The question is not whether intelligent life exists somewhere in the universe. The question is whether it existed here, in this solar system, before us.
Jason Wright, professor of astrophysics and astronomy at Pennsylvania State University, published a paper on arXiv in April 2017 titled Prior Indigenous Technological Species that formalized this question as a legitimate scientific inquiry for the first time in the peer-reviewed literature. Wright’s argument was specific and physically grounded: given what we know about the history of Mars, Venus, and Earth, the possibility that one or more of these bodies hosted a technological civilization before the development of modern humans cannot be ruled out by the available evidence, and the specific question of how to search for the surviving traces of such civilizations deserves systematic scientific attention.
The paper’s institutional significance is the same as the significance of any credentialed scientist publishing a serious treatment of a question that the field has previously treated as outside the bounds of legitimate inquiry. Wright is not a fringe researcher. He is a faculty member at a major research university whose publication record includes peer-reviewed work on stellar astrophysics and the search for technosignatures. His decision to publish this specific paper represents a formal scientific engagement with the prior civilization hypothesis rather than its dismissal.
The core physical argument is this: if an intelligent civilization existed on Mars approximately 500 million years ago, when Mars still had liquid water on its surface, the surface evidence of that civilization would be completely gone. Mars has no plate tectonics to subduct and recycle surface material, but it does have four billion years of meteor bombardment, wind erosion, and dust deposition that would have completely obliterated any surface structures. The subsurface, however, is protected from these erosional processes. A structure buried ten meters below the Martian surface 500 million years ago might still be there.
Whether it is there is an empirical question. Whether we have looked for it is a different question with a specific answer: we have not, because the paradigm governing solar system exploration has not included it as a research objective.
The Three Candidate Worlds
Wright’s framework identifies three candidate locations for prior indigenous technological species: Mars, Venus, and Earth itself.
Mars is the strongest candidate in terms of preserved evidence potential. The Martian surface preserves geological features dated to the Noachian period, approximately 4.1 to 3.7 billion years ago, when liquid water flowed across the surface in documented river systems and lake beds. The planet’s transition to its current cold, dry state is documented in the geological and mineralogical record of its surface. The window of habitability, broadly defined as the period when liquid water existed on the surface, spans at least several hundred million years in the early Martian history and potentially longer in isolated subsurface environments.
Whether Mars’s habitability window was sufficient for the development of complex life, let alone technological civilization, depends on assumptions about the pace of biological and civilizational development that the single terrestrial example does not allow to generalize with confidence. On Earth, complex multicellular life required approximately 3.5 billion years to develop from the earliest microbial ancestors. Whether Mars’s shorter and less hospitable habitable period could have supported equivalent development is a question the data does not answer.
The subsurface preservation argument is the specific physical basis for searching Mars rather than merely accepting the absence of surface evidence as conclusive. Mars has no plate tectonics. Its surface has been geologically stable, with localized volcanic and seismic activity, but without the crustal recycling that destroys and renews Earth’s surface on hundred-million-year timescales. A subsurface structure on Mars, protected from meteor bombardment and atmospheric erosion, could survive for geological timescales in identifiable form.
Wright’s specific suggestion is that georadar surveys of the Martian subsurface, whose technology has been deployed by the SHARAD instrument on the Mars Reconnaissance Orbiter and the MARSIS instrument on Mars Express, could be targeted to search for subsurface anomalies whose geometry is inconsistent with natural geological processes. The instruments exist. The data they produce covers significant portions of the Martian subsurface. Whether any of the anomalies in that data have been examined with prior civilization detection as an explicit research objective is not established in the available literature.
Venus presents a different case. The planet had liquid water on its surface for a documented period of approximately 2 billion years, ending when the runaway greenhouse effect began approximately 750 million years ago. Two billion years is substantially longer than the period required for complex life to develop on Earth. Whether the Venusian surface environment during its habitable period was conducive to the development of technological civilization is unknown, but the duration alone makes Venus a stronger candidate than a shorter habitable period would suggest.
The specific evidence preservation problem on Venus is the inverse of Mars: Venus’s surface is geologically young, approximately 300-500 million years in its current form, implying a catastrophic resurfacing event that would have destroyed any surface structures from the earlier habitable period. The subsurface preservation argument applies to Venus as well, but the specific geological dynamics of Venus’s catastrophic resurfacing make the subsurface preservation case more complicated than for Mars.
Earth itself is the most provocative candidate in Wright’s framework because it is the one that the available archaeological methodology is most capable of investigating. Wright notes that plate tectonics, sediment deposition, erosion, and biological processes would have eliminated virtually all surface evidence of a technological civilization more than a few million years old. The fossil record routinely documents organisms from hundreds of millions of years ago, but the physical artifacts of a technological civilization, structures, tools, refined metals, manufactured materials, are made of substances that the geological record does not typically preserve at those timescales.
The Silurian Hypothesis
In 2018, Gavin Schmidt of NASA’s Goddard Institute for Space Studies and Adam Frank of the University of Rochester published a paper in the International Journal of Astrobiology titled The Silurian Hypothesis: Would it be possible to detect an industrial civilization in the geological record?
The paper’s title refers to the Doctor Who episode whose Silurian civilization, a reptilian people who lived on Earth before humanity, is one of the more specific popular culture explorations of the prior civilization concept. Schmidt and Frank’s engagement with this reference in a peer-reviewed journal title represents an unusual moment of popular culture acknowledgment in academic science, and signals the paper’s explicit engagement with the question that Wright’s arXiv paper raised.
Their specific analysis examined what signatures an industrial civilization comparable to modern humanity would leave in Earth’s geological record if it had existed 50 million years ago. The findings are the most specific physical analysis of the evidence preservation question available in the peer-reviewed literature.
