The functions of these genes were already known, but their distinct expression in these two groups of cells was revealed by the new research. The cell populations remained distinct as they developed into full-fledged nervous tissue, rather than overlapping.

The team also examined chromatin, the molecular structure that packages DNA tightly inside the nucleus and helps regulate which genes a cell can use. The two cell populations show different chromatin configurations, the team found, which further supports the idea that they follow separate developmental pathways.

That may help to explain why scientists' attempts to grow hindbrain neurons have been largely unsuccessful.

"Previous attempts to make hindbrain neurons likely tried to coax forebrain and midbrain progenitors into hindbrain cells, which our study shows is not possible," study co-author Rayyan Jokhai, a graduate student in Loh's lab, said in a statement.

Why it matters

Using the information uncovered in their experiments, the researchers successfully guided human stem cells to transform into functional hindbrain motor neurons, which are involved in controlling movement. Specifically, these cells produced proteins characteristic of the hard-to-grow hindbrain regions that help control muscles of the face and those involved in swallowing.

In several neurological diseases, including spinal muscular atrophy and amyotrophic lateral sclerosis, motor neurons deteriorate and affected patients can lose their ability to swallow, speak and breathe independently.

"We cannot sample living motor neurons from a patient's hindbrain to watch how these diseases attack these neurons," Loh said. "Growing these hindbrain motor neurons in a dish gives us a way to investigate these diseases." Looking forward, the team aims to use their findings to study these diseases and pinpoint new treatments.

The new findings could also reveal something fundamental about the evolution of vertebrate animals.

The study authors investigated whether the two developmental pathways were unique to humans or reflected a much older evolutionary arrangement. They turned to previously published data on other species — including macaques (Macaca), zebrafish (Danio rerio) and chickens (Gallus gallus domesticus) — and again found two distinct cell populations expressing the two key genes.

And even in acorn worms — a marine invertebrate whose evolution diverged from vertebrates about 550 million years ago — they again found these two distinct groups of cells.

"The Stanford discovery establishes that the deep ancestry of the vertebrate brain is fundamentally modular," said Anna Di Cosmo, a professor of biology at the University of Naples Federico II in Italy who wasn't involved with the study. "The developmental separation between the anterior lineage (forebrain/midbrain) and the posterior lineage (hindbrain) is traceably ancient," Cosmo told Live Science in an email.

Loh's team speculates that these developmental trajectories seen in the womb may suggest that the two cell populations once belonged to two separate nervous systems. "Later in evolution, these two nervous systems may have been pushed together to give rise to the appearance of one integrated brain," Loh said.

However, the study doesn't reveal exactly when the two pathways arose or establish how they integrated. "It is important to emphasize that this is only an idea, and it might change as scientists learn more," Loh said.

See how much you know about the most complex organ in the human body with our brain quiz!

'> Is the brain actually 2 nervous systems smooshed together? A new study claims it is.

Petal will also be the first commercial subsea cable system to use multi-core fiber technology, according to the statement. Whereas conventional fiber strands typically contain a single core, each of Petal's fiber strands will contain two cores that carry optical signals in opposite directions, allowing a single strand to provide the capacity that would conventionally require a pair of single-core fibers.

Each fiber strand is roughly as thick as a human hair, measuring just 125 micrometers in diameter. Petal will contain 24 pairs of dual-core fibers, giving it 96 individual fiber cores in total and enabling it to carry as much data as 48 conventional fiber pairs, Meta engineers said.

Japanese technology company NEC will be responsible for the overall design and construction of Petal, while Sumitomo Electric will provide the fiber itself.

"Achieving petabit-per-second capacity across a transoceanic submarine system represents a major technological milestone in the history of global telecommunications," Eduardo Mateo, chief strategy officer of the Submarine Networks Division at NEC, said in the statement.

Bedrock of the internet

Subsea cables are among the most critical layers of internet infrastructure, carrying around 99% of the world's internet traffic, according to the International Telecommunication Union, the United Nations ​agency for digital technologies.

Installing thousands of miles of fragile glass cable on the ocean floor is an engineering feat in itself. Equally challenging is ensuring that these cables can carry the tiny pulses of infrared light that transport fiber-optic data across such huge distances without impacting performance.

This is typically achieved through repeaters — amplifiers installed at regular intervals along the cable that use lasers to boost the optical signals.

A 4,300-mile subsea cable typically needs about 100 of these repeaters to amplify the signals along its length, Meta representatives said.

Petal will incorporate something called "fan-in/fan-out" technology. As each two-core fiber strand enters a repeater, an optical interface routes the signal from each core into a separate single-core fiber strand so that each can be amplified independently. The amplified signals are then routed back into the two cores of the dual-core fiber before continuing along the cable.

