unlike ours? Every biosignature in use is calibrated on terrestrial biochemistry. A biology with different polymers, a different solvent or inverted chirality would produce different signatures and might register as anomalous abiotic chemistry. Xenobiology is the closest thing to a laboratory for this question, because it builds organisms with orthogonal chemistries and can ask what they leave behind.

Frontier Can a positive result ever be verified independently in the strict sense? Level seven requires another team, another instrument, another sample. For a returned Mars sample this is achievable by splitting the sample. For an exoplanet it requires a second telescope of comparable capability observing the same target, which for the flagship candidates does not exist and is not funded. A framework whose top level is unreachable for most targets needs an explicit statement of what the achievable ceiling is.

Established The photon budget is the hard limit on remote detection. Transit spectroscopy of a rocky planet delivers tens of parts per million against stellar variability of comparable amplitude, requiring dozens of transits and exquisite stability. Direct imaging of an Earth analogue around a Sun-like star needs contrast near 10^-10 at small separation, which no flown coronagraph approaches. Mega-Telescopes sets out why the necessary aperture scales so badly in cost and why the instruments that could close the gap are a decade or more away.

Established Stellar contamination is a first-order systematic, not a nuisance term. Unocculted starspots and faculae imprint features on a transmission spectrum that mimic planetary absorption, and for active M dwarfs the effect can dominate. Separating stellar from planetary signals requires a stellar model of a kind that does not exist at the needed fidelity, which is why several published rocky-planet spectra are best described as measurements of the star.

Frontier In-situ instruments trade sensitivity against ambiguity. Pyrolysis-based organic analysis destroys the structures it characterises and is vulnerable to perchlorate combustion; laser desorption preserves more and has flown less; chirality-capable separation matters most for agnostic biosignatures and has never operated on Mars. Every in-situ instrument carries its own organic blank, which is why witness materials and contamination budgets are part of the evidence.

Established The sample chain is the bottleneck for the strongest candidates. The only route from a level-four in-situ result to a level-seven verified one runs through a terrestrial laboratory, which requires a return mission, a contamination-controlled chain of custody and, for restricted targets, containment. Planetary Protection documents that chain and its funding crisis; the point here is that the evidential standard and the logistics are the same problem.

Established Curation cleanliness is a precondition for any organic claim. The analysis of nitrogen-rich soluble organic matter in returned asteroid samples is defensible only because the capture, curation and handling chain was documented well enough to distinguish indigenous from terrestrial molecules. Any Martian biosignature claim inherits that requirement with a containment layer added.

Frontier Abiotic chemistry laboratories are the rate limiter on false-positive elimination. Level four asks that all known abiotic sources be excluded, which presumes a catalogue of abiotic sources. That catalogue is assembled one experiment at a time in a small number of laboratories on modest budgets, and it is systematically thinner for exotic environments — hydrogen-rich atmospheres, high-pressure supercritical fluids, radiation-processed ices — which is exactly where the interesting claims arise.

Established The statistical machinery is borrowed and incompletely adapted. Detection significance, trials factors, model comparison and nested sampling come from other fields with different data structures. The result is that the same dataset can yield different Bayes factors under different model priors with no agreed convention for reporting them, and that reported significances are rarely corrected for the number of molecules searched.

Frontier Instrument roadmaps set the ceiling on what standards can require. A framework demanding independent detection by a second comparable facility is unenforceable while only one such facility exists. What the standard can ask for is bounded by the flagship programme pipeline, which makes this partly a funding question dressed as a methodological one.

Frontier The decisive observation is whether TRAPPIST-1 e has a secondary atmosphere. It is the best-placed temperate rocky planet accessible to the most capable telescope in existence, it has been the target of a large dedicated observing programme, and the two inner planets in the same system have already returned bare-rock-consistent and thick-atmosphere-excluded results. A clear atmospheric detection would be the first for a temperate rocky exoplanet and would give the validation framework its first real object to work on, moving the whole subject from methodology to measurement. A null at the programme’s full depth would establish that the nearest and most favourable rocky planets around M dwarfs are airless, which removes the near-term target list for remote biosignature work entirely and pushes the question to a generation of telescopes that does not yet exist. Either result changes this brief’s assessment more than any other measurement now under way.

