In 1925, while exploring the remote jungles of the Amazon on a quest to uncover a fabled lost city, British explorer Percy Fawcett and his small expedition party vanished without a trace.

Fawcett, a noted geographer, artillery officer, cartographer, surveyor, and archaeologist, set off into the rainforest accompanied only by his son, Jack Fawcett, and Jack’s best friend, Raleigh Rimell. Their goal was to locate an ancient lost city rumored to exist in the heart of the Amazon that Fawcett and others called “The Lost City of Z.”

While Fawcett and his expedition crew’s fate remains unknown, new advancements in modern archaeological science, propelled by technologies that include unmanned aerial vehicles and LiDAR, are now revealing what could be the archaeological reality behind part of what the ill-fated British explorer sought.

“The reward is that we’re finally finding the ‘lost civilisation’ that explorers like Percy Fawcett were searching for a century ago,” says José Iriarte, a professor of archaeology at the University of Exeter, writing in a piece featured at The Conversation, though adding that such discoveries are now being made “by cajoling a drone rather than battering through jungle.”

LiDAR: Unearthing Lost Worlds Hidden from Time

For a time, archaeologists presumed that the Amazon rainforest was a vast wilderness that, while abundant in resources, would have been capable of supporting only small, scattered communities.

With the aid of modern technologies, those past ideas have gradually changed as new archaeological evidence continues to push researchers toward rethinking past assumptions. Among these technologies is advanced laser-mapping technology known as LiDAR (light detection and ranging), which archaeologists have put to great use in the last several decades to aid in uncovering evidence of surface features that were once either inaccessible or otherwise invisible during ground-based surveys.

Something else that LiDAR excels at is penetrating the dense forest of areas like the Amazon, enabling researchers to get unprecedented aerial views of the surface below the canopy, along with any structures that may have been left there by humans from long ago. The result has been evidence of sprawling ancient societies hidden beneath the cover of thick jungle, revealing the Amazon as a region that once supported large populations that existed in sophisticated, interconnected landscapes.

Rediscovering a ‘Lost Civilization’ in the Amazon

A particularly striking example of such discoveries involves the Llanos de Moxos region of northern Bolivia, where recent LiDAR surveys have revealed the presence of a sprawling archaeological site long hidden by dense jungle. Archaeologists believe the ancient settlement is linked to what is called the Casarabe culture, which would have thrived in the area sometime between A.D. 500 and 1400.

“The Casarabe organized into a hierarchy of four different sizes of settlements,” writes Professor Iriarte in his recent piece at The Conversation. “The biggest ones—the primary settlements—were as large as 3km² or 300 hectares.”

“That’s enough space for over 400 football pitches,” Iriarte notes, “suggesting that they could have accommodated substantial numbers of people.”

Unseen Evidence of an Ancient Amazonian Culture

Viewed from the ground, an observer who braved this dense region of Bolivian jungle might only see thick patches of forest separated by grassland savannahs.

That all changes when viewing LiDAR imagery obtained during aerial surveys, however. Through the sensitive detection capabilities afforded by laser pulses that can easily penetrate the dense vegetation, a lost world emerges—one the likes of which Percy Fawcett and other early explorers once only dreamed of rediscovering.

Researchers have now successfully identified a vast network of settlements at Llanos de Moxos, connected by raised causeways, canals, reservoirs, and engineered agricultural systems that cover an area of close to 20,000 square kilometers.

These complexes upend past thinking about the presence of isolated settlements in the region, and instead appear to show sites covering areas as large as three square kilometers, featuring monumental civic and ceremonial architecture, towering conical pyramids that ascend to heights of 20 meters, and the presence of massive U-shaped structures, which archaeologists believe had likely served as ceremonial structures that once hosted gatherings.

Unprecedented Scale of a Hidden World

Another surprising feature is the scale of the structures archaeologists have uncovered, which they say rivals some of the most well-known monuments like those of the ancient Tiwanaku civilization in the Andes.

