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The ocean has now broken temperature records every day for more than a year. And so far, 2024 has continued 2023’s trend of beating previous records by wide margins. In fact, the whole planet has been hot for months, according to many different data sets.

“There’s no ambiguity about the data,” said Gavin Schmidt, a climatologist and the director of the NASA Goddard Institute for Space Studies. “So really, it’s a question of attribution.”

Understanding what specific physical processes are behind these temperature records will help scientists improve their climate models and better predict temperatures in the future.

Last month, the average global sea surface temperature reached a new monthly high of 21.07 degrees Celsius, or 69.93 degrees Fahrenheit, according to the Copernicus Climate Change Service, a research institution funded by the European Union.

“March 2024 continues the sequence of climate records toppling for both air temperature and ocean surface temperatures,” Samantha Burgess, deputy director of Copernicus, said in a statement this week.

The tropical Atlantic is abnormally warm, helping set the stage for a busy hurricane season, according to an early forecast by scientists at Colorado State University. Higher ocean temperatures provide more energy to fuel stronger storms.

Global temperatures are rising long-term because the burning of fossil fuels adds greenhouse gases, which warm the planet, to the atmosphere. So far, climate change has raised the global average temperature by about 1.2 degrees Celsius, or 2.2 degrees Fahrenheit, above the preindustrial average temperature. And because it takes more energy to heat up water than air, the oceans have absorbed the vast majority of the planet’s warming from greenhouse gases.

But the “massive, massive records” set over the past year are beyond what scientists would expect to see even considering climate change, Dr. Schmidt said.

What’s different now, compared with this time last year, is that the planet is dealing with the effects of an El Niño event that began in July. El Niño events are natural climate patterns associated with elevated temperatures.

“The temperatures that we’re seeing now, the records being broken in February and March, are actually much more in line with what we would expect,” compared with those of last year, Dr. Schmidt said. “Let’s see what happens by the summer.”

El Niño is weakening and expected to dissipate soon. What happens to global average temperatures then would help shed light on the temperatures of 2023, he said.

In addition to climate change and El Niño, there are a couple of other factors that might be contributing to these dizzying records.

One is a recent reduction in aerosol pollution from container ships traversing the ocean, following new international fuel standards that took effect in 2020. Ironically, aerosols have a cooling effect in the atmosphere, and had been helping to mask the true extent of climate change until now.

There was also the huge eruption of the underwater Hunga Tonga-Hunga Haʻapai volcano in 2022. Volcanic eruptions that happen on land send up plumes of soot and aerosols, which block sunlight and temporarily cool the atmosphere. But because this volcano was submerged under the Pacific Ocean, its eruption also sprayed millions of tons of water vapor into the upper atmosphere. Water vapor is a powerful greenhouse gas.

“It was the most explosive eruption since Krakatau, and usually the year after is when you see the impacts,” said Sean Birkel, an assistant professor at the University of Maine Climate Change Institute, who created a climate data visualization tool called Climate Reanalyzer. He suspects the warming effect of the volcanic eruption has been larger than early estimates suggested, noting that the eruption may have affected atmospheric circulation and helped amplify the El Niño that developed in 2023. But, he added, more research is needed.

Dr. Schmidt pointed out that when scientists put together their estimates so far of how much the volcanic eruption, the reduced shipping pollution, El Niño and climate change should warm the planet, the numbers don’t add up.

“There could be still something missing,” he said, like other sources of aerosol pollution having improved more than researchers know, or Earth’s climate having more internal variability than expected, or global warming amplifying the effects of El Niño.

Several groups of scientists are working to get a clearer picture, Dr. Schmidt said, and he expects results to start being published in the next few months.

Nadja Popovich contributed reporting.

After her second child was born, Chelsea Becker took an unpaid, yearlong leave from her full-time job as a flight attendant. After watching a video on TikTok, she found a side hustle: training artificial intelligence models for a website called Data Annotation Tech.

For a few hours every day, Ms. Becker, 33, who lives in Schwenksville, Pa., would sit at her laptop and interact with an A.I.-powered chatbot. For every hour of work, she was paid $20 to $40. From December to March, she made over $10,000.