Combined with its dual-core fiber, this feat of signal engineering will enable Petal to double its data-carrying capacity without requiring a proportional increase in power, Meta representatives said.

Petal is one of many subsea cable investments by Meta in recent years, including Marea in 2018, Amitie in 2023 and Anjana in 2025. Marea, the company's first transatlantic fiber instalment, supports 192 Tbps, meaning Petal will offer more than five times that capacity.

'> New 4,300-mile-long internet cable will shuttle data along the ocean floor at 1 million gigabits per second

Geologists don't have the level of detail required to pinpoint an exact highest peak hundreds of millions of years ago. "We're never going to get that granularity, unfortunately," Alan Collins, a professor of geology at Adelaide University in Australia, told Live Science.

However, clues in residual sediments lodged inside Earth's crust hint at the lost grandeur of primordial snowcaps and summits. Scientists study these crusts to understand how deep they went, which can reveal how tall ancient mountains might have been.

Mountains are really just parts of the continental crust that have been thrust upward as tectonic plates slowly crash together. This crust is very heavy, and there is much more to it than what you see on the surface; even the most spectacularly tall peaks, like Everest, are anchored in deep crust. Just as crust gets thrust up to form mountain peaks, it also gets pushed deep under the surface. Both Collins and Ziyi Zhu, a geochemist at Curtin University in Australia, compared mountains to icebergs, in the sense that only a bit pokes above the surface.

"We can argue or speculate that [the biggest mountain] was in a place where there were deep roots in the crust," Zhu told Live Science.

Geologists estimate that the Himalayas, for example, have a crustal column that goes down as far as 50 miles (80 kilometers). Compare that to Everest's elevation of about 29,000 feet (9,000 m), and the world's tallest mountain at most represents only 14% of the rock slab it's part of. That means there's a limit to how tall mountains can get before they collapse under their own weight.

The Himalayas began forming between 50 million and 40 million years ago from the collision between the Indian Eurasian continental plates. As far as mountains go, they are relatively young. And that's partly why they are still so tall. Tall, jagged mountains erode quickly over time, though the Himalayas are still growing as the two plates continue to collide.

Such continental collisions have happened countless times before, though. For example, the Transgondwanan Supermountain, an ancient range in what is now East Africa, began emerging some 650 million years ago when Africa and South America crashed into Arabia, India, Australia and Antarctica to form the supercontinent Gondwana.

Gondwana split up again, but evidence of these mountains in places like southern India, Sri Lanka, Tanzania and Kenya point to them being three times the length of the Himalayas. "If you walk around there now, you can see rocks that were at the bottom of this mountain belt," Collins told Live Science. On average, the crust is deeper than the crust of the Himalayas. "We think this is at least the scale of the Himalayas if not more," Collins said.

The crusts found in these areas also hint at how tall the mountains were, with sections that descend up to 18 miles (30 km) deep, despite half a billion years of erosion. "At some point, they were likely halfway down a crustal column that was 60 kilometers [37 miles deep]," Collins said. This means that the mountains above this base could have been as tall as Everest.

In the Himalayas, the tallest mountains sit around the rim of the Tibetan Plateau, which has the highest elevation on the planet, at about 3.7 miles (6 km) above sea level, on average. The Transgondwanan range may have had a similar plateau around southern Madagascar, meaning its rim would have been in eastern Madagascar, southern India and eastern Antarctica, Collins said.

Another candidate for the tallest mountains was the Grenville orogeny, which popped up with the formation of the supercontinent Rodinia starting about 1.3 billion years ago. Its remains can be seen around southeastern Ontario and northwestern Vermont. But less is known about this extinct range, Collins said, with some scholars arguing that it wouldn't have been as tall as the Transgondwanan range or the Himalayas.

Further back, some 2 billion years ago, the formation of the supercontinent Nuna (also called Columbia) also left evidence of truly giant mountains. Zhu's paper found evidence of this supermountain by examining the composition of zircon crystals left in the crust underneath this vanished range.

Look any further back, however, and the picture gets murkier. When Earth was hotter, mountains likely couldn't get as high because warmer crusts can support less weight, Collins said. Stable continental plates and rocks didn't start to form until about 4 billion years ago, and it took hundreds of millions of additional years for large continents to form.

For Zhu, the Nuna, Transgondwana and Himalaya ranges are currently the best candidates for holding the tallest mountains that ever existed. But it's likely impossible to pinpoint the highest specific peak, at least with current scientific methods. "It's an open question," Zhu said.