Yet, unlike many densely packed ancient cities, the Casarabe landscape also differs in several ways: the unique variety of urbanism it reflects is suggestive of dispersed populations whose connected infrastructure also brought them together through ancient shared water management systems.

“It was clearly all planned and coordinated,” Iriarte explains, adding that the ancient builders at Llanos de Moxos engaged in precocious designs that were intended “not only as living spaces but for integrating the population across the region.” Similar architectural planning has been observed at other ancient sites around the world, which include those assembled by the ancient Maya of Central America, as well as the builders of Angkor across the world in Cambodia.

The “Dark Earth” Enigma

Beyond just architecture and clues to the way of life of these ancient societies, researchers are also gaining new insights into the agricultural practices of the early Amazonian world.

For many decades, scientists presumed that a major limiting factor on the region’s ability to sustain larger populations hinged on the presence of factors that included poor soils, seasonal flooding, droughts, and tropical diseases. However, mounting evidence suggests that the indigenous societies of the region were far from hindered by the landscape, and instead managed to transform and manage farmland at scales previously unimagined.

Along with sophisticated agricultural systems, ancient Amazonians were also capable of engineering remarkably fertile soils, known as Amazonian Dark Earths, which Iriarte says “combined charcoal, bone and waste materials with the existing poor-quality soil to make it fertile enough for widespread farming.”

“Amazonia had reclaimed vast expanses of seasonally flooded savannahs over several thousand years to create raised and drained field systems,” he adds, also noting the construction of extensive drainage networks and the cultivation of diverse crops such as maize. Rather than merely adapting to the rainforest, the ancient inhabitants of the Amazon actively reshaped it.

An Amazonian Archaeological Revolution

Thanks to similar LiDAR surveys that have recently been undertaken in nearby countries, including Ecuador’s Upano Valley, where thousands of structures linked by roads and organized according to highly structured settlement plans have been detected, the recent findings at Llanos de Moxos are one of the latest additions to a broader revolution in archaeology made possible through such exciting Amazonian discoveries.

In addition to Bolivia and Ecuador, researchers have also documented ceremonial earthworks, geometric enclosures, and sprawling ancient settlements in Colombia, Peru, and Brazil in recent years, all of which are challenging decades of past assumptions about ancient life in the Amazon.

Despite the recent advancements in our understanding, many questions remain unanswered. Among the questions archaeologists have are those related to how these ancient societies were governed, as well as what factors led to their decline, a fall which was precipitated by unknown factors that occurred before European arrival.

Possible contributing factors may include shifts in ancient climates, as well as environmental pressures. It is also possible that political changes or conflicts that emerged between neighboring societies may have played a role, which could have contributed to disruptions in trade networks that may have further weakened these once thriving societies.

Despite the remaining mysteries about these enigmatic cultures, one thing is becoming increasingly clear: the Amazon was far from being the unclaimed tropical wilderness many long believed it to be. In many ways, the fascination with lost cities and ancient civilizations that drove explorers like Percy Fawcett—and which led to his untimely fate—had more basis in reality than many historians, archaeologists, and explorers probably guessed.

As ongoing LiDAR surveys continue to expand across previously unexplored regions, archaeologists believe thousands more structures may still await discovery, suggesting that some of the Amazon’s greatest archaeological secrets remain hidden, but no longer kept entirely from view.

“What lies beneath the Amazon is not just a hidden past,” Iriarte says. “It is a reminder that even the most seemingly untouched landscapes can carry deep histories, waiting—sometimes just beneath our feet—to be revealed.”

Professor José Iriarte’s complete article appeared at The Conversation on June 8, 2026.

Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. A longtime reporter on science, defense, and technology with a focus on space and astronomy, he can be reached at micah@thedebrief.org. Follow him on X @MicahHanks, and at micahhanks.com.

