Rubino recently chaired a team of 56 experts that was assembled to better define obesity and develop new diagnostic criteria for the condition. First proposed in January 2025, their new framework includes more body measurements beyond BMI and distinguishes between "preclinical" and "clinical" obesity.

Now, a new study published Wednesday (Nov. 11) in the journal Nature confirms that these new criteria could detect obesity with greater precision than BMI alone. In other words, with the new approach, more people would be accurately diagnosed with obesity and fewer people would be misdiagnosed than are with BMI alone.

Live Science spoke with Rubino and other experts to break down the new findings and learn what they mean for patients.

What are the limitations of BMI?

At the simplest level, obesity is excess body fat. There are special scans and exams that send weak electrical signals through the body to measure a person's body fat percentage directly, but criteria based on body measurements are more accessible across clinical settings.

BMI is the most common of these measurements, as it simply involves dividing a person's weight by their height squared. However, it does not account for individual differences in lean muscle mass or bone density.

Additionally, the different BMI categories — such as "overweight" and "obese" — don't carry the same risks for all patients. Certain racial and ethnic groups tend to experience health consequences, such as higher mortality rates, at different BMI levels than others do.

What metrics does the new obesity definition use?

For a given patient being assessed for obesity, the proposed guidelines would suggest using at least one additional body measurement alongside BMI and having their doctor review their medical history for other signs of bodily or organ dysfunction.

The proposed body measurements are less influenced by a person's muscle mass or bone structure than BMI is. They include waist circumference, waist-to-hip ratio and waist-to-height ratio. Notably, because different ethnicities are associated with different fat distribution patterns in the body, the latest Nature study incorporated different waist circumference cutoffs based that varied by ethnicity.

In addition to these body measurements, the proposed criteria look at 18 conditions and signs of bodily or organ dysfunction that are related to obesity, such as cardiovascular diseases, joint pain and sleep apnea. (All 18 factors can be found detailed in this chart.)

What is the difference between preclinical and clinical obesity?

Rubino and his colleagues — which together made up what's known as a Lancet Commission — defined "clinical obesity" as a disease state involving at least one of 18 forms of bodily dysfunction caused by excess fat tissue. Preclinical obesity, by contrast, is when a person is at risk of this disease state and may need interventions to avoid obesity-related dysfunction.

That means that two people with the same BMI, waist circumference and waist-to-height ratio may be classified differently, depending on whether they have other conditions. In the new study, between 77% and 91% of individuals with preclinical obesity did not progress to clinical obesity within 10 years, depending on the cohort analyzed.

This distinction can be complicated, though, as the diagnostic metrics for each form of dysfunction contain their own ambiguities.

"There needs to be more consensus on what's actually defining clinical obesity," said Dr. Aayush Visaria, an internal medicine instructor at Rutgers Robert Wood Johnson Medical School in New Jersey. Visaira was not involved in writing the new criteria but authored an analysis of the proposed measures.

The Lancet Commission argues that the categories of preclinical and clinical obesity could help doctors identify the people with the greatest need for treatment. The researchers tracked health outcomes using electronic health records from China, the United Kingdom, the United States and Spain, and they determined that their clinical obesity classification was better at flagging people's risk of death than BMI alone.

They found no clear association between BMI and mortality risk, but clinical obesity was linked to a 69% greater risk of all-cause mortality, compared to no obesity.

Would the new criteria affect the overall prevalence of obesity?

The Lancet Commission's approach could drive a small net uptick in individuals diagnosed with obesity, according to the new study.

Under the current framework, "we are definitely missing some people who actually need obesity treatment but just did not meet the BMI criteria," said Dr. Jennifer Hwang, an instructor of medicine at the University of Chicago who has published her own analysis of the new criteria.

With the BMI-only approach, people with BMIs of 30 or higher are categorized as obese. With the new definition, some people with BMIs under 30 would be newly categorized as clinically obese, while a smaller group of people with high BMIs would suddenly not count as clinically obese, the Nature study predicted.

For instance, the former group might include people who have "overweight" BMIs but also have obesity-related dysfunction, while the latter group might include people with "obese" BMIs but without any dysfunction.

Overall, the new criteria would increase obesity prevalence by about 3.3% to 7.4%, the team predicted. The percentage varied depending on the group analyzed.

What would it take to implement this new definition?