The boom in A.I. technology has put a more sophisticated spin on a kind of gig work that doesn’t require leaving the house. The growth of large language models like the technology powering OpenAI’s ChatGPT has fueled the need for trainers like Ms. Becker, fluent English speakers who can produce quality writing.

It is not a secret that A.I. models learn from humans. For years, makers of A.I. systems like Google and OpenAI have relied on low-paid workers, typically contractors employed through other companies, to help computers visually identify subjects. (The New York Times has sued OpenAI and its partner, Microsoft, on claims of copyright infringement.) They might label vehicles and pedestrians for self-driving cars or identify images on photos used to train A.I. systems.

But as A.I. technology has become more sophisticated, so has the job of people who must painstakingly teach it. Yesterday’s photo tagger is today’s essay writer.

There are usually two types of work for these trainers: supervised learning, where the A.I. learns from human-generated writing, and reinforcement learning from human feedback, where the chatbot learns from how humans rate their responses.

Companies that specialize in data curation, including the San Francisco-based start-ups Scale AI and Surge AI, hire contractors and sell their training data to bigger developers. Developers of A.I. models, such as the Toronto-based start-up Cohere, also recruit in-house data annotators.

It is difficult to estimate the total number of these gig workers, researchers said. But Scale AI, which hires contractors through its subsidiaries, Remotasks and Outlier, said it was common to see tens of thousands of people working on the platform at a given time.

But as with other types of gig work, the ease of flexible hours comes with its own challenges. Some workers said they never interacted with administrators behind the recruitment sites, and others had been cut off from the work with no explanation. Researchers have also raised concerns over a lack of standards, since workers typically don’t receive training on what are considered to be appropriate chatbot answers.

To become one of these contractors, workers have to pass an assessment, which includes questions like whether a social media post should be considered hateful, and why. Another one requires a more creative approach, asking contracting prospects to write a fictional short story about a green dancing octopus, set in Sam Bankman-Fried’s FTX offices on Nov. 8, 2022. (That was the day Binance, an FTX competitor, said it would buy Mr. Bankman-Fried’s company before later quickly backing out of the deal.)

Sometimes, companies look for subject matter experts. Scale AI has posted jobs for contract writers who hold master’s or doctoral degrees in Hindi and Japanese. Outlier has job listings that mention requirements like academic degrees in math, chemistry and physics.

“What really makes the A.I. useful to its users is the human layer of data, and that really needs to be done by smart humans and skilled humans and humans with a particular degree of expertise and a creative bent,” said Willow Primack, vice president of data operations at Scale AI. “We have been focusing on contractors, particularly within North America, as a result.”

Alynzia Fenske, a self-published fiction writer, had never interacted with an A.I. chatbot before hearing a lot from fellow writers who considered A.I. a threat. So when she came across a video on TikTok about Data Annotation Tech, part of her motivation was just to learn as much about A.I. as she could and see for herself whether the fears surrounding A.I. were warranted.

“It’s giving me a whole different view of it now that I’ve been working with it,” said Ms. Fenske, 28, who lives in Oakley, Wis. “It is comforting knowing that there are human beings behind it.” Since February, she has been aiming for 15 hours of data annotation work every week so she can support herself while pursuing a writing career.

Ese Agboh, 28, a master’s student studying computer science at the University of Arkansas, was given the task of coding projects, which paid $40 to $45 an hour. She would ask the chatbot to design a motion sensor program that helps gymgoers count their repetitions, and then evaluate the computer codes written by the A.I. In another case, she would load a data set about grocery items to the program and ask the chatbot to design a monthly budget. Sometimes she would even evaluate other annotators’ codes, which experts said are used to ensure data quality.

She made $2,500. But her account was permanently suspended by the platform for violating its code of conduct. She did not receive an explanation, but she suspected that it was because she worked while in Nigeria, since the site wanted workers based in only certain countries.

That is the fundamental challenge of online gig work: It can disappear at any time. With no one available for help, frustrated contractors turned to social media, sharing their experiences on Reddit and TikTok. Jackie Mitchell, 26, gained a large following on TikTok because of her content on side hustles, including data annotation work.

“I get the appeal,” she said, referring to side hustles as an “unfortunate necessity” in this economy and “a hallmark of my generation and the generation above me.”