A new proposed Senate bill aims to establish clear guardrails for the U.S. military’s use of artificial intelligence (AI), drawing a definitive line on one of the most consequential questions in modern warfare: who has the final say when lethal force is used?

On June 8, Senator Adam Schiff (D-Calif.) introduced the proposed Human Authority in Lethal Operations Act of 2026, or “HALO Act,” which would impose sweeping requirements on the Department of War (DoW) to ensure that autonomous and semi-autonomous weapon systems remain under meaningful human control.

The legislation would establish new design standards, testing requirements, oversight procedures, and legal safeguards for military systems that use artificial intelligence to identify, recommend, prioritize, or engage targets.

The bill aims to ensure that responsibility for battlefield decisions remains with human commanders, rather than shifting to algorithms. The legislation would require the Pentagon to designate accountable commanders for any engagement involving AI-enabled autonomous or semi-autonomous weapons and mandates that those commanders retain “ultimate discretion, judgment, and control over the use of force.”

“The past few months have shown us that there is an urgent need for commonsense guardrails to ensure the Defense Department’s use of AI is in line with Americans’ national security and privacy priorities,” Sen. Schiff said in a press release. “There are good reasons to use AI technology to advance our national security,” although he emphasized that, like with any tool, AI should not be allowed solely to guide human enterprises, “particularly when the risks of harm can be fatal.”

The proposal arrives amid growing concern among policymakers, military planners, and technology experts about the increasing role of artificial intelligence in combat operations.

Significantly, these concerns are no longer theoretical. As The Debrief previously reported, Israel’s reported use of the AI targeting system “Lavender” in Gaza triggered renewed debate over how much trust militaries should place in algorithmic target selection, particularly when civilian lives may be at risk.

Other recent examples have added to the concern, including studies showing that AI models can escalate dangerously in simulated war games, as well as the Pentagon’s continued push toward autonomous drones, AI-controlled aircraft, and robotic battlefield systems.

Even Pope Leo XIV recently weighed in on the issue in Magnifica Humanitas, his first encyclical, or formal papal teaching letter, warning that autonomous weapons could make war more feasible and less subject to human control, and arguing that lethal decisions must not be delegated to opaque or automated processes.

While the Pentagon has repeatedly stressed its commitment to responsible AI development, the HALO Act would codify many of those principles into law and create new statutory requirements governing how military AI systems are designed, tested, approved, and monitored.

Among the bill’s most significant provisions are requirements that autonomous weapon systems operate within predefined geographic areas, target sets, and timeframes. If a system cannot complete an engagement within those authorized parameters, it would be required to terminate the engagement until additional human operator and commander review is completed.

The legislation also calls for extensive record-keeping, cybersecurity protections, and continuous oversight to guard against unintended engagements and hostile manipulation.

The bill would also require senior Pentagon officials to conduct formal reviews before AI-enabled weapons enter development and again before they are fielded. Those reviews would assess legal compliance, operational safety, reliability, cybersecurity, and risks to civilians and protected infrastructure under the Law of Armed Conflict.

Beyond battlefield autonomy, the legislation targets several controversial uses of artificial intelligence in national security. It would prohibit covered Defense Department AI capabilities from inferring a person’s religion, race, political identity, sexual orientation, or emotional state. It would also restrict the purchase or receipt of Americans’ personal data from data brokers or other third-party sources when that data was obtained in a manner that would violate the bill’s rules.

Perhaps most notably, the proposed HALO Act explicitly forbids removing humans from decision-making processes involving presidential actions related to nuclear weapons.

“No covered artificial intelligence capability may be used with the intent, purpose, or outcome of… removing a human from the chain of decisionmaking for actions critical to informing and executing decisions by the President, including initiating or terminating nuclear weapons employment,” the proposed bill reads.

The measure also includes whistleblower protections for personnel working on military AI systems, mandates regular reporting to Congress, and requires the Pentagon to identify and remediate any fielded systems that fail to meet the law’s requirements.