Frontier The cheapest informative experiment is a blind multi-pipeline reanalysis. Give several independent teams the same raw exoplanet dataset, a pre-registered protocol, and no knowledge of each other’s intermediate results, and publish the spread of derived significances for a fixed list of molecules. This measures directly the quantity that the K2-18 b dispute argues about, requires no new hardware, and has an established precedent in the many-analysts studies run in other empirical fields. Nobody has organised one.

Frontier The only candidate that could reach the top of the scale this century is in a tube on Mars. Perseverance’s cached samples, including the sedimentary target whose mineral reaction fronts have been described as a potential biosignature, can be split among laboratories and analysed by independent teams with independent instruments — the only configuration in which levels five, six and seven are simultaneously achievable. That path runs entirely through the sample-return programme described in Planetary Protection, and shares its funding risk.

Frontier Venus has a decisive in-situ measurement with a mission attached. A descent probe carrying a mass spectrometer through the cloud deck would settle the phosphine question directly, at abundances and with a specificity that ground-based millimetre spectroscopy cannot reach, and would also measure the noble-gas and isotopic context that any interpretation requires. This is the rare case where the decisive measurement is straightforward, the instrument class is mature, and the only variable is whether the mission flies on schedule.

Established The instruments that would settle the remote question are specified and unbuilt. Oxygen on an Earth analogue around a Sun-like star requires a space telescope suppressing starlight to near 10^-10 contrast, stable over hours, at a few tens of milliarcseconds. Ground-based extremely large telescopes with high-resolution spectrographs offer a partly independent route, cross-correlating many molecular lines against a template. Both are in development; neither has returned a rocky-planet atmosphere.

Frontier In-situ engineering should prioritise chirality and structure over sensitivity. The measurement with the best ratio of diagnostic power to ambiguity is enantiomeric excess in amino acids or sugars, which requires chiral separation and a non-destructive ionisation path. That instrument class is mature in terrestrial laboratories and has not flown to a target of interest. Adding a decade of sensitivity to a pyrolysis instrument buys less than flying a chirality measurement once.

Established Contamination control is an engineering requirement with a numeric specification. Sample tubes cleaned and characterised to organic-contamination levels below anything previously flown, sealed before launch, with witness materials opened at defined points, are what make a returned Martian organic measurement interpretable. This is the same discipline that asteroid-return curation demonstrated, applied prospectively rather than retrospectively.

Frontier Data infrastructure is an underrated part of the standard. Independent reanalysis requires raw data, calibration products and reduction code released together, promptly, in a form another team can run. The disputes in section 2 were resolvable only because the observations were archived, and took years longer than necessary because the pipelines were not.

Established The observational capability sits in the telescope brief. Mega-Telescopes establishes the cost scaling that determines when an instrument capable of the Earth-analogue measurement exists, and the funding record that makes its schedule uncertain. Any biosignature standard that requires independent confirmation by a second facility is writing a cheque against that programme.

Established The target inventory and its emptiness are covered next door. Exoplanet Colonization carries the confirmed-planet counts, the conservative habitable-zone sample, and the measured atmospheric nulls on the TRAPPIST-1 planets, which are the same data this brief reads as a false-negative floor.

Established The chemistry of unfamiliar life and the logistics of getting samples are the two flanking disciplines. Xenobiology is where alternative biochemistries are actually built and where the question of what a non-terrestrial biology leaves behind can be studied experimentally. Planetary Protection owns the contamination control, the sample chain and the containment architecture on which the strongest candidate evidence depends.

Established The technosignature literature is the methodological sibling. Interstellar Archaeology covers the search for artefacts and engineering signatures, including the merit-axis framework and the candidate-elimination record this brief holds up as the better practice. Directed Panspermia is the reason one specific false positive — terrestrial life found somewhere it was deliberately sent — is not purely hypothetical.

Established No body has authority to certify a detection, and none is proposed. There is no equivalent of a review panel that declares a discovery, as particle physics has through collaboration-internal thresholds and as gravitational-wave astronomy has through a formal alert and publication pipeline. Announcements are made by author teams and press offices; the correction arrives months later in a separate paper with a fraction of the readership. That asymmetry is the most damaging institutional feature of the field.

Frontier The scale exists; the editorial hook does not. A journal could require that any paper claiming a biosignature state its level on the published framework and justify it, exactly as clinical journals require trial registration. No journal does. A funder could require pre-registration of reduction and retrieval choices for observations proposed as biosignature searches. None does. These are cheap interventions with clear precedent in other fields, and their absence is a choice.