More research is needed to prove that the Lancet Commission's criteria would improve patient care and be practical to use in a clinical setting, Hwang said. She noted potential challenges in implementing both new aspects of the new framework. While the body measurements sound simple enough to use, clinicians would need training to perform them accurately.

Providers also may struggle with the new distinction between preclinical and clinical obesity. A 2025 analysis of the Lancet Commission framework noted that some patients who qualify for obesity medications under the Food and Drug Administration's guidelines may be recharacterized as having preclinical obesity and no longer receive a prescription.

Rubino and the rest of the Lancet Commission plan to continue validating their framework to see how it could best support personalized obesity treatment. For instance, they want to determine which forms of organ dysfunction are of greatest concern and develop a way of scoring each patient's level of risk.

This article is for informational purposes only and is not meant to offer medical advice.

Help us improve Live Science Pro: We're always trying to make our content better. Leave us feedback about Pro here.

'> More people could count as obese under newly proposed definition — here's what you need to know Nancy Grace Roman Space Telescope is nearing its final destination more than 1 million miles (1.6 million kilometers) from Earth, where it will soon scour the universe for a host of cosmological treasures, including an estimated 100,000 new alien worlds.

But even before its mission truly begins, recent developments suggest the state-of-the-art spacecraft could take better images than — and remain operational for more than twice as long as — initially expected, further delighting already-excited astronomers.

"It is fantastic to learn that Roman is not just reaching its design goals but exceeding them," Eamonn Kerins, an astronomer at the University of Manchester in the U.K. who will help lead one of Roman's major surveys, told Live Science.

Roman is NASA's latest flagship space telescope, following in the footsteps of iconic observatories like the Hubble Space Telescope and the James Webb Space Telescope (JWST). The $4 billion machine ‪—‬ which is over 42 feet (12.7 meters) long and weighs around the same as a fully grown Tyrannosaurus rex ‪—‬ successfully launched into space on Aug. 30, more than a decade after scientists started building it.

The telescope is now en route to Lagrange point 2 (L2), a fixed point relative to our planet where Earth's gravity and the sun's gravity cancel each other out. There, Roman will join several other important spacecraft, including JWST and the European Space Agency's Euclid telescope.

During Roman's journey to L2, which is currently around 85% complete, mission scientists have remotely switched on the telescope's various instruments to test whether they function as expected. So far, this "commissioning process" has gone off without a hitch, and by the time Roman arrives in less than two weeks, it should be ready to snap its first in-depth images of the cosmos.

Researchers were already pumped to see what Roman will be able to do once it is in place and fully switched on. However, that excitement has further intensified in recent weeks, thanks to two postlaunch developments.

First, a series of near-perfect rocket burns, executed during and shortly after launch, saved more than a decade's worth of fuel that can now be used to extend Roman's mission. Second, after remotely adjusting the telescope's mirror, researchers discovered it should be capable of snapping images with around 30% greater detail than engineers predicted.

The team that designed, launched and remotely commissioned the orbital observatory has "done an amazing job" and "their work has ensured that Roman is more than up to the task," Kerins said.

Extended lifespan

Shortly after Roman arrived in space on board a SpaceX Falcon Heavy rocket that lifted off from NASA's Kennedy Space Center in Florida, mission scientists conducted two major burns, or engine firings, which gave the spacecraft enough momentum to escape Earth's orbit and make the journey to L2.

Thanks to a combination of "exquisite planning by our orbital dynamics team" and "brilliant execution by the operations team," these burns were so precise that each one saved up to four years' worth of fuel, Jamie Dunn, director of NASA's Goddard Space Flight Center in Greenbelt, Maryland, said in a Sept. 14 statement.

On top of this, Roman ended up being much lighter than initially planned, which allowed engineers to pack another four years' worth of fuel into the spacecraft before launch. "Since Roman's [weight] was lower than we budgeted for, we were able to fill the propellant tanks to their capacity rather than only filling them as much as we needed," Alison Rao, the Roman propulsion lead at NASA Goddard, said in the statement.

In total, these savings could give Roman an additional 12 years of fuel, which could more than double the mission's planned 10-year lifespan. That means Roman could still be capturing images of the cosmos in 2048.

Given that Roman can collect data up to 1,000 times faster than Hubble, this extended lifespan will greatly enhance the amount of data the new space telescope will be able to capture. "With a 20-year Roman lifetime, we could, in theory, do over 20,000 years of Hubble survey work," Kerins said. "That's a lot of science!"