Existing autonomous systems would undergo a comprehensive review, and any system found to be noncompliant could face retirement, modification, or suspension pending corrective action.

While the bill includes exemptions for certain defensive systems, cyber capabilities, mines, and other categories of military technology, its wider message is that as artificial intelligence becomes more deeply integrated into national defense, Congress wants humans, not machines, to remain responsible for high-stakes decisions.

The HALO Act is not the only effort underway on Capitol Hill to establish guardrails around military AI.

In March, Senator Elissa Slotkin (D-MI) introduced the AI Guardrails Act. Last week, Senator Kirsten Gillibrand (D-N.Y.) introduced separate legislation that would similarly prohibit the Pentagon from using artificial intelligence to launch nuclear weapons, conduct warrantless surveillance of Americans, or deploy fully autonomous weapons.

“Right now, the Pentagon is moving toward deploying incredibly powerful AI technology without commonsense guardrails in place, which could have catastrophic consequences that make all of us less safe,” Sen. Gillibrand said in a statement. “We must act now – not to stifle technological progress, but to establish clear rules of the road that keep humans in charge and keep AI’s use in warfare smart and safe.”

The competing proposals could set the stage for a broader congressional debate over the role of artificial intelligence in future military operations, particularly if lawmakers seek to incorporate them into the Fiscal Year 2027 National Defense Authorization Act (NDAA).

Before that can happen, however, the HALO Act and similar proposals must navigate the legislative process. The bills will first be considered by the relevant Senate committee, where lawmakers may hold hearings, debate their provisions, amend the text, or decline to advance them. If approved, it would then need to pass both the Senate and the House before being sent to the president for signature, either as a standalone measure or as part of a larger NDAA.

“My legislation would protect Americans from unlawful domestic surveillance, ensure that humans in the chain of command exercise responsibility for the use of any lethal technology, and maintain strong ethical protections in the deployment of autonomous and semi-autonomous weapons,” Sen. Schiff said in a statement.

Tim McMillan is a retired law enforcement executive, investigative reporter and co-founder of The Debrief. His writing typically focuses on defense, national security, the Intelligence Community and topics related to psychology. You can follow Tim on Twitter: @LtTimMcMillan.  Tim can be reached by email: tim@thedebrief.org or through encrypted email: LtTimMcMillan@protonmail.com 

A multi-institutional team of researchers led by University of Connecticut Professor Zhe Zhu has developed a method for measuring the dynamic, real-time activity of urban environments from space, which they are calling an “Urban Pulse.”

The research team behind the novel urban activity metric said that monitoring a city’s Urban Pulse could help mitigate uncontrolled urban sprawl or decay and enable environmentalists and urban planners to intervene before disasters become unavoidable.

Measuring an Urban Pulse Could Reveal Neighborhoods ‘Not Doing Well”

Although environmentalists and urban planners have a wide range of tools to measure the activities within a city, Zhu notes that scientists have spent decades merely capturing the “outcome of urbanization,” such as a finished road or a newly completed home. However, the researcher and lead author of a study detailing the Urban Pulse methodology added that, even with all the current tools, “you don’t really see the dynamics within an urban area.”

According to a statement detailing the new approach, a city’s pulse is determined by all construction activity within it. Along with new construction, the metric includes repairs, infrastructure improvements, or expansion into previously undeveloped green spaces. When used correctly, the researchers said that it can help determine “if and where their city is not doing well.”

“This would allow (authorities) to be proactive rather than conducting a metaphorical autopsy after the decay of an area is evident,” the team explained.

Bridging the Gap Between Abstract Urban Theories and Measurable, Real-World Data

To test their approach, the team evaluated the Urban Pulse of six cities: Seattle, Shenzhen, Lagos, Mumbai, Dubai, and Mexico City. This involved a deep examination of what the team termed “decades of dense time-series data” collected by NASA’s Harmonized Landsat and Sentinel-2 (HLS)  satellites for physical transformations in an urban environment, such as new construction, measurable infrastructure improvements, and demolition.