Public records show that Surge AI owns Data Annotation Tech. Neither the company nor its chief executive, Edwin Chen, responded to requests for comments.

It is common for companies to hire contractors through subsidiaries. They do so to protect the identity of their customers, and it helps them avoid bad press associated with working conditions for its low-paid contract workers, said James Muldoon, a University of Essex management professor whose research focuses on A.I. data work.

A majority of today’s data workers depend on wages from their gig work. Milagros Miceli, a sociologist and computer scientist researching labor conditions in data work, said that while “a lot of people are doing this for fun, because of the gamification that comes with it,” a bulk of the work is still “done by workers who actually really need the money and do this as a main income.”

Researchers are also concerned about the lack of safety standards in data labeling. Workers are sometimes asked to address sensitive issues like whether certain events or acts should be considered genocide or what gender should appear in an A.I.-generated image of a soccer team, but they are not trained on how to make that evaluation.

“It’s fundamentally not a good idea to outsource or crowdsource concerns about safety and ethics,” Professor Muldoon said. “You need to be guided by principles and values, and what your company actually decides as the right thing to do on a particular issue.”

Allies of Donald J. Trump are discussing ways to elevate third-party candidates in battleground states to divert votes away from President Biden, along with other covert tactics to diminish Democratic votes.

They plan to promote the independent candidate Robert F. Kennedy Jr. as a “champion for choice” to give voters for whom abortion is a top issue — and who also don’t like Mr. Biden — another option on the ballot, according to one person who is involved in the effort and who, like several others, spoke on the condition of anonymity to discuss the plans.

Trump allies also plan to amplify the progressive environmental records of Mr. Kennedy and the expected Green Party candidate, Jill Stein, in key states — contrasting their policies against the record-high oil production under Mr. Biden that has disappointed some climate activists.

A third parallel effort in Michigan is meant to diminish Democratic turnout in November by amplifying Muslim voters’ concerns about Mr. Biden’s support for Israel’s war in Gaza. Trump allies are discussing running ads in Dearborn, Mich., and other parts of the state with large Muslim populations that would thank Mr. Biden for standing with Israel, according to three people familiar with the effort, which is expected to be led by an outside group unaffiliated with the Trump campaign.

Many of these third-party-boosting efforts will probably be run out of dark-money entities that are loosely supportive of Mr. Trump. Both the Trump campaign and the main super PAC supporting the former president, MAGA Inc., are already aggressively framing Mr. Kennedy as a far-left radical to draw potential Democratic voters away from Mr. Biden.

Whatever the mechanism, the Trump team’s view is simple and is backed by public and private polling: The more candidates in the race, the better for Mr. Trump. Mr. Biden’s team agrees. And in a race that could be decided by tens of thousands of votes — as the last two presidential elections have been — even small shifts in the share of votes could change the result.

“There is no question that in a close presidential race, independent or minor party candidates can have a disproportionately large impact,” said Roger Stone, who is Mr. Trump’s longest-serving political adviser and who has worked on third-party campaigns, including advising Gary Johnson, the Libertarian Party’s nominee in 2012.

Republican donors are pouring funds into Mr. Kennedy’s independent bid for the presidency. He has raised substantially more from donors who previously supported Mr. Trump than he has from those who backed Mr. Biden. Some are big names in Republican politics who have so far given relatively small amounts, including $3,300 last August from Elizabeth Uihlein, whose family is among the G.O.P.’s biggest contributors.

Timothy Mellon, the largest single donor to Mr. Kennedy’s biggest super PAC, is also the largest backer of MAGA Inc. Mr. Mellon, a reclusive billionaire from one of America’s wealthiest families, has over the past year given the Kennedy super PAC $20 million and the Trump super PAC $15 million, as of the most recent disclosures that were filed in March. Another prominent Kennedy backer is Patrick Byrne, the former chief executive of Overstock.com who worked with Mr. Trump on his effort to overturn the 2020 election.

Mr. Trump himself is intensely interested in the third-party candidates, according to aides. He is eager to know what their effect is expected to be on the race and how they are polling, although his engagement beyond asking questions of those around him is unclear.

Mr. Trump has been worried about the Libertarian Party pulling conservative voters away from him in November. But Richard Grenell, who is the former acting director of national intelligence and who is expected to play a big role in any second Trump administration, has been using his connections with Libertarian activists and donors to try to persuade them to attack Mr. Biden more than Mr. Trump, according to people familiar with his efforts.

