In 2023, a whirlwind of science headlines swept across our screens, from the find that our ancestors nearly went extinct 900,000 years ago to the discovery of a brilliant green comet in the sky. In major health news, the coronavirus public health emergency expired, and the disease took up less of our attention, though it continued to have disastrous impacts. Medical experts are anticipating updated annual vaccines will be released to continue fighting the virus as it evolves.

Also evolving rapidly this year was artificial intelligence, which found uses in everything from medicine to wildlife biology. In one innovative application, it was used to help forecast when birds took to the skies. Such an ability can help officials determine when to turn off building lights to prevent bird strikes—a conservation strategy that made national news when almost 1,000 birds died in one night after hitting a single lakeside building in Chicago.

That was a grim stat, but the year was filled with amazing news as well, including the astounding images released by the James Webb Space Telescope. In major math news, researchers found a shape with a pattern that never repeats. And in France, scientists discovered that arresting patterns left in rock are the oldest known Neanderthal cave engravings.

Unfortunately, but not unexpectedly, climate change continued to generate plenty of headlines, as the year became the hottest on record. Amid intensifying natural disasters, world leaders gathered in Dubai, United Arab Emirates, for the 28th United Nations Climate Change Conference, or COP28. While the proceedings closed with a landmark deal that made the first-ever global commitment to transition away from fossil fuels, several experts criticized the text for not going far enough.

While we were riveted by all of those stories and more, only some made our list of the biggest science events and discoveries this year. Plenty of amazing new findings surely await us in 2024, but before we cover them, here’s a look back at the moments that shaped 2023 as another major year in science.

Archaeologists find ancient Native Americans crossed back over to Asia

Grave With Bones
Researchers analyzed the bones and teeth of ten individuals who lived 7,500 to 500 years ago. Nadezhda F. Stepanova

Between 20,000 and 30,000 years ago, hunter-gatherers from eastern Eurasia likely ventured over to North America across the Bering Strait. But research this year suggests they and their descendants didn’t make a one-way trip. Several times in history, ancient Native Americans made their way back across the strait to Eurasia, according to a study published in Current Biology in January. Researchers recovered ancient DNA from ten Eurasian individuals who lived 500 to 7,500 years ago. Their analysis shows that humans with Native American lineages traveled as far away as Kamchatka and central Siberia, likely returning from North America to Asia roughly 5,000 years ago.

The find was one of many interesting discoveries related to ancient migrations and the Americas this year. In July, a study published in Proceedings of the Royal Society B described three pendants in Brazil made from sloth bones that date to between 25,000 and 27,000 years before present. That find supports the theory that humans made it to the Americas earlier than previously thought. (For many decades, researchers thought humans traveled from Russia to Alaska roughly 15,000 years ago.) And in an October study published in Science, an analysis of evidence found near fossilized footprints in New Mexico suggests that the imprints date to 23,000 years ago, which also supports the idea of an earlier migration of humans to North America. While the timeline of migrations to the Americas—and back—continues to be debated, many sites that will offer more clues await discovery and analysis. —Joe Spring

Artificial intelligence yields scientific breakthroughs as experts call for caution

2023 was a “breakout year” for artificial intelligence. Following the release of OpenAI’s ChatGPT at the end of 2022, machine learning has increasingly been in the public eye. A.I. made its way into courtrooms, music and art this year, raising a slew of ethical concerns. In the realm of science, the cutting-edge technology is paving the path toward new discoveries and more advanced processing of data.

Several groups of researchers experimented with having A.I. algorithms generate words, images and even music based on people’s brain scans—a technique that, down the line, could help stroke patients and paralyzed people to communicate by thinking. Machine learning has helped in conservation, such as by tracking migrating birds—the A.I.-powered tool BirdCast can alert people to an incoming wave of migrants, which may help prevent disease, inform Lights Out programs to reduce window strikes, and tip off birders about flocks in their area. Scientists are also developing A.I. tools that can identify species based only on a photograph, distinguish between similar-looking mushrooms or pinpoint a bird species from its song. And, inspired by the way ChatGPT follows patterns in language to generate words, researchers have experimented with translating whale sounds using A.I.

