Nuclear clocks could be the GOAT: Greatest of all timepieces. If physicists can build them, nuclear clocks would be a brand-new type. These clocks would keep time based on the physics of atoms hearts.

Some scientists believe the first of these could debut in a few years.

At the center of each atom is a nucleus. Thats where protons and neutrons are found. Clocks based on atomic nuclei could be 10 times as precise as todays most exact clocks.

Better clocks could improve technologies such as GPS navigation. But its not just about timekeeping, physicist Peter Thirolf said June 3. Nuclear clocks could allow new tests of fundamental ideas in physics. Thirolf works at Ludwig-Maximilians-Universitt Mnchen in Germany. He spoke at an online meeting of the American Physical Society.

Currently, the most precise clocks are atomic clocks. They arent based on the nucleus. They tally time using the energy jumps of electrons. Electrons in atoms can carry only certain amounts of energy, in specific energy levels. To bump electrons in an atom from one energy level to another, the clocks atoms must be hit with a laser. And the lasers light must be just right.

Explainer: How lasers make optical molasses

Light is made up of electromagnetic waves. Frequency is the rate at which those waves pass by. Only light of a certain frequency will make the electrons jump. That frequency serves as a highly precise timekeeper. Imagine using the rate at which waves wash up on a beach to keep track of time. But in this case, theyre light waves.

Protons and neutrons within an atoms nucleus also occupy energy levels. Nuclear clocks would rely on jumps of those particles instead of electrons.

Adriana Plffy is a theoretical physicist. She works at Friedrich-Alexander-Universitt Erlangen-Nrnberg in Germany. An atoms nucleus isnt as affected by stray electric or magnetic fields as the atoms electrons are. She says that suggests nuclear clocks would be more stable and more accurate.

But theres a problem. Typical lasers cant access nuclear-energy levels. For most nuclei, that would require higher energy light than normal lasers can achieve.

How excited

Luckily, theres one lone exception. A freak-of-nature thing, Marianna Safronova said in a June 2 talk at the meeting. She is a theoretical physicist at the University of Delaware in Newark.

The exception is thorium. Thorium is a metallic chemical element. There is a variety of the element known as thorium-229. It has a pair of nuclear energy levels that are close together. The energy levels are so close, in fact, that a laser might be able to set off the jump.

Scientists recently pinpointed how much energy a thorium-229 nucleus needs to make the jump. This is a crucial step toward building a thorium nuclear clock.

Thirolf and his colleagues estimated the energy by measuring electrons that the nucleus emitted when it jumped between levels. The team described its findings in Nature two years ago.Another team took a different approach. It measured the energy of other jumps the thorium nucleus can make and subtracted them. Those researchers reported their findings in Physical Review Letters last year.

Both teams agree that thorium-229s nucleus takes about 8 electron volts to jump energy levels. This energy corresponds to the edge of lasers power. That suggests lasers might be able to prompt a jump.

Detectors (shown in this false-color image made by a scanning electron microscope) measured the light emitted when thorium-229 atoms jumped between energy levels. Those measurements allowed physicists to estimate the energy of the jump needed to make a nuclear clock.Matthus Krantz

Making the jump

Physicists now are aiming to trigger that jump with lasers.

Chuankun Zhang is a physicist at JILA, a research institute in Boulder, Colo. At the meeting, Zhang reported efforts to use a frequency comb. A frequency comb is a laser with an array of light frequencies. The comb will hopefully let Zhangs team spur the nucleus to jump. It also could let the team better measure the energy needed to make the jump. If its a success, Zhang said, we can directly build a nuclear-based optical clock from that.

Thirolfs team also is working with frequency combs. His team aims to create a working nuclear clock within the next five years.

Meanwhile, Plffy is looking into using whats called an electronic bridge. Rather than using a laser to hit an atoms nucleus directly, the laser would first excite the atoms electrons. Those excited electrons would then transfer energy to the nucleus. Plffy presented this idea at the meeting.

Test of time

Nuclear clocks could let researchers devise new tests of fundamental constants of nature. A fundamental constant is a number that never changes. At least we think it doesnt ever change. Tests with nuclear clocks would help scientists figure out if the numbers are in fact constant, or if they vary over time.

Nuclear clocks could also test a foundation of Einsteins gravity theory the equivalence principle. It states that two different objects in a vacuum should fall at the same rate.

This new type of clock might even aid in the search for dark matter. Dark matter is invisible. Its made of particles that scientists have yet to detect. Physicists think these particles account for most of the universes matter. If dark matter were to interact with a nuclear clock, the interaction could tweak the clocks ticking.