Instead of analyzing each city’s changes manually, the team evaluated the above changes on what they called “the neighborhood level” using a deep-learning and time-series-analysis approach called CAPES, developed by former UConn postdoctoral researcher Ji Won Suh. The team said that, by observing these “high-frequency rhythms of development” from a broad ‘outer space’ perspective, their approach “bridges the gap between abstract urban theories and measurable, real-world data.”

After examining CAPES’ results, the team found several key markers within the Urban Pulse. For example, the view from space revealed that growth within cities is not smooth and steady. Instead, Zhu and colleagues said that development happens in “abrupt, intense, and episodic bursts of construction.”

CAPES also revealed that the rhythms of an urban environment are cyclical. For example, while a city may show relatively steady growth on a broader level, individual neighborhoods go through “dramatic boom-and-rest cycles” of expansion and dormancy that don’t appear to follow predictable annual seasons.

The third pattern revealed by measuring the six cities’ Urban Pulse from space was that cities are “asynchronous,” meaning a single city does not ‘beat’ in unison. The team noted that neighborhoods “pulse at completely different times.” When it functions properly, this “uncoordinated rhythm” helps prevent the city’s infrastructure and labor markets from “overheating.”

Unlike previous methods for tracking a city’s evolution, the team noted that their Urban Pulse approach can help researchers “visualize a city’s reaction to global shocks.” For example, the team said that their analysis captured “the exact moment the COVID-19 pandemic triggered a widespread, synchronized ‘cardiac arrest’ in urban development worldwide.”

However, their new tool also revealed what the researchers termed “profound inequalities” in how individual cities recovered from the dramatic halt to urban growth. For example, the team said that the Urban Pulse of Shenzhen revealed synchronized ‘dips’ in activity, followed almost immediately by “rapid, policy-driven rebounds.” However, the same Orban Pulse analysis showed that the reactions in Mumbai and Mexico City were much more “muted.”

“It’s like in human beings,” Zhu explained. “When you get a disease, it’s not going to show up exactly the same in different people.”

A ‘Very Impactful Tool’ for Navigating Cities

Although the Urban Pulse metric offers a tantalizing tool for academics, the team noted real-world benefits for global policymakers, urban planners, and environmentalists, adding that “it serves as an early warning system.”

“By monitoring the rhythm, rate, and amplitude of neighborhood pulses, governments can identify early signs of urban decay or unsustainable sprawl and intervene before crises become entrenched,” they explained.

The team also suggested that making Urban Pulse data publicly available could “revolutionize how everyday people interact with their cities.” For example, an urban family considering a move to a new city or a new part of their current city could track a target neighborhood’s pulse to spot early warning signs of decay or early indicators of positive-trending growth. The same data could help business owners plan new locations or expanded service routes, depending on the business profile and the local Urban Pulse trends.

“This is going to be a very impactful tool influencing not only top-down policy decisions from governments but also bottom-up decisions from everyday people navigating their cities,” Zhu explained.

In a recent study, “The Urban Pulse: Diagnosing the urbanization process as spiky, cyclical, and asynchronous” was published in the Proceedings of the National Academy of Sciences.

Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.

For years, people around the world have reported being disturbed by a low, persistent droning sound of unknown origin.

Often described as more of a vibration than a specific tone, this sound has become widely known as “The Hum,” a phenomenon that is more frequently reported in certain cities and specific areas than others.

Over time, possible explanations have included industrial ventilation systems, military sonar experiments, and, in some online discussions, extraterrestrial signals, although none of these theories are supported by evidence.

However, in a recent study from the Norwegian University of Science and Technology (NTNU), published in PLOS ONE, researchers now offer evidence that, for most people who experience this phenomenon, the source is probably not external, but instead may actually originate within their own auditory system.