This prolonged lifespan will let astronomers compare images of specific objects decades apart — such as expanding nebulas or colliding galaxies — allowing them to detect changes they otherwise might have missed.

It may also let them study objects or phenomena that we haven't even discovered yet, which is particularly exciting, Kerins noted. "The real show-stopper results will be new things we just aren't even thinking about right now," he said. "The possibilities are truly breathtaking."

There is also the chance that Roman's mission could be extended even further, because engineers often find clever ways of making active spacecraft last longer. For example, Hubble is more than two decades past its initial mission parameters, and the recently deceased Swift Observatory lasted 10 times longer than initially predicted before falling back to Earth last week.

Improved image quality

Roman's secret weapon is arguably its Wide Field Instrument (WFI), made up of a 288-megapixel camera attached to a 7.9-foot (2.4 m) mirror, which will capture ultra-detailed images with a field of view roughly 100 times larger than Hubble's.

We have already seen the first WFI images — a series of blurry, green dots captured during a test of the instrument's 18 different light detectors ( see below). However, those photos were nothing like what WFI will capture in the future; those images will be so detailed that you would need dozens of high-definition TVs to properly display a single snap in full resolution, Kerins said.

After Roman completes the initial WFI commissioning phase, those images will be around 30% sharper than designers predicted. "All of the images from Roman's cosmic surveys will be even sharper than we expected," Alden Jurling, a senior optical engineer who works on Roman at NASA Goddard, said in an Oct. 14 statement. "It's a great outcome."

The improvements were first noticed after the WFI's car-sized mirror was realigned by just one-sixteenth the diameter of a human hair, demonstrating just how intricate the commissioning process has been. "Calibrating an instrument is like tuning a piano or guitar before a concert," Maxime Rizzo, a WFI systems engineer at NASA Goddard, said in the statement. "You adjust everything until it's just how you want it and then leave the settings alone so it performs consistently while you use it."

The improved image quality could really come to the fore during Roman's hunt for potentially habitable exoplanets, which is what Live Science's readers are most excited about for this mission.

Kerins, who is leading the Exoplanet Demographics Working Group for the Transits in the Roman Exoplanets Survey, is particularly excited about this development, but he said it does not necessarily guarantee that Roman will find more exoplanets than initially predicted.

"A remarkable achievement"

The rest of Roman's commissioning phase is also proceeding as planned.

Roman's coronagraph instrument, which will block out the light from distant stars to allow WFI to spot alien worlds, has passed its main commissioning phase and is working as intended, according to a NASA blog post.

Meanwhile, a global network of ground stations, which will receive up to 1.4 terabytes of data from Roman every day, has established contact with the spacecraft and is receiving signals as expected, another blog post revealed.

All of these early wins raise hopes that Roman can have a long and successful career, and are a testament to the years of work that went into designing the spacecraft and planning the mission.

"What we're seeing now with the actual optical performance and estimated lifetime of Roman is just how good that design process has been," Kerins said. "It's a remarkable achievement. I can't wait to see what Roman is going to give us."

'> 'The possibilities are truly breathtaking': NASA's Roman Space Telescope will take better images and last longer than experts predicted peritonitis, can spread to the bloodstream and cause the life-threatening condition sepsis, which kicks the immune system into overdrive.

Even though the patient had acute pain in his lower-right abdomen, he did not show signs of peritonitis, such as fever, nausea, symptoms of dehydration and an elevated heart rate, according to a report of his case. His doctors then performed abdominal ultrasound scans and found that the man's abdominal organs, including the appendix, appeared normal, with no signs of inflammation.

The report's authors did not include details about the man's treatment after this examination. But eight months later, he was still in pain and returned to the hospital for further evaluation, they noted.

The diagnosis: This time, when medical personnel questioned the man, he recalled that approximately 15 years earlier, he had accidentally swallowed a piece of a long bone containing edible marrow. The report does not mention if the man sought treatment immediately after swallowing this bone.

At this second visit, doctors performed an abdominal X-ray and found a round object near the upper right of the man's pelvis. It measured about an inch (2.5 centimeters) long and a little over an inch (3 cm) wide.

According to a subsequent CT scan, the object contained bone tissue and was near the appendix. When the doctors looked inside the patient's abdomen with a laparoscope — a long, flexible tool with a camera at one end — they saw that the appendix was enlarged.