Other Trump supporters are trying to help third-party and independent candidates with the expensive and arduous process of gathering the signatures needed to get on state ballots. Scott Presler, the conservative activist whom Lara Trump said she wanted as an early hire at the Republican National Committee, publicly reached out on social media to Ms. Stein and Cornel West, a left-wing academic who is running for president as an independent, to offer his help in collecting signatures to get them on the ballot.

Mr. Presler could not be reached for comment.

The moves by Trump allies come as the Democratic Party, alarmed by the potential for third-party candidates to swing the election, has mobilized a team of lawyers to scrutinize outsider candidates, including looking into whether they’ve followed the rules to get on state ballots.

For decades, third-party candidacies have loomed large in U.S. presidential elections. The best known in modern history is Ross Perot, whose run as a billionaire populist independent in 1992 garnered 19 percent of the vote and helped Bill Clinton win with only 43 percent of the popular vote. Ralph Nader, a Green Party candidate, siphoned votes away from Vice President Al Gore in the nail-biter 2000 presidential race against George W. Bush.

And in 2016, Ms. Stein, as the Green Party candidate, gave a meaningful — and arguably election-deciding — boost to Mr. Trump by drawing progressive voters away from former Secretary of State Hillary Clinton in Pennsylvania, Michigan and Wisconsin. That year, the billionaire businessman and Home Depot co-founder Bernie Marcus, a supporter of Mr. Trump, helped fund efforts to bolster Ms. Stein.

Polling shows that third-party candidates could play an especially large role in 2024. Most Americans are unhappy with the choice between Mr. Trump and Mr. Biden. Voters are increasingly disillusioned with the two major parties, and trust in American institutions has eroded over the past 30 years. Those trends provide an opening for candidates who style themselves as anti-establishment outsiders willing to blow up the system. Mr. Trump took advantage of similar conditions in 2016.

In a Quinnipiac University poll in late March, Mr. Biden and Mr. Trump both received less than 40 percent of the vote in a hypothetical five-way race, with Mr. Kennedy getting 13 percent, Ms. Stein receiving 4 percent and Mr. West capturing 3 percent.

In the multicandidate race, Mr. Trump led by a single percentage point; Mr. Biden led Mr. Trump by three percentage points in a hypothetical head-to-head race.

“The path to victory here is clearly maximizing the reach of these left-wing alternatives,” said Stephen K. Bannon, the former White House chief strategist who also served as Mr. Trump’s campaign chairman in 2016.

“No Republican knows that oil production under Biden is higher than ever. But Jill Stein’s people do,” added Mr. Bannon. “Stein is furious about the oil drilling. The college kids are furious about it. The more exposure these guys get, the better it is for us.”

Brian Hughes, a spokesman for Mr. Trump, described Mr. Kennedy as a “leftist and liberal with a history of supporting an extreme environmental agenda.” He said more broadly of the Democratic push to challenge outsider candidates, “While Joe Biden and his allies claim to defend democracy, they are using financial and legal resources to prevent candidates access to the ballot.”

“President Trump believes any candidate who qualifies for the ballot should be allowed to make their case to America’s voters,” he added.

For months, the Trump team has been privately polling various iterations of third-party tickets in battleground states. It has concluded that candidates floated for the Green Party and No Labels, which recently abandoned its effort to field a presidential candidate, pulled substantially more votes from Mr. Biden than from Mr. Trump.

A person briefed on other polling by Trump allies said that while it varies by state, Mr. Kennedy also pulls more votes from Mr. Biden than from Mr. Trump. The person cited as an example the Trump team’s recent private polling of voters in Arizona. Mr. Trump loses Hispanic voters by a close margin in a head-to-head contest against Mr. Biden there, but he wins Hispanic voters on the full ballot in Arizona — an indication that third-party candidates draw more heavily from Mr. Biden’s core constituencies than from Mr. Trump’s.

Still, Mr. Kennedy is seen as more of a potential threat to Mr. Trump. He has spent the past few years appearing on conservative news media programs and talking about issues like his fierce opposition to the Covid-19 vaccine. Advisers to Mr. Trump say that many Republican voters don’t know anything about Mr. Kennedy’s liberal views on gun control and the environment, and the Trump team hopes to bring back some of those voters after framing Mr. Kennedy as a liberal Democrat.