At the same time, experts warned this year of the need to regulate the rapidly advancing technology. Geoffrey Hinton, a machine learning pioneer widely called the “Godfather of A.I.,” quit his part-time job with Google in May so that he could speak more freely about his unease regarding A.I.’s future. Experts have raised concerns that A.I. could spread misinformation, manipulate humans and alter the job market if it isn’t controlled. But innovation continues, and it seems likely that researchers will increasingly use A.I. to attempt breakthroughs in many fields. —Carlyn Kranking

NASA retrieves asteroid bits to shine light on Earth’s origins

Sample of Bennu Asteroid
The asteroid sample that is now on display at the National Museum of Natural History. NASA Johnson Space Center

On September 24, 8.8 ounces of rock and dust collected from an asteroid named Bennu landed in the Utah desert. The astronomical delivery was the result of a more than seven-year NASA mission in which the agency’s OSIRIS-REx probe journeyed 1.2 billion miles to the asteroid to retrieve the sample. The 4.5-billion-year-old Bennu existed before Earth did, so it could hold clues about how our planet formed and which building blocks of life meteorites delivered here long ago.

Initial analysis revealed evidence of water and a high carbon content on Bennu. While the OSIRIS-REx spacecraft is already off to visit another asteroid, researchers on Earth will study the Bennu sample for two years and set aside some of the rock for later examination. And while much of the rock will be analyzed behind closed doors, a 0.3-inch, 0.005-ounce sample is on display at the Smithsonian’s National Museum of Natural History, so you can get a glimpse of an object that is truly far-out. —J.S.

The Titan submersible imploded while searching for a shipwreck

The world watched in June after OceanGate’s Titan submersible went quiet during a dive to the Titanic. The craft and its five passengers descended toward the famous wreck on Sunday, June 18, at 8 a.m., but it lost contact with its base ship, the Polar Prince, around 10:45 a.m. At 5:40 p.m., roughly three hours after the sub was supposed to breach the surface, officials notified the Coast Guard the craft was overdue. Airplanes and a Bahamian research vessel with remote-operated robots helped scour an area twice the size of Connecticut. Numerous television stations and news outlets covered the search as fears mounted that the crew was running out of oxygen. And on Thursday morning, the Coast Guard found debris consistent with a catastrophic implosion of the submersible.

Onboard was Stockton Rush, the CEO and co-founder of OceanGate, who considered himself a maverick and breaker of rules. He had gone forward with that dive and others despite safety concerns. Two former employees had raised issues about the craft’s hull, and more than three dozen experts warned that catastrophic problems could occur due to company’s experimental approach. Though many in the public waited to hear news about the sub after it went missing, experts expected the worst. And while the actual scientific benefits of Titan’s dive were likely minimal, the sub’s tragic end shed a light on the value of the time and effort that goes into scientific exploration of the deep sea. Scientists who dive to the ocean’s depths for serious study go down in crafts that have undergone rigorous testing. Because of that, nearly 50 years had passed since a fatal accident on such a submersible. That all changed with a company that dove despite multiple warnings. —J.S.

Wildfires burned through Canada and Hawaii

Lahaina After the Wildfire
The town of Lahaina lay in ruins after a deadly wildfire swept through it. Kyodo News via Getty Images

Devastating wildfires dominated the news again in 2023. Blazes set a record in Canada, scorching more than 45 million acres by October. The country’s previous annual record, standing since 1989, was less than half that, at 19 million acres burned. As climate change causes higher temperatures, Canada’s fire season has become longer by about two weeks, and larger fires have grown more common. Hundreds of such “megafires,” covering 39 square miles (10,000 hectares) or more, incinerated our northern neighbor this year. Many had massive clouds above them, like those usually seen above volcanoes, that created lightning and high winds. And Canada’s major burns affected others around the world: During June, parts of the United States’ Midwest and Northeast regions registered the globe’s worst air quality, and pollution reached as far as Spain, Britain and Norway.