Massive numbers of sharks died abruptly 19 million years ago, new data show. Fossils from sediments in the Pacific Ocean reveal that 90 percent of them vanished. And so far, scientists dont know why.

Its a great mystery, says Elizabeth Sibert. She led the new study. A paleobiologist and oceanographer, she works at Yale University. Thats in New Haven, Conn. Sharks have been around for 400 million years. And yet this event wiped out [up to] 90 percent of them.

Explainer: How a fossil forms

Sharks have suffered losses in the past. It started 250 million years ago during the Great Dying. This event marked the end of most large ocean species. Much later, about 66 million years ago, a huge asteroid fell to Earth. It killed off most dinosaurs and 30 to 40 percent of shark species. After that, sharks enjoyed about 45 million years as the oceans top predator. They even survived large climate disruptions, such as an episode about 56 million years ago when global levels of carbon dioxide spiked and temperatures soared.

The newly discovered fossils are a surprising twist in the sharks story.

Sifting sediment

Sibert sifted through fish teeth and shark scales in the sediment. She worked with Leah Rubin, a student at the College of the Atlantic in Bar Harbor, Maine. Scientists had collected that sediment during various expeditions to the North and South Pacific oceans. The project came out of a desire to better understand the natural background variability of these fossils, Sibert explains.

Sharks bodies are mostly cartilage. Unlike bone, cartilage is difficult to preserve as fossils. But sharks skin is covered in tiny scales. Each scale is about the width of a human hair follicle. These scales make for an excellent record of past shark abundance. They contain the same hard mineral as sharks teeth. Both can turn to fossils in sediments. And we will find several hundred more [scales] compared to a tooth, Sibert explains.

Fossil shark scales provided clues to the change in biodiversity after a mysterious shark die-off. Researchers sorted the scales into two main types: those with lined grooves (left) and those with geometric shapes (right). The geometric shapes all but disappeared from ocean sediments following the extinction event.E.C. Sibert and L.D. Rubin/Science 2021

What her team discovered was a surprise. From 66 million to about 19 million years ago, the ratio of fish teeth to shark scales held steady at about 5 to 1. Then the ratio took a dramatic turn: 100 fish teeth appeared for each shark scale. The team estimates this change was abrupt within 100,000 years or so.

That sudden disappearance of shark scales came at the same time as a change in the scales shapes. This provides clues about shark diversity.

Most modern sharks have lined grooves on their scales, ones that may help them swim faster. Other sharks scales have geometric shapes. The researchers looked at the change in the abundance of various scale shapes before 19 million years ago and then again afterward. This revealed a huge loss in shark diversity. It appears some seven in every 10 shark species went extinct.

And this extinction event was quite selective, notes Rubin. After the event, the geometric scales were almost gone. And that previous diversity in sharks, she adds, was never seen again. She and Sibert describe their findings June 4 in Science.

A cautionary tale

An explanation for the massive shark die-off isnt obvious, Sibert says. Nineteen million years ago is not known as a formative time in Earths history. Solving the mystery is one question she hopes to answer. She wants to understand how the varied scale shapes might relate to shark lineages. Shed also like to learn what impact the sudden loss of so many big predators might have had on other ocean dwellers.

Answers to those questions could be helpful today. Overfishing and ocean warming in the last 50 years have decreased shark populations by more than 70 percent. This loss of sharks no doubt impacts the oceans ecology.

Catherine Macdonald is a marine conservation biologist at the University of Miami in Florida. She sees the study as a cautionary tale. Our power to act to protect what remains does not include an ability to fully reverse or undo the effects of the massive environmental changes we have already made, she notes.

What happens to communities of the oceans top predators can be critical signs of those changes. Unraveling how the ocean ecosystem responded to shark losses in the past could help researchers predict what may await us now, Sibert says. The sharks are trying to tell us something, she explains, and I cant wait to find out what it is.

Ancient peoples fashioned many tools from bones. These included awls, needles and fish hooks. Two turkey leg bones with sharpened ends point to a more colorful use. Native Americans used them to make tattoos some 3,620 to 5,520 years ago. Thats the conclusion of a new study.

The sharpened turkey bones turned up at a dig site in Tennessee called Fernvale. Excavations in 1985 uncovered the bones in a mans burial pit.

These pigment-stained bones are the worlds oldest known tattooing tools, says Aaron Deter-Wolf. Hes an archaeologist with the Tennessee Division of Archaeology in Nashville. The find suggests that Native American tattoo traditions in eastern North America extend back at least 1,000 years earlier than previously thought.