Allies of Mr. Trump and Mr. Biden are in a tug of war to define Mr. Kennedy, who has far more support than any other third-party candidate.

Democratic lawyers and operatives, many of whom have privately said that neither Mr. Gore nor Mrs. Clinton had teams that took third-party candidates seriously enough, are fighting hard to keep Mr. Kennedy off the ballot. The Democratic National Committee hired Lis Smith, a veteran communications operative, and tasked her with branding Mr. Kennedy as a pro-Trump spoiler candidate.

Mr. Kennedy’s campaign and the super PACs backing him have paid an array of lawyers and consultants to secure ballot access. One of the consultants, Rita Palma, was captured in a video detailing a strategy to encourage New York voters to support Mr. Kennedy: “The Kennedy voter and the Trump voter, our mutual enemy is Biden.” Ms. Palma outlined a hypothetical scenario in which Mr. Kennedy would win enough electoral votes to prevent either Mr. Trump or Mr. Biden from winning 270 electoral votes, pushing the decision to Congress in what is known as a contingent election.

On her X account, Ms. Palma has expressed support over the years for both Mr. Kennedy and Mr. Trump. In posts first reported by CNN on Tuesday, she had endorsed Mr. Trump’s false claims that the 2020 election was stolen and described Sidney K. Powell, who has pleaded guilty to six misdemeanor counts related to Mr. Trump’s efforts to overturn his 2020 election loss in Georgia, as “My person of the decade.”

Stefanie Spear, a spokeswoman for the Kennedy campaign, described Ms. Palma as “a ballot-access consultant” for upcoming signature collection efforts in New York. Of Ms. Palma’s remarks about the hypothetical scenario, Ms. Spear said Ms. Palma’s statements “in no way reflect the strategy of the Kennedy campaign.”

Ms. Spear did not respond to requests for comment about the Trump allies’ efforts to elevate Mr. Kennedy, or to inquiries about Ms. Palma’s support for Mr. Trump’s claims about the 2020 election.

Many conservative news media personalities and influencers recently turned against Mr. Kennedy after he decided to run as an independent instead of as a Democrat and it became apparent that he could pull votes from Mr. Trump.

Still, one complication with attacking Mr. Kennedy is that Mr. Trump has made clear that he likes him.

Mr. Trump put out a statement on Truth Social, his social media platform, that called Mr. Kennedy “a radical-left Democrat,” but he has mostly laid off him otherwise. Mr. Trump has called Mr. Kennedy a “very smart person” and has even privately floated him as a potential running mate, though his advisers view that prospect as extremely unlikely.

An outside group aligned with Mr. Trump asked a question about a Trump-Kennedy ticket in a poll several weeks ago, according to a person with knowledge of the survey. The results were not particularly striking. Mr. Trump had told an ally that he believed Mr. Kennedy could help him with voters who were upset with him for his support of the Covid-19 vaccine.

“I like Trump-Kennedy. I like the way that sounds,” Mr. Trump told another ally recently. “There’s something about that that I like.”

Ruth Igielnik contributed reporting.

For the first time, the federal government is requiring municipal water systems to remove six synthetic chemicals linked to cancer and other health problems that are present in the tap water of hundreds of millions of Americans.

The extraordinary move from the Environmental Protection Agency mandates that water providers reduce perfluoroalkyl and polyfluoroalkyl substances, known collectively as PFAS, to near-zero levels. The compounds, found in everything from dental floss to firefighting foams to children’s toys, are called “forever chemicals” because they never fully degrade and can accumulate in the body and the environment.

The chemicals are so ubiquitous that they can be found in the blood of almost every person in the United States. A 2023 government study of private wells and public water systems detected PFAS chemicals in nearly half the tap water in the country.

Exposure to PFAS has been associated with metabolic disorders, decreased fertility in women, developmental delays in children and increased risk of some prostate, kidney and testicular cancers, according to the E.P.A.

Michael S. Regan, the E.P.A. administrator, called the new regulation “life changing.”