Canada’s catastrophic fires weren’t alone. On August 8, a devastating blaze swept across the Hawaiian island of Maui and engulfed the city of Lahaina, killing at least 100 people. The death toll is the highest caused by a wildfire in the U.S. in more than a century, and thousands of residents lost their homes. On the islands, some seasons are hotter and drier due to climate change, allowing wildfires to spread at increasing speeds. Climate change is altering many other such areas around the planet, threatening to make what was once considered extreme fire become more and more the norm. —J.S.

UFOs break into government discourse and spark conspiracy theories

In 2023, alien conspiracies and UFO speculation riddled social media, but at the same time, some of the stigma around researching unidentified anomalous phenomena, or UAP, began to break down.

For starters, the U.S. Office of the Director of National Intelligence released a report in January that announced more than 350 sightings of UAPs had been logged by the government since March 2021. Nearly half of these were described as “balloon or balloon-like entities”—a subject that took center stage the following month, when the U.S. government shot down what was suspected to be a Chinese high-altitude spy balloon off the coast of South Carolina. The incident demonstrated how identifying UAPs has implications for national security.

Then, at a House of Representatives hearing in July, former U.S. intelligence officer David Grusch alleged in a testimony under oath that the federal government is covering up evidence of crashed vehicles and biological material believed to be of “non-human” origin. In September, alien discourse appeared in legislative chambers once more, when a self-proclaimed UFO expert unveiled what he claimed were the bodies of extraterrestrials in front of Mexico’s Congress. Scientists balked at the suggestion, pointing to several previous alien theories from the speaker that had been debunked. Ultimately, anyone looking for confirmation of aliens on Earth didn’t get it this year—after a 12-month study, NASA released a report on UFOs in September, stating its scientists found “no conclusive evidence” that the mysterious phenomena have an extraterrestrial origin. —C.K.

Orcas break rudders and sink ships in the Strait of Gibraltar

Orcas gained attention this year after ramming boats. Francois Gohier / VW Pics / Universal Images Group via Getty Images

Maybe it’s a form of play. Maybe it’s a passing fad. Or maybe, as internet onlookers from around the world have facetiously suggested, it’s a full-fledged, female-led orca uprising, planned as retribution for humanity’s presence in the high seas. (Scientists aren’t on board with that last one.) Whatever the reason, orcas off the coasts of Portugal and Spain have been ramming into and breaking rudders off ships in the Strait of Gibraltar. Since 2020, more than 500 interactions with contact between orcas and boats have occurred, and four of these incidents—with two this year—resulted in a vessel sinking, most recently in November.

In May, a scientist suggested the curious behavior started after one orca had a negative experience with a boat, and that it spread as juveniles watched her break rudders. This led people to cheer for the orcas on social media. But in an open letter in August, a group of 35 scientists warned against attributing human traits to the animals. Doing so, they wrote, could lead mariners to take aggressive action against the orcas, which belong to a critically endangered population of fewer than 50 individuals. Indeed, some sailors have thrown firecrackers into the water in an attempt to keep orcas away.

Amid all the mystery around the behavior, one thing seems clear—the orcas do not appear to have malicious intentions. “Quite frankly, if they really wanted to take revenge, they would,” biopsychologist Lori Marino told ABC News in July. —C.K.

Covid-19 entered a new phase

Though, to many people, Covid-19 faded into the background this year, the disease remains a problem as the vaccine response has lagged. On May 11, the Biden administration allowed the coronavirus public health emergency to expire, leading the virus to be treated like other respiratory ailments. (Insurance providers were no longer required to provide free Covid-19 tests, and some medicines, such as Paxlovid, were no longer guaranteed to be free.)