How much do you know about our blue planet? Test your terran knowledge with our Earth quiz!

'> Has there ever been a mountain taller than Everest? 21,000 years ago. But since Beringian sites are often the remains of small seasonal hunting camps and are scattered across a large geographic area, much is still unknown about the earliest people who called the Western Hemisphere home.

"I expected we'd find hunting tools and knapping [stone tool making] debris surrounding a hearth or two, but I had no idea that we'd stumble into a base camp with tens of thousands of artifacts," study first author Kelly Graf, an archaeologist at the University of Kansas, told Live Science in an email. "It was a total surprise!"

In a study published Wednesday (Oct. 14) in the journal Science Advances, Graf and co-authors detailed their discoveries at Shégˊ Xdaltthˊíˊ, focusing on the earliest occupation, which occurred around 13,800 years ago, as evidence of people "settling in" to their new territory.

The researchers found a hearth, a small pit, and a dirt stain where a wooden post had once stood, likely the remains of a lean-to or early tent house. Additionally, the archaeologists unearthed stone tools, bone needles and a pendant made from an antler. Nearby, they found an earth oven, which was full of charcoal and animal bones and was likely used to slow-cook meat for a large family group.

"The complex feature at Shégˊ Xdaltthˊíˊ represents the earliest potential case of a habitation structure in North America," the researchers wrote in the study. "Early Alaskans knew their surroundings well."

Cross-cultural links

The archaeologists were also surprised by the stone tools recovered at Shégˊ Xdaltthˊíˊ because they are distinctively shaped and unique to central Alaska. Known as diamond-shaped hafted bifaces, the tools were crafted from rhyolite and basalt and are similar to those typically found much farther west in Beringia, in modern-day northern Siberia. Additionally, obsidian artifacts discovered at Shégˊ Xdaltthˊíˊ reveal that people brought the volcanic rock to the site from a geological source hundreds of miles to the northwest.

Bones from more than a dozen wolf-like animals suggest a further connection to Asia, according to the researchers. An analysis of the jaw of one of the animals showed that it was not from a dire wolf (Aenocyon dirus) or from a Pleistocene Beringian or gray wolf (Canis lupus sp.) but rather a population of wolf-like animals unique to central Alaska. Current genetic evidence suggests that early domesticated dogs in North America came from Siberian wolves. The timing and geographical location of Shégˊ Xdaltthˊíˊ provides circumstantial evidence that the people may have been dog owners.

"Like humans, potentially, the canids of Shégˊ Xdaltthˊíˊ and other early Alaskan sites were recent immigrants from Asian Beringia," the researchers wrote.

Although Shégˊ Xdaltthˊíˊ reveals a relationship with sites in Asia, there is also evidence of connections with early American sites south of the Canadian ice sheets, according to the study.

One clue to these connections is the presence of bone artifacts in a sewing kit. The archaeologists found eight bone needle fragments at Shégˊ Xdaltthˊíˊ. Previously, the only recovered eyed needles had come from Paleoindian sites in temperate North America. Therefore, the needles from Shégˊ Xdaltthˊíˊ are the oldest needles ever discovered in the Western Hemisphere, and they reveal connections with sites farther south, according to the study.

Another clue is the pendant, which was crafted from antler. The pendant had a hole drilled at one end and was fashioned into a point at the other end. This piece of ancient jewelry is similar to personal adornment items found farther south in North America.

"The co-occurrence of these cultural features at the single site of Shégˊ Xdaltthˊíˊ is truly notable," the researchers wrote, and they "highlight the strong cultural connection between early Beringians and Americans."

It is still unclear whether the people at Shégˊ Xdaltthˊíˊ were traveling to make these connections. "It would be hard to pin down whether or not they were moving back and forth during a lifetime, but at least we can say there is a connection," Graf said.

Further work in Beringia is needed

Future excavations in Beringia could help archaeologists learn more about the earliest people in the Americas, according to Graf. "Alaska is a big place and so remote, so there are really just a few small areas that have been intensively investigated," she said.

Spencer Pelton, an archaeologist at the University of Wyoming who was not involved in the research, wrote in an accompanying perspective published in the journal Science Advances that early Indigenous sites in Beringia are key to understanding the peopling of the Americas.

"Shégˊ Xdaltthˊíˊ is remarkable because it is the oldest site in the Americas containing a large and rich assemblage of features, artifacts, and faunal refuse indicative of prolonged residential occupation, providing an unprecedented glimpse into the lives of North America's first residents," Pelton wrote.