“This action will prevent thousands of deaths and reduce tens of thousands of serious illnesses,” Mr. Regan said on a call with reporters on Tuesday. He described the rule as the most significant action the federal government has ever taken to reduce PFAS exposure in drinking water.

“We are one huge step closer to finally shutting off the tap on forever chemicals once and for all,” he said.

The E.P.A. estimated it would cost water utilities about $1.5 billion annually to comply with the rule, though utilities maintain that the costs could be twice that amount and are worried about how to fund it. States and local governments have successfully sued some manufacturers of PFAS for contaminating drinking water supplies, but the settlements awarded to municipalities have been dwarfed by the costs of cleaning up the chemicals, municipal officials said.

Industry executives say taxpayers will ultimately foot the bill in the form of increased water rates.

The 2021 bipartisan infrastructure law provides $9 billion to help communities address PFAS contamination and the E.P.A. said $1 billion of that money would be set aside to help states with initial testing and treatment.

Mr. Regan is expected to formally announce the regulation on Wednesday in Fayetteville, N.C., near the site where, in 2017, a Chemours chemical plant discharged water contaminated with PFAS into the Cape Fear River, making the local drinking water unsafe.

Mr. Regan, who previously served as North Carolina’s top environmental regulator, oversaw the Cape Fear PFAS investigation at the time and forced Chemours to clean up the air, soil and water in the lower Cape Fear River basin communities.

In 2022, the E.P.A. found the chemicals could cause harm at levels “much lower than previously understood” and that almost no level of exposure was safe.

Under the new rule from the E.P.A., water utilities must monitor supplies for PFAS chemicals and would be required to notify the public and reduce contamination if levels exceeded the new standard of 4 parts per trillion for perfluoroalkyl and polyfluoroalkyl substances. Previously, the agency had advised that drinking water contain no more than 70 parts per trillion of the chemicals.

Public water systems have three years to complete their monitoring. If those samples show that levels of PFAS exceed the new E.P.A. standards, the utilities would have another two years to purchase and install equipment designed to filter out PFAS.

In a 2020 peer-reviewed study, scientists at the Environmental Working Group, a nonprofit organization, estimated that more than 200 million Americans had PFAS in their drinking water.

Public health advocates and scientists said the new regulation was overdue.

“A growing body of scientific research shows that PFAS chemicals are more harmful to human health than previously thought, and at extremely low levels,” said Anna Reade, director of PFAS advocacy at the Natural Resources Defense Council, an environmental group.

In just the past year, more than a dozen peer-reviewed studies have found evidence of additional health effects of PFAS exposure, including a delay in the onset of puberty in girls, leading to a higher incidence of breast cancer, renal disease, and thyroid disease; a decrease in bone density in teenagers, potentially leading to osteoporosis; and an increased risk of Type 2 diabetes in women.

Dr. Susan M. Pinney, the director of the Center for Environmental Genetics at the University of Cincinnati, led a longitudinal study of young girls who had been exposed to PFAS after an industrial plant in West Virginia released the chemicals into the Ohio River.

She called the number of people exposed to PFAS around the country “mind boggling.”

Robert A. Bilott, an attorney who has spent more than two decades litigating the hazardous dumping of PFAS chemicals, said he had alerted the E.P.A. to the dangerous posed by the chemicals in drinking water as early as 2001. “It has taken far too long to get to this point, but the scientific facts and truth about the health threat posed by these man-made poisons have finally prevailed,” Mr. Bilott said.

The E.P.A. calculated the health benefits of the new regulation at about $1.5 billion annually from reductions in cancer, heart attacks and strokes and birth complications.

But Republicans and industry groups, along with many mayors and county executives, said the Biden administration had created an impossible standard that would cost municipal water agencies billions of dollars.

Several questioned E.P.A.’s accounting as well as the science used to develop the new standard.

The American Water Works Association, the Association of Metropolitan Water Agencies and other groups representing water utilities estimated that the cost of monitoring and remediation of PFAS could be as much as $3.2 billion annually. The figure is based on an analysis conducted for the American Water Works Association by Black & Veatch, a firm of consulting engineers.

Communities with limited resources will be hardest hit by the new rule, they said.