The oldest known tattoos belong to tzi the Iceman. He lived around 5,250 years ago in Europe. But researchers have yet to find any of the tools used to make his tattoos.

Deter-Wolf was part of a team that studied the bones under a microscope. Tools used to create skin designs are tough to find and recognize, he says. But two turkey-leg bones showed distinctive damage on and near their tips. The pattern looks like the wear previously seen on experimental bone tattooing tools, Deter-Wolfs team says.

In that research, Christian Gates St-Pierre made tattooing tools out of deer bones. An anthropologist, he works at the University of Montreal in Quebec, Canada. Gates St-Pierre used his bone tools to tattoo lines in fresh slabs of pig skin. First, he coated the tips in a homemade ink of soot, water and wax. Then he made a series of punctures in the skin. Experimental tattooing left ink remnants several millimeters from the tools tips. The Fernvale tools showed the same pattern, only theirs are red and black pigment residues.

Other artifacts found in the same Fernvale grave suggest they may have been part of a tattoo kit. Two turkey wing bones display microscopic wear and pigment residues. Those likely resulted from applying pigment during tattooing, the scientists say. The grave also contained pigment-stained seashells. These may have held liquids into which tattooers dipped their tools.

Deter-Wolfs team described its new research in the June Journal of Archaeological Science: Reports.

The Perseverance rover has created a breath of fresh air on Mars. An experimental device on the NASA rover split carbon dioxide molecules into their component parts. This created enough breathable oxygen to sustain a person for about 10 minutes. It was also enough oxygen to make tiny amounts of rocket fuel.

The toaster-size instrument that did this is called MOXIE. The acronym stands for Mars Oxygen In-Situ Resource Utilization Experiment. Carbon dioxide, or CO2, is the primary gas in the atmosphere on Mars. MOXIEs job is to break the chemical bonds in CO2, releasing oxygen.

The device works like an electrical tree, says Michael Hecht. By that he means it breathes in CO2 and breathes out oxygen. Hecht is MOXIEs principal investigator. He works at the Massachusetts Institute of Technology, in Cambridge.

When we burn anything, gas in the car or a log in the fireplace, most of what were burning is oxygen, Hecht says. On Earth, we take all that oxygen for granted. We dont think about it. But on Mars, oxygen is largely bound up in CO2.

Lets learn about Mars

MOXIE arrived on Mars along with Perseverance this past February 18. Two months later, MOXIE warmed to about 800 Celsius (1,472 Fahrenheit). It then ran long enough to produce five grams of oxygen. Thats not enough to breathe for very long. But the main reason to make oxygen on Mars isnt for breathing, Hecht points out. Its to make fuel for the return journey to Earth.

Future astronauts will have to either bring oxygen with them or make it on Mars. A rocket powerful enough to lift a few astronauts off the Red Planets surface would need about 25 metric tons (27.5 U.S. tons) of oxygen. Thats too much to pack along.

MOXIE is a prototype for the system astronauts could one day use to make rocket fuel. When running at full power, MOXIE can make about 10 grams of oxygen per hour. Powered by Perseverance, it will run for about one Martian day at a time. Hecht notes that a scaled-up version, however, could run nonstop for the 26 months before astronauts arrive.

This diagram shows parts that go into MOXIE, an instrument designed to convert CO2 in Mars atmosphere into breathable air for future astronauts. The instrument was ferried to the Red Planet in 2020. O2 stands for oxygen, CO for carbon monoxide, CO2 for carbon dioxide and SOXE for Solid OXide Electrolyzer.NASA/JPL-Caltech

MOXIE cant run full time now because it would use too much of Perseverances power. The rover has other instruments to run as it goes about its science mission, which is to search for signs of past life on Mars. MOXIE will get a chance to run at least nine more times over the next Martian year (about two Earth years).

The success of this system could set the stage for a permanent research station on Mars, something Hecht would like to see. Thats not something I expect to see in my lifetime, he admits. Still, he says, MOXIE brings it closer by a decade.

When the COVID-19 pandemic closed gyms and put school sports on hold, many teens looked for other ways to stay active. Some took up at-home yoga or running. For high-school sophomore Michelle Hua, that wasnt enough. This 16-year-old student at Cranbrook Kingswood School in Bloomfield Hills, Mich., invented an app to track her movements. It identifies her exercises and even gives her coaching advice.

Its helped her stay active during the pandemic. Even more rewarding, that app helped her win the $75,000 George D. Yancopoulos Innovator Award, this week. Its the top prize at this years Regeneron International Science and Engineering Fair. (For more award winners, see box at bottom.) Created by Society for Science (which publishes this magazine), ISEF brought together almost 2,000 high school finalists. This year, the annual science competition was held virtually.