The treatment: Surgeons performed a laparoscopic appendectomy, which uses small incisions in the abdomen to insert instruments for removing the appendix. Inside the appendix was a hardened mass of fecal matter, called a fecaloma, which surrounded a long bone.

The organ's muscular walls had been stretched out by the mass, but there were no signs of inflammation. No complications developed after the surgery, and the patient was discharged two days later. The report does not describe any follow-up visits or treatments.

What makes the case unique: It's relatively uncommon for people to accidentally swallow something indigestible and then require a medical visit for it. In the United States annually, about 120,000 people — roughly 90% of whom are children — are treated for ingesting foreign objects, and most of the objects are swallowed accidentally. Most commonly, the adults requiring treatment have ingested jewelry, while children are more likely to swallow coins, toys and batteries.

Typically, small, swallowed items pass harmlessly through the intestines within 48 hours; less than 1% require surgical intervention. Some objects, however, need immediate attention. For example, sharp items can tear the esophagus or puncture digestive organs. Batteries are hazardous if swallowed, as they contain corrosive acid that can leak into the gut. And small magnets are a big risk, especially if two or more are involved, since they may stick together through intestinal walls, which can tear holes in tissues or cause blockages and contortions in the intestines.

Swallowed foreign bodies rarely affect the appendix. Whether they enter the organ depends on the size of the opening into the appendix where it connects to the colon (which can vary between individuals), the dimensions of the ingested object, and the appendix's position in the body at the time. These objects cause approximately 0.005% cases of appendicitis, according to the man's case report. Such items recovered by surgeons through appendectomies include pieces of coal, nails, bits of enamel and glass, shells, dental crowns and bullets.

When a foreign body migrates to the appendix, it typically generates appendicitis within a few months, at most. However, this is not always the case. One report described a man who had eaten pigeons as a child and discovered more than 30 years later that he had 27 lead shot pellets in his appendix. Despite containing these pellets from the birds' flesh, his appendix was not inflamed.

"It is therefore possible, although rare, that a foreign body in the appendix even after many years (in our case, 15 years) does not lead to an authentic appendicitis either histologically or clinically," the authors of the marrowbone case report wrote.

They added that their patient was the first record in the scientific literature of a sizable bone lingering inside an appendix for more than a decade without causing significant inflammation. His pain was likely caused by physical shifting of the hard mass. His experience presented "a unique clinical picture," the doctors wrote.

"This case could offer a possible diagnostic and therapeutic option for appropriately treating patients with foreign bodies within the appendix," they said.

For more intriguing medical cases, check out our Diagnostic Dilemma archives.

This article is for informational purposes only and is not meant to offer medical advice.

Can you guess the diagnosis in these strange medical cases? Find out with our diagnostic dilemma quiz!

'> A man swallowed a bone, and‬ 15 years later, doctors found it in his appendix AI company, SpaceXAI (soon to be SpaceXSI), describes its Colossus cluster as the world's most powerful AI training system, comprising 200,000 interconnected chips.

Traditionally, the AI chips used to train foundation models are housed in separate servers and communicate over a network to share data and divide workloads. But the new architecture, Peerium, uses a high-speed interconnect system designed to maintain efficient communication between chips across multiple racks, even as the number of chips scales into the hundreds of thousands.

Huawei unveiled the new architecture Sept. 17 at the company's annual CONNECT conference.

Representatives from Huawei said in a statement that computers powered by Peerium could train models with up to 40 trillion parameters. For comparison, competing hardware, like GB200 NVL72 from NVIDIA and CS-3 from Cerebras, have reported training at the trillion-parameter scale, rather than the tens-of-trillions.

"Over the next two years, there will be roughly 6 or 7 frontier AI labs in China, and all will aim at training foundation language models of sizes ranging from 10 to 40 trillion parameters," Liao Heng, chief scientist for Huawei's chip design arm HiSilicon, told the Associated Press. "So you need such a scale of infrastructure to train these models."

The technology powering Peerium

Peerium's performance relies on three elements: nested parallelism, unified memory addressing, and peer-to-peer interconnects, Huawei representatives said in the statement.

Nested parallelism allows workloads to be broken into smaller tasks and organized across hierarchical groups of chips that work in parallel. It's similar to how a company breaks down work into departments and then smaller teams, all of which coordinate their efforts toward a common goal. Unified memory addressing allows processors to access memory across other servers, as opposed to only that attached to the processor's own server. Peer-to-peer interconnects allow components to communicate more directly with one another, rather than relying on an intermediary.