From Bristol to Taos and Beyond

Residents of Bristol, England, first widely reported The Hum in the mid-1970s, when the Bristol Evening Post received several reports from people who claimed they experienced hearing a strange, low sound. People initially thought the industrial fans in an area warehouse were responsible, but the hum persisted after the warehouse shut down.

By the 1990s, reports of a similar phenomenon began surfacing in Taos, New Mexico, where residents described a persistent, diesel engine-like rumble. Both state and federal authorities investigated the sound but could not explain it. The Taos Hum became one of the most studied and widely recognized examples of this phenomenon. Since then, similar reports have come from Canada, Australia, New Zealand, South Africa, and several European countries.

As reports grew, people proposed explanations ranging from ocean-generated infrasound to military sonar and CIA transmitters. Some online discussions have even suggested alien technology as a possible cause. In 2012, Canadian teacher Glen MacPherson, who first experienced The Hum on the west coast of British Columbia, created the World Hum Map and Database Project to document cases worldwide. The project has since collected thousands of entries.

Testing Two Hypotheses

To investigate the phenomenon, Professor Markus Drexl at NTNU recruited 28 people in Germany who all reported hearing a persistent, unexplained humming sound. Clinicians refer to this as a low-frequency sound percept, or LFSP. Most participants described the sound as having a frequency around 50 Hz, about the same as a deep mechanical rumble.

The research team tested two main explanations: whether participants had unusually acute sensitivity to low-frequency sound, or whether some were perceiving sounds generated by their own inner ears.

“We know that there are people who hear low-frequency sounds that can actually be measured, even if other people don’t hear them,” Drexl said. “But it’s not so easy to find the source of these sound waves, because it’s a struggle to localize low-frequency sounds.”

What the Ear Produces on Its Own

The cochlea, a spiral-shaped structure in the inner ear that converts sound waves into neural signals, also actively amplifies incoming sounds. This amplification produces faint sounds emitted from the ear, known as spontaneous otoacoustic emissions (SOAEs).

Most people are not aware of these emissions. In rare cases, people perceive SOAEs as tinnitus. Drexl’s team investigated whether people who hear the Hum might be detecting a low-frequency version of this phenomenon.

The results did not support this idea. The team found no low-frequency SOAEs in any participant. The hypothesis of unusually acute low-frequency hearing was also not supported; while a few participants had slightly better low-frequency hearing than average, most did not.

“Even though the group we tested was small, it still means that the hypothesis of having especially good hearing for low-frequency sounds does not hold for most people,” Drexl said.

When the Sound Has No Source

This left a third group: participants who reported hearing something that no external instrument could detect. “Then there are people who hear something that cannot be measured objectively. We believe people in this category have a form of low-frequency tinnitus,” Drexl said.

The Hum differs from typical tinnitus because most people who experience it first believe the sound comes from an external source, sometimes spending years searching for its origin before realizing it is internal. The researchers still have not ruled out external causes completely. In some cases, near industrial sites or coastlines, genuine low-frequency sources may exist. However, researchers identified no external source for most participants in the study.

“Based on our results, although we haven’t ruled out cases of physical external sound sources, we suggest that subjective tinnitus in the low-frequency range is often the cause of hearing pulsations of low-frequency sound perceptions,” Drexl said.

The Blind Spot in Auditory Research

The study also highlights that the low-frequency range of the auditory system remains poorly understood in hearing science.

“What we know about the hearing system is mainly based on how we capture and process sound with higher frequencies. We know less about how the auditory system handles and processes low-frequency sound, or infrasound,” Drexl said.

Although the cause of well-known cases like the Taos Hum remains unresolved, the new findings suggest that many reports of unexplained low-frequency sounds may actually originate from within the auditory system rather than from an external source.

Austin Burgess is a writer and researcher with a background in sales, marketing, and data analytics. He holds an MBA, a Bachelor of Science in Business Administration, and a data analytics certification. His work focuses on breaking scientific developments, with an emphasis on emerging biology, cognitive neuroscience, and archaeological discoveries.