Established Press practice is part of the evidential system whether anyone likes it or not. The 1996 meteorite claim was announced with a presidential statement, and the phosphine and dimethyl sulfide results were briefed with language that outran the statistics. Agencies have since adopted more careful language; the incentive is unchanged, because attention is allocated to the announcement and not to the reanalysis.

Frontier The post-detection question is unowned. Post-detection protocols exist as voluntary declarations in the technosignature community and essentially nowhere for biosignatures. Who confirms, who announces, who holds the data, what a government does with a level-six result on a solar-system target — none of it has an owner, and a positive result inside a containment facility is simultaneously a scientific finding and a biosafety event.

Speculative The institution worth building is boring and specific. A standing, independently funded reanalysis team whose job is to re-reduce every published biosignature claim under an agreed protocol and publish the result regardless of direction would do more for the field’s reliability than any instrument now planned. Nobody funds negative results, which is why it does not exist.

Established Overclaiming has a measurable cost and the field has paid it repeatedly. Each deflated claim spends credibility the next one needs, and the pattern is legible from outside: a striking announcement, a wave of coverage, a quieter correction. The cost falls on the discipline and the benefit on individual teams, which is the structure institutional rules exist to fix.

Frontier The precautionary asymmetry runs the opposite way from most fields. A false positive is embarrassing and self-correcting. A false negative on a solar-system target can be irreversible, because a site declared lifeless may then be contaminated, drilled or settled. That asymmetry argues for a lower threshold for protective action than for announcement, and the two thresholds are routinely conflated.

Speculative A confirmed detection is a governance event, not only a scientific one. If life is found in the solar system, what follows — whether to sample further, whether to sterilise, whether settlement proceeds, who decides — is political and unassigned. Terraforming is the limiting case: an irreversible decision presupposing an answer the evidential standards cannot yet give.

Frontier This is the highest-stakes measurement problem a civilisation currently has the instruments to attempt. Whether life arose more than once determines the interpretation of every other astrobiological number, and the answer is reachable with hardware that either exists or is in development. That makes the evidential standards load-bearing rather than academic: the result will be believed or disbelieved on the strength of a framework the field has not yet committed to.

Speculative The likeliest real outcome of the next twenty years is ambiguity, and nobody is planning for it. The most probable state in 2045 is not a confirmed detection or a clean null but two or three level-four candidates that cannot be pushed higher with available instruments, and a field whose rhetoric is built around a binary announcement has no way of living with a stable, honest maybe.

Handwave The claim that detection would transform human self-understanding is asserted more often than examined. The historical analogues — heliocentrism, deep time, common descent — each took generations to propagate and were contested throughout. A microbial detection on Mars announced at level six would more plausibly produce a decade of argument about contamination than an immediate change in anyone’s worldview, and treating the transformation as automatic is where the argument works by assertion.

These horizons track when the validation framework acquires force, when the instruments reach the measurement, and when a claim could plausibly reach the top of the scale.

• 10 yr: Frontier The TRAPPIST-1 atmospheric question resolves one way or the other; extremely large ground telescopes begin high-resolution cross-correlation work on nearby rocky planets; a Venus descent mission either flies and settles the phosphine question or slips again. Expect at least two more three-sigma biosignature claims and at least two more deflating reanalyses. A journal or funder adopting the confidence scale as a requirement is plausible and not yet in evidence.
• 25 yr: Speculative A flagship direct-imaging observatory, if funded on the current roadmap, reaches oxygen and methane on a handful of nearby Earth analogues. Returned Martian samples, if the programme survives, are analysed by independent teams — the first time any candidate biosignature has had access to levels five through seven. The most likely outcome across both is several level-four candidates and no consensus detection.
• 50 yr: Speculative A statistical answer becomes possible: with dozens of characterised terrestrial atmospheres, the question shifts from adjudicating individual claims to measuring how often the relevant signatures occur, which is a much more robust form of evidence than any single detection. Ocean-world in-situ missions, if flown, supply the other independent line.
• 100 / 250+ yr: Handwave Projections here depend on propulsion and instrument capabilities nobody can bound. An in-situ measurement at another star is the only thing that would close the question definitively, and nothing in the current evidence base says whether that is a two-century problem or a permanent one.