Graf is already planning future archaeological excavations in the area. "We're hoping to bring some younger Alaska Native folks out with us in the coming summers," she said, as incorporating local knowledge is important to the project. "Two of our co-authors are elders from Alaska Native corporations nearest to the site," she said. Elders named the Shégˊ Xdaltthˊíˊ site and have visited it to discuss where to excavate and what the archaeologists might find.

There is much left to learn about what was happening in Beringia 14,000 years ago, the researchers wrote, particularly since there are currently only two archaeological sites — including the 24,000-year-old Bluefish Caves site in the Yukon — that suggest humans were settling in Beringia considerably earlier.

How much do you know about the first people to reach the Americas? Find out with our First Americans quiz!

'> Archaeologists discover the oldest dwelling in the Western Hemisphere at a 13,800-year-old site in Alaska

Decades later, physicists found that Bethe's method also works for larger particles moving along a line, such as atoms. If those particles attract each other, the math predicts they will bind into clusters called Bethe strings.

Now, physicists have found evidence of these clusters in a line of ultracold atoms. The findings were published Aug. 29 in the journal Nature Communications.

The discovery may not create new gadgets, but it addresses a fundamental mystery in physics. Everything around us, from magnets to phone chips, consists of countless interacting particles. This makes their behavior difficult to predict. Ultracold atoms serve as a clear and adjustable way to study these complex systems.

A "necklace" of atoms

Researchers have spotted small Bethe strings before, in magnetic crystals and superconducting quantum circuits ‪— but those experiments captured strings one at a time.

Theory predicts that crowds of strings, in many sizes, can change how an entire system behaves, and studying that idea requires making many strings at once. That has been hard to do with atoms. Atoms that attract each other usually collapse into a clump. But this time, the team appears to have made many strings of different sizes at once, including some with more than six atoms.

It's tricky to get atoms to attract each other. In three dimensions, a gas made of attracting atoms tends to collapse as the atoms clump together and form molecules. That process releases energy that kicks atoms out of the experiment, so the gas quickly collapses and disappears. But when they're in a single line, the atoms behave differently.

"They are really a bit like pearls on a string, right? Like on a necklace, they cannot go past," study co-author Hanns-Christoph Nägerl, an experimental physicist at the University of Innsbruck, told Live Science. "In 3D, everything would collapse. But in 1D, it does not collapse."

To build their "necklaces," the team started with tens of thousands of cesium atoms cooled into a Bose-Einstein condensate ‪— a state of matter in which atoms chilled to near absolute zero share a single quantum state. Laser beams then divided the condensate into thousands of thin tubes, each of which held up to a few dozen atoms in a line.

At first, the atoms repelled each other. The researchers used a magnetic field to gradually turn that repulsion down to zero, and then turned it into attraction.

The team couldn't see the strings directly. Instead, they let the atoms go and measured how fast the cloud spread. When the atoms could expand only along their tubes, any strings stayed intact. When the atoms were freed in all three dimensions, the strings broke apart and released their binding energy as motion. The researchers found that the 3D clouds spread with about three times as much energy as the one-dimensional ones did.

From that difference, the team estimated how tightly the atoms had been bound. The answer pointed to strings of at least six atoms. The measurements also closely matched predictions from a theory called generalized hydrodynamics, which describes a gas like this one as a fluid made of many kinds of particles, including strings of different sizes. It also tracks how each kind flows over time rather than following every atom.

Nägerl was careful not to call this proof. "That some theory fits to your data is not a proof that something exists," he said; it's just more evidence to support it.

A short-lived state

The strings likely don't survive long. Up close, the atoms still feel the three-dimensional world, and the strings eventually decay into ordinary cesium molecules. In the coldest runs, the team lost about 40% of the atoms.

"Transiently you create these Bethe string states," Nägerl said. "But I don't think they are long-lived."

He has an idea for future experiments. Physicists recently learned to shield ultracold molecules with microwaves, which keeps the molecules from colliding at close range. Strings made from shielded molecules might last long enough to be studied directly. But Nägerl stressed that the idea is untested. "I've had nobody do a theory check on my claims now, but I think intuitively this should work," he said.

Another option is quantum gas microscopy, which images atoms one at a time and could offer more direct evidence of individual strings.

For Nägerl, Bethe strings are one step in understanding how quantum systems with many particles behave and settle down over time. His long-term goal is an experiment in which physicists control both how every particle moves and how its spin flips, letting them assemble model materials piece by piece, "like a LEGO type," he said. His team has begun the next step: using lasers to control the spins of the atoms in its one-dimensional gas. He described Bethe strings as "a little diversion." But because the strings form whenever the atoms attract, they can't be ignored.

'> Physicists froze a 'necklace' of atoms — and witnessed a quantum phenomenon predicted 100 years ago