“When regulations are set near zero, that is not something manufacturers or water systems can economically achieve,” Brandon Farris, the vice president of energy policy at the National Association of Manufacturers, wrote in a letter to the E.P.A. “Regulations that are not economically achievable will lead to critical substances being manufactured outside of the U.S. where environmental protections are often less stringent.”

Christina Muryn, the mayor of Findlay, Ohio, a town of about 50,000 people, said that, while clean drinking water is an imperative, the E.P.A. was requiring municipalities to meet new mandates without adequate support.

“That is very frustrating to me as a citizen, as a mayor, and as someone who is responsible for our water treatment system,” Ms. Muryn said.

Public health advocates said the costs of the new rule were outweighed by the growing body of evidence of the dangers posed by PFAS.

Widely used since the 1940s, the chemicals are useful in repelling water and oil. Nonstick pans have been most famously associated with PFAS but the chemicals can be found in water-repellent clothes and carpets, certain shampoos, cosmetics and hundreds of other household items.

The United States and Japan, faced with the challenges posed by an increasingly hostile China, are expected to further integrate their militaries and announce new agreements on technology and defense on Wednesday as President Biden hosts Prime Minister Fumio Kishida for a state visit to Washington.

The talks are part of the Biden administration’s diplomatic outreach to counter China, which includes recent war games with Seoul. On Thursday, Mr. Biden and Mr. Kishida will meet with President Ferdinand Marcos Jr. of the Philippines, another Pacific islands nation that finds itself the target of a mounting Chinese military presence in the South China Sea.

The Biden administration is signaling the importance of its relationship with Tokyo by holding an official state dinner on Wednesday evening in honor of Mr. Kishida, something reserved for America’s closest allies.

During a day of meetings, the two leaders will announce new plans designed to confront the far-reaching ambitions of China, which Mr. Biden has described as the only global rival to the United States with the “intent to reshape the international order and, increasingly, the economic, diplomatic, military and technological power to advance that objective.”

That concern comes amid hand-wringing in Washington and Tokyo over the possibility of a return to power by former President Donald J. Trump, whose unpredictable foreign policy has kept many world leaders on edge. One goal for Mr. Biden, officials said, is to create as much permanence in the Japanese relationship as possible before the election in November.

One administration official, speaking on the condition of anonymity to discuss the upcoming meeting, said there was “anxiety in capitals” around the world, including in Tokyo, about whether Mr. Trump would continue the international engagement that Mr. Biden and prior presidents have embraced. Another official said there was a real risk that Mr. Trump, if elected, could move to undo what the leaders of the two countries announce on Wednesday.

Mr. Biden and Mr. Kishida are expected to outline greater coordination and integration between the military forces of both countries, including the formation of a joint defense council that could support more defense-related exports of equipment produced in Japan. And officials said they would announce new cooperation on ventures in space and collaboration between research institutions working on A.I., semiconductors and clean energy.

“The American alliance system has helped bring peace and stability to the Indo Pacific for decades, and now we need to update and upgrade that alliance network for the modern age,” said Jake Sullivan, the White House national security adviser. “It goes way beyond security. It’s economics. It’s technology. It’s infrastructure development. And it’s diplomacy. And that’s all going to be on display in the meeting with the prime minister.”

Rahm Emanuel, the United States ambassador to Japan, called the meeting a chance for the two nations to go beyond America’s work to protect Japan and “write the first chapter of the next era” of cooperation as they work together to project power throughout the region.

That would be a more far-reaching relationship than the United States has historically had with Japan, which for decades restricted its spending on defense and its engagement around the world.

That began to change during the past several years, under Mr. Kishida, who pushed to expand defense spending and participate in global efforts like the sanctions on Russia for its invasion of Ukraine. Administration officials said Japan’s new willingness to become a full partner with the United States on the global stage has taken the alliance between the two countries to a new level.

The meeting on Thursday between Mr. Biden, Mr. Kishida and Mr. Marcos of the Philippines represents a more aggressive effort by the United States and its allies to isolate China — rather than allowing the Chinese leadership to intimidate and isolate its neighbors in the South China Sea and elsewhere.

The Thursday meeting will be the first time that the leaders of the three nations have met together, officials said.

“We’re continuing to deepen our cooperation with our closest partners to ensure what we’ve talked about many times from this podium and elsewhere: a free, open and prosperous Indo Pacific,” Mr. Sullivan told reporters during a briefing at the White House on Tuesday.