A new variant, XBB, became dominant in early 2023, and in September the Food and Drug Administration authorized an XBB booster, which also works for other Omicron variants. But by the end of October, the Department of Health and Human Services said only about 4.5 percent of the population had received the shots, despite the fact that the Centers for Disease Control and Prevention (CDC) recommended the updated dose for everyone six months or older. The reception was lower than the previous year’s booster, which more than 23 million Americans had received after a similar timespan. The lackluster uptake continued a trend of declining response to boosters. As of December, roughly 70 percent of the population had the primary series of the vaccine, while less than 20 percent had received a bivalent booster. While the virus was not spreading at the rate of previous years, as of early December, more than 5,000 people were hospitalized on an average day and more than 1,200 deaths were occurring each week. Much of the population, including people who are over 65, pregnant or immunocompromised, are still vulnerable to the disease.

And some folks continue to deal with the aftereffects of the virus: This June, roughly 6 percent of the population was suffering from long Covid, according to the CDC. And of those, more than one in four experienced significant limitations in their ability to perform normal daily activities. As the disease continues to evolve, the Biden administration says citizens should expect to have a shot available each fall, like the schedule for flu vaccines. But whether people will actually be receptive to that shot remains to be seen, following the decline in this year’s response. —J.S.

A teenage tyrannosaur fossil preserves what young dinosaurs ate

Gorgosaurus consumes its prey. Julius Csotonyi © Royal Tyrrell Museum of Paleontology

Adult tyrannosaurs—large, bipedal carnivores of the Late Cretaceous—were fearsome predators in the prehistoric landscape. With their bone-crushing bite force, the fully grown dinosaurs could bring down massive plant-eaters. Young tyrannosaurs, on the other hand, might have had more limited pickings with their slender frames, narrow skulls and blade-like teeth. At least, that’s what paleontologists suspected. But they didn’t have proof until this year, when researchers reported a fascinating discovery: a “teenage” tyrannosaur, with its final meals preserved intact.

The astounding fossil of Gorgosaurus, uncovered in 2009 and described in Science Advances in December, provides the first direct evidence of shifts in a tyrannosaur’s diet from adolescence to adulthood. Within the carnivore’s stomach were four legs—two pairs—from small, bird-like dinosaurs called Citipes elegans. Each pair of legs shows different levels of digestion, suggesting they represent the young reptile’s last two meals, consumed hours or days apart. The juvenile tyrannosaur, which was between 5 and 7 years old, likely had to chase down these fast, turkey-sized prey. The findings suggest that young, agile Gorgosaurus survived on bits of baby dinosaurs until they grew big enough to take down titans. —C.K.

2023 becomes the hottest year on record

Worldwide, 2023 started out warm. April and May ranked among the hottest months of their kind in written history. But when summer arrived in the Northern Hemisphere, records fell left and right. Heat waves gripped regions of the United States and Southern Europe. American municipalities set more than 1,000 daily temperature records in June and July, and residents of Phoenix sweltered through an unprecedented 31-day stretch of at least 110 degree Fahrenheit temperatures. Even heat-adapted saguaro cactuses fell over and died. Oceans warmed to levels unparalleled in the nearly 45-year record, with one thermometer in the Florida Keys measuring “hot tub” heat levels at 101.1 degrees Fahrenheit in July.

The life-threatening heat was wide-reaching: On one weekend day in August, more than 111 million Americans in the South and Southwest were under heat warnings. Month after month—first June, then July, August, September, October and November—clocked in as the hottest months of their kind ever documented. With both climate change and the arrival of the heat- and moisture-bringing El Niño weather pattern, 2023 is now guaranteed to become the hottest year on record. But since, historically, El Niño’s most extreme heat arrives during its second year, some scientists warn that 2024 might be even more chart-topping. —C.K.

Caption of Top Image: Illustration by Emily Lankiewicz / Clockwise from upper left: Unsplash, Mojahid Mottakin; Nadezhda F. Stepanova; Francois Gohier / VW Pics / Universal Images Group via Getty Images; NASA Johnson Space Center; Unsplash, Jarosław Kwoczała; Unsplash, Fusion Medical Animation; Ocean Gate / Handout / Anadolu Agency via Getty Images; Unsplash, Bruce Warrington; Unsplash, Benjamin Lizardo; Julius Csotonyi © Royal Tyrrell Museum of Paleontology

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