The expected geological signatures include: anomalous concentrations of specific metals including lead, cadmium, and other heavy metals associated with industrial smelting and processing, distributed globally through atmospheric deposition; elevated concentrations of specific organic compounds associated with petroleum combustion and plastics manufacturing; isotopic anomalies in carbon and nitrogen consistent with industrial agriculture’s disruption of natural nitrogen cycling; and a sharp transition in ocean chemistry associated with the acidification that accompanies atmospheric CO2 elevation.
Schmidt and Frank’s conclusion was specific and sobering: if an industrial civilization existed on Earth 50 million years ago and operated at approximately the scale of modern human civilization, the geological record might contain subtle anomalies consistent with industrial activity, but these anomalies would be extremely difficult to distinguish from natural geological variation without specific targeted investigation. A civilization that existed for a shorter period, or operated at a smaller scale, might leave no detectable trace whatsoever.
Whether the current geological record contains any such anomalies from periods predating the documented evolution of modern humans is a question that Schmidt and Frank explicitly raise and leave open for future research. The absence of obvious signatures does not rule out prior civilization. It rules out prior civilization that operated at very large scale for very long periods. Everything smaller or briefer is below the detection threshold.
What Is Already in the Ground
The specific question of whether Earth’s subsurface contains evidence of prior technological civilization connects directly to multiple existing pieces in this library’s Lost Civilizations cluster.
The documented underwater archaeology of Dwarka and the Gulf of Cambay establishes that human civilization was operating at a level of organized complexity sufficient to build harbor cities approximately 7,500-9,500 years ago in locations that are now underwater due to post-glacial sea level rise. The conventional archaeological timeline places the earliest known civilizations at approximately 5,000-6,000 years ago. The Dwarka findings represent a 3,500-4,500 year extension of that timeline in a single documented location.
If the conventional timeline is already being extended by thousands of years through underwater archaeology, the question of how far back organized complexity extends is genuinely open. The Gobekli Tepe complex in Turkey, documented in the excavation record and dated to approximately 11,500 years ago, represents intentional large-scale architecture whose sophistication exceeds what the conventional model expected for that period.
Wright’s framework does not require the prior civilization to be a previous human civilization. It requires only that the evidence of their presence be distinguishable from natural geological processes if specifically searched for. The distinction between a previous human civilization with advanced technology, an entirely different intelligent species that occupied an earlier Earth, and a genuinely extraterrestrial presence operating on Mars or Venus before humanity evolved, is a distinction that the evidence base would need to be much more developed to make.
What the Wright and Schmidt-Frank papers establish is that the question deserves to be asked with specific physical methodology rather than dismissed as inherently speculative. Both papers are in the peer-reviewed literature. Both are authored by credentialed researchers at major institutions. Both propose specific detection methodologies whose application to the available data could produce falsifiable results.
The question has been formalized. The methodology has been proposed. The search has not been conducted.
The Technosignature Research Program
Wright’s broader research program, which extends beyond the prior civilization paper into the systematic study of technosignatures across the galaxy, is documented in multiple subsequent publications and in his role in the development of the technosignature research field within the SETI community.
The term technosignature, popularized in the SETI literature partly through Wright’s work, describes any physically detectable signature of technological activity, including Dyson sphere infrared waste heat documented in the Two Galaxies Producing Unexplained Infrared Radiation piece in this library, atmospheric biosignatures from industrial activity, laser communication signals, and the specific subsurface structural anomalies that Wright’s prior civilization paper focuses on.
The 2018 NASA technosignature workshop, which Wright participated in and whose proceedings are documented in the NASA technical report literature, represented the first formal NASA institutional engagement with the technosignature search concept since the cancellation of NASA’s SETI program in 1993. The workshop’s proceedings, published as a formal NASA report, established that technosignature research is a legitimate component of the astrobiology research program and that NASA resources could appropriately be applied to it.
Whether NASA has subsequently applied specific resources to subsurface technosignature searches on Mars or the Moon is not established in the available public record. The instruments capable of conducting such a search, georadar systems on Mars orbiters, exist and are operational. The research objective of searching for prior civilization evidence has been proposed in the peer-reviewed literature by a named researcher at a major institution.
The gap between the proposal and the search is the specific institutional fact that Wright’s paper makes most visible: the question has been asked formally. The answer has not been looked for formally.
What the Framework Establishes
Wright’s Prior Indigenous Technological Species paper establishes the following without requiring any specific prior civilization to have existed: the physics of geological preservation on Mars and the Moon are consistent with the survival of subsurface technological structures over hundreds of millions of years; the detection methodology for such structures, georadar and other subsurface imaging techniques, exists and is deployed on active space missions; and the prior civilization hypothesis is not ruled out by any currently available evidence.
The Schmidt-Frank Silurian Hypothesis paper establishes that an industrial civilization on Earth within the past 50-100 million years would likely not leave obvious surface traces detectable in the current geological record, and that the absence of obvious traces cannot be interpreted as absence of prior civilization.
Whether prior technological civilizations existed in this solar system before humanity is a question that the peer-reviewed literature has now formally placed in the domain of falsifiable scientific inquiry rather than in the domain of speculation.
The instruments are on Mars. The data they produce is in the archive. The research objective has been proposed in print by a Penn State astrophysics professor.
Whatever is in the Martian subsurface has not been specifically searched for with prior civilization detection as the stated objective.
Whether that search would find something, or would find nothing and establish the absence more rigorously than the current default assumption does, is the question that Wright’s paper placed in the research agenda in 2017.
It has not been answered.