Michelle is a rhythmic gymnast someone who does floor exercises with props such as a hoop, ribbon or ball. The sport blends gymnastics and dance. But during COVID-19, her gym shut down. She continued to practice online at home, but Michelle wasnt satisfied. She wanted to up her training.

So the teen developed an app that tracks her movements. It even tells her whether she is performing them correctly.

Some movement-identifying apps use models of skeletons to determine movement. They analyze a video to identify body parts and identify movement based on that. But that approach is not very accurate, Michelle says. It has to know where the head, shoulders, arms, legs, feet, etc. are in each frame of the video, she notes.

Michelle decided instead to use silhouettes, outlines of whole people. With silhouettes, the program wouldnt need information about the location of body parts, she explains. It only needs to separate the shape of the human regardless of where the head, arms, [and] legs are from the background it is in.

Machine learning includes deep learning and neural nets

The gymnast designed her program using a neural-net system. This is a type of artificial intelligence program that can learn from the data on which it trains. Michelles trained hers using data from different sets of movement files. Those thousands of videos show people in all sorts of motions, from sitting to jumping and running. Her program analyzed each video, drew a silhouette and then learned what that silhouette was doing.

The program now can recognize everything from brushing your hair to chewing gum. It also can recognize exercises such as jumping jacks. But rhythmic gymnastics wasnt in any of those movement data sets on which her program trained. So the teen took videos of herself performing. I labeled my own data and trained my model with it, she says.

Michelle Hua, seen here, designed an app to help her practice rhythmic gymnastics. It analyzes her silhouette an outline of her body to assess her form.

Her new app knows what each exercising silhouette should be doing. When someone performs a jumping jack, for example, the app takes a silhouette and then might tell the user to lift her arms higher. Feedback from the app helps users correct their position to prevent any exercise-related injury, Michelle says. She hopes people will use her app to exercise more effectively. People also could use it to analyze how well they perform the physical therapy prescribed to people recovering from injuries.

In developing her project, the teen worked with Zichun Zhong. Hes a computer scientist at Wayne State University in Detroit, Mich. Together, they published results of Michelles research in the journal Computer Aided Geometric Design.  

The next step, Michelle says, is to put her app on the Apple app store. In the meantime, she notes, my younger brother and I have been using my app. It has helped us by keeping us active and exercising throughout the year.

Teens take home millions for apps, medical diagnostics and more

For her development of an exercise app, Michelle Hua today takes home the $75,000  top prize at this years Regeneron International Science and Engineering Fair. Created by Society for Science, the annual event brought together almost 2,000 high school students. They came from 64 countries, regions and territories to share their science fair projects. Due to the COVID-19 pandemic, the 2021 fair was held entirely online. The teens faced panels of scientific experts who examined their projects, and still got a chance to show their work to the public. The finalists competed over the past week for $5 million in awards.

Other major award winners, named this week, include:

Daniel Shen, 17, a junior at William G. Enloe High School in Raleigh, N.C. He won the Regeneron Young Scientist Award of $50,000. He developed an app that can respond quickly to someones facial cues.Catherine Kim, 18, a senior at Jericho High School in Jericho, N.Y. She took home the $50,000 Regeneron Young Scientist Award for developing a computer program that can help predict when medicines will interact badly with each other in someones body.John Benedict Estrada, 16, a sophomore at Clovis North High School in Fresno, Calif. For creating a robotic arm that can detect whether a plant is getting stressed by drought , he got the $50,000 Gordon E. Moore Award for Positive Outcomes for Future Generations of $50,000.Arya Tschand, 17, a senior at High Technology High School in Lincroft, N.J.  He also tackled drought, using a drone to detect dry plants and sending a signal to adjust how much water the plants received. For that, he was took the $10,000 Craig R. Barrett Award for Innovation.Neha Mani, 17, a senior at Hunter College High School in New York City. Her H. Robert Horvitz Prize for Fundamental Research, worth $10,000, rewards her development of a computer program that can distinguish between swimming and swarming bacteria to help doctors diagnose gut diseases.Franklin Wang, 17, a junior at Palo Alto Senior High School in Palo Alto, Calif. For creating a computer program that can detect speedy near-Earth asteroids, he won the $10,000 Peggy Scripps Award for Science Communication. His program has already found six new asteroids.

Along with 23 other projects from individual and teams of students, the top seven students also won first place awards of $5,000 for their research categories. Another 78 projects got second place awards of $2,000, and another 121 got third place awards of $1,000. A final 157 took home fourth place awards of $500. Even more received sponsored special awards.

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