All three principles are designed to make more efficient use of computing resources so that a single system can coordinate larger numbers of chips to handle demanding AI workloads.

According to Huawei, existing interconnect technologies — which link processors and servers to enable them to communicate — cannot support the Peerium architecture at the scale it envisages. For instance, NVIDIA uses NVLink for communication within racks and InfiniBand for communication between racks. The inter-rack communication bandwidth in this setup is 200GB per second, Eric Xu, Huawei's rotating chairman, told the AP.

"With such a low inter-rack communications bandwidth, there is no way you can make one million processors work as one computer," he said.

Huawei instead developed its own interconnect technology, UnifiedBus, which the company says delivers inter-rack communications bandwidth of up to 800GB per second.

"When one million processors work as one computer, this lays the foundation for better and more efficient AI training and inference," Xu added. "Therefore, I see UnifiedBus as the path for the future AI era. I believe, in the years to come, other players would certainly follow suit."

Stitching together a computing network

Alongside Peerium, Huawei also announced the Atlas 950 SuperPoD, a computing system built on Peerium and powered by more than 8,000 Huawei Ascend 950DT AI accelerator chips.

Xu said testing for AI training is underway on these SuperPoDs and that results show that they use their available computing power for AI training more efficiently than AI computing clusters that aren’t based on Peerium and UnifiedBus.

Huawei expects to begin supplying the SuperPoDs by early next year, at the latest, before its SuperClusters, which link multiple SuperPoDs to form a larger AI computing system, based on Peerium, eventually come online. Representatives said that one SuperCluster with 256,000 computing cards — hardware modules that add processing capacity — is currently being deployed and tested.

Models with large numbers of parameters demand greater computing resources and infrastructure, which isn't always desirable as it increases costs. In the summer, researchers used an IBM quantum computer to reduce the perplexity of Meta's Llama 3.1 8B language model — a measure of how well it predicts the next word or token — while keeping the number of parameters almost unchanged.

'> Huawei unveils 'SuperCluster' architecture designed to make 1 million AI chips work as a single computer

In this excerpt from "This Is Life: A Journey from Inside Your Body to Beyond Earth" (University of Chicago Press/Picador, 2026), author and physicist Christophe Galfard looks at the progression among scientists who were coming to realize that thermodynamics was an essential piece of this long-standing puzzle.

Some two and a half centuries ago, the foremost experts on scientific matters knew a thing or two about heat. They knew, for instance, how heat could be transferred from one place to another. A new science was about to emerge out of this knowledge, a science called thermodynamics, which means "movements of heat" in Greek.

Thermodynamics isn't a force. It is more like a guidebook, a set of rules that apply to large

numbers of particles when they come together. It gives us, humans, a way to understand how particles behave when there is a lot of them without needing to refer to each one of them individually. It shows us how properties that don't exist on their own arise when many particles are together. It deals with these things we call emergent phenomena, such as heat and pressure, and which [Philip] Anderson's "More Is Different" tried to make sense of.

Understanding the dynamics of heat meant a lot to nineteenth-century scientists — so much so that many saw in it the roots of a philosophy so universal and powerful that they thought it should guide us through all our lives. Some even went as far as believing that heat was the source of eternal life. A prominent scientist became so convinced that this was the case that he locked himself up in his house and overheated it, thus shielding himself from all mortal diseases (ageing and death included). The experience was a true torture for the occasional guests who came to visit him, not to mention his wife, who had to endure it day and night.

The scientist held fast to his belief, though, piling on layer after layer of clothing to keep himself ever warmer. Unfortunately, the bulk made it difficult to move, and he eventually missed a step on his own staircase and died from the fall.

As a scientific discipline, thermodynamics was born with a book written in 1824 by a 27-year-old French physicist named Nicolas Léonard Sadi Carnot, who, as he explained how heat could produce work, told everyone how the steam engine worked.

With Carnot's vision, the way hot objects cool down began to be understood, raising hopes that the resolution of one particular problem might be imminent: the determination of the Earth's age. Were we to somehow guess how hot our planet was at birth, thermodynamics could then be used to tell us how much time had gone by for it to have cooled to its present temperature. Many scientists tried it, keen to be the first one to nail the true age of our world.