• Depends on the aperture and contrast economics set out in Mega-Telescopes, which bound what any remote standard can demand; the target inventory and measured atmospheric nulls in Exoplanet Colonization; the sample chain and containment architecture in Planetary Protection, without which no in-situ candidate can be promoted; and the alternative-biochemistry work in Xenobiology, which is the only experimental handle on whether our signature list is parochial.
• Requires (not on this map) a systematic laboratory catalogue of abiotic production routes for every gas anyone proposes as a biosignature, since level four presumes such a catalogue exists; a measured abiotic production rate for dimethyl sulfide in hydrogen-rich atmospheres specifically, which is the molecule the current dispute turns on; a pre-registration norm for reduction and retrieval choices in observations proposed as biosignature searches; a journal or funder requirement that claims state and justify their level on the published confidence scale, which is the cheapest available intervention and has no adopter; a space coronagraph holding contrast near 10^-10 at small separations, which no flown instrument approaches; and a chirality-capable separation instrument actually flown to Mars or an ocean world, the single highest-value in-situ measurement never attempted.
• Enables a defensible answer to whether life arose independently more than once, and therefore the empirical content of every occurrence-rate argument downstream of it, including those in Directed Panspermia and Interstellar Civilization Models. It also supplies the evidential standard a settlement or terraforming decision would have to clear before declaring a world lifeless.
• Adjacent to Interstellar Archaeology, whose merit-axis framework and candidate-elimination record this brief treats as better practice; Multi-Messenger Astronomy, whose alert-and-confirmation pipeline is the nearest working model of an institutional detection standard; and Terraforming, the decision that presupposes the answer.

Established “Scientists have found signs of life on K2-18 b.” What was reported was a roughly three-sigma spectral feature attributed to dimethyl sulfide and dimethyl disulfide, in a planet whose bulk composition and interior structure are themselves contested. Independent reanalyses of the same data found the feature not statistically preferred, or the evidence insufficient once a wider range of chemical models and reduction choices is admitted. The correct description is a contested marginal feature at level one or two on a seven-level scale.

Established “Phosphine was detected on Venus and then covered up.” There was no suppression; there was a reanalysis. The original line depended on a high-order polynomial fit to interferometric data, a nearby sulfur dioxide transition complicates the identification, and a processing error in the observatory pipeline affected the dataset. Subsequent programmes report tentative low-abundance recoveries that remain disputed. The subject is open as an instrumental question, and reading a normal and rather fast self-correction as a conspiracy gets the sociology exactly backwards.

Handwave “Multiple independent lines of evidence make a claim strong.” Only if the lines are actually independent and each is individually improbable under abiotic chemistry. The Martian meteorite case had four lines that were not independent — they shared a sample, a set of preparation steps and an interpretive framework — and each acquired its own abiotic account. Counting lines is not a substitute for eliminating abiotic sources for each one.

Frontier “Oxygen in an exoplanet atmosphere would settle it.” It would not, on its own. Carbon dioxide photolysis with slow recombination, and ocean loss with hydrogen escape around active M dwarfs, both build oxygen-rich atmospheres abiotically. The discriminating observations are contextual — oxygen together with methane, the absence of carbon monoxide, the absence of the oxygen-dimer feature that signals a massive abiotic atmosphere — and every one of them is harder to obtain than the oxygen detection itself.

Speculative “Anomalous interstellar objects are candidate artefacts until shown otherwise.” This inverts the burden. For the recent interstellar comet, the reported anomalies have conventional cometary explanations, and direct infrared spectroscopy characterised its outgassing as a natural volatile-rich body. Treating unexplained as artificial is the failure mode the technosignature community wrote its merit framework to prevent, and it is instructive that the field’s own practitioners are the loudest correctors.

Frontier “A null result means the planet is dead.” Current instruments cannot detect an Earth-like atmosphere on an Earth analogue around a Sun-like star at all, and reach one around an M dwarf only marginally. Reporting non-detections as evidence of absence without stating the detection limit as a physical quantity is the most common error in the secondary coverage, and occasionally in the primary literature.

Handwave “We will know it when we see it.” The record says otherwise: four prominent claims, four different failure points, and no case where the answer was obvious on inspection. The argument for a graded, explicit, independently checkable standard is that unaided expert judgement has already been tested on this exact problem and has not performed well.