Considering our planet in all its complexity to be far too difficult, simplifications were in order, and British physicist William Thomson shot first by picturing our world as a ball. A very simple, rock-solid ball made of pretty much the same stuff throughout, from surface to core. No ocean, no mountain, just a smooth ball the size of the Earth. He then calculated how long it would take it to cool down from being red hot to its present temperature, and declared that the Earth was something between 40 and 400 million years old.

Refining his calculations, he then announced that the world was 100 million years old, before settling for 40 million again.

Thomson's result does not correspond to the true age of the Earth, but it was a start. It was the result of a model, an attempt at figuring out something about our world using still-to-be-refined laws, and mathematical sense. What was more problematic was that no one dared question his results. Even as it shifted from one paper to another, the age of the Earth given by Thomson was always greeted as the right one. A reason for this is that at the end of the nineteenth century Thomson had become Lord Kelvin.

The same Kelvin after whom the Kelvin unit of absolute temperature is named. A scientific superstar who had the power to undo, in a snap of fingers, the career of anyone who disagreed with him.

Lord Kelvin was a physicist, not a geologist, so geologists could have questioned his work, but they didn't. In fact, they weren't bothered. Many of them back then believed that being a geologist was all about intuition and proper English, a language they deemed far more efficient than mathematical gibberish.

That being said, and however wrong the results, Kelvin's calculations were beautiful, giving whoever wanted to think about the problem of the age of the Earth a way forward, which is exactly what one of his former students, Northern Irishman John Perry, did. He thought that Kelvin had overlooked something. As a man of science talking to his former mentor (and job provider), Perry explained his vision to Kelvin but was ignored.

Still, he published his thoughts in Nature. But again, the article was ignored. Not just by Kelvin, but by the scientific community at large, including geologists.

It would have saved us all quite a bit of time had this not been the case, because Perry not only found a much more correct way to picture the Earth and estimate its age than Kelvin had, but he also found the source of the power that makes our planet's continents drift.

In his model, Perry didn't picture the Earth to be uniformly the same from surface to core as Kelvin had. Instead, he modelled the Earth's interior as being divided into three regions: a metallic core at its centre, a solid crust at its surface, and a mantle that lay in between the two. Rather unexpectedly, Perry didn't envision the mantle as everyone else would have; he believed that it didn't behave like the solid rock it was, but as a liquid.

No wonder his former master didn't take him seriously. However, he pictured the mantle behaving like a liquid only when considered over long periods of time. Sandwiched between a hot core and a colder crust that very much looked like a lid, he believed the mantle had no choice but to behave just like water does in a heated pan, with the hottest parts at the bottom rising and cooling before diving back down and rising up again, in repeated loops, albeit in extremely slow motion. This type of movement is called convection, and it happens in solids, too.

If he was right, there would be two immediate consequences. The first one was that the time it would take for our planet's surface to cool down from red hot to its current temperature could now be far longer than Kelvin had estimated. The lid and the convection patterns prevented our planet from quickly radiating away all its energy into space, so we were now inhabiting an Earth that could be as old as 2 or 3 billion years. Maybe even more. Such timescales were unheard of in the scientific community. Back then, no one knew that the universe itself was 13.8 billion years old. They knew next to nothing.

The second consequence of Perry's model was that the mantle's circular movements underneath the crust could drag the crust itself via friction. The solid surface of our world would then move, and split into pieces that would drift, and collide, and plunge underneath — or slide above — one another. Where they collided, mountain ranges would rise, like the Alps, the Himalayas, the Rockies . . . Where they split apart, rifts would appear, probably in the middle of oceans, along ridges . . . just like [Marie] Tharp had found.

Nowadays, these broken pieces of our planet's surface have all been mapped. They are our world's plates and their movements through time are called plate tectonics. Today, most of us have heard about plate tectonics. Back then, however, no one had, and if very few people remember Perry today, it is because another scientific breakthrough made the estimation of the age of the Earth much easier and precise, showing us that our world isn't 2 or 3 billion years old, as Perry suggested, but precisely 4.567 billion, give or take a few million.

Reprinted with permission from This Is Life: A Journey from Inside Your Body to Beyond Earth by Christophe Galfard, published by the University of Chicago Press in North America and Picador in the UK. © 2026. All rights reserved.

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'> 'No one dared question his results': How thermodynamics sparked a heated debate about Earth's age in the 19th century