Mr. Sullivan declined to say whether Mr. Biden would raise with Mr. Kishida the issue of plans by Nippon Steel, a Japanese corporation, to acquire U.S. Steel, the struggling manufacturer based in Pittsburgh. Mr. Biden has publicly said that he will have “the backs” of union steel workers, indicating his opposition to the deal.

“You guys all know, Joe Biden,” he said. “You’ve seen Joe Biden. He’s been very clear that he’s going to stand up for American workers. He’s going to defend your interests. He’s also been very clear that he is going to make sure that the U.S.-Japan alliance is the strongest it’s ever been.”

But administration officials said later on Tuesday that they did not think the subject would come up between the two leaders on Wednesday because both men already know the position of the other.

Mr. Biden greeted Mr. Kishida on Tuesday evening for a brief arrival at the White House. Later, the two leaders and their wives went to BlackSalt, an upscale seafood restaurant in Washington, for a more casual dinner ahead of the formal events on Wednesday.

The day will begin with a welcoming ceremony on the South Lawn. It will end with a glitzy state dinner at the White House, where Mr. Biden will extend Mr. Kishida the hospitality of a meal that includes house-cured salmon and dry-aged rib-eye steak with blistered shishito pepper butter.

White House officials said the couples had exchanged a series of gifts on Tuesday evening, a diplomatic tradition for such events. The official gift from Mr. Biden and Jill Biden, the first lady, was a three-legged table that was handmade by a Japanese American-owned company in Pennsylvania.

Other gifts included a lithograph and a two-volume LP set autographed by Billy Joel and a vintage vinyl record collection. Dr. Biden gave Ms. Kishida a framed painting of the Yoshino cherry tree that the two planted on the South Lawn last spring, and a soccer ball signed by the U.S. women’s national soccer team and the Japanese women’s team.

Almost half the tap water in the United States contains PFAS, a class of chemicals linked to serious health problems. On Wednesday, the Environmental Protection Agency announced that, for the first time, municipal utilities will have to detect and remove PFAS from drinking water.

Here’s what you need to know.

What are PFAS?

In 1938 a young chemist working on refrigerants for Dupont accidentally discovered a new compound that was remarkably resistant to water and grease, a finding that would lead to the creation of the Teflon brand of nonstick cookware.

Today there are nearly 15,000 per- and polyfluoroalkyl substances, which collectively go by the acronym PFAS, according to a database maintained by the E.P.A.

The common link is that they have a special bond of carbon and fluoride atoms, making them incredibly strong and resistant to heat, water, oil and dirt. For that reason, PFAS is used for everyday items as varied as microwave popcorn bags, water-repellent clothing and stain-resistant carpets. PFAS are also in firefighting foam, cosmetics, shampoos, toys and even dental floss.

Where are PFAS?

Everywhere, including drinking water. The indestructible nature that makes PFAS useful in some products also makes them harmful. The chemicals are virtually indestructible and do not fully degrade, accumulating in the environment and the human body.

The chemicals are so ubiquitous that they can be found in the blood of almost every person in the country. One recent government study detected PFAS chemicals in nearly half of the nation’s tap water. A global study of more than 45,000 water samples around the world found that about 31 percent of tested groundwater samples that weren’t near any obvious source of contamination had PFAS levels considered harmful to human health.

What does PFAS do to the body?

According to the E.P.A., exposure to PFAS can cause damage to the liver and immune system and also has been linked to low birth weight, birth defects and developmental delays as well as increased risk of some prostate, kidney and testicular cancers. New research published in the past year found links between PFAS exposure and a delay in the onset of puberty in girls, leading to a higher incidence of breast cancer, renal disease and thyroid disease; a decrease in bone density in teenagers, potentially leading to osteoporosis; and an increased risk of Type 2 diabetes in women.

Why didn’t the E.P.A. regulate PFAS in water sooner?

Many environmental advocates argue that PFAS contamination should have been dealt with long ago.

“For generations, PFAS chemicals slid off every federal environmental law like a fried egg off a Teflon pan,” said Ken Cook, president and co-founder of the Environmental Working Group, a nonprofit advocacy group.

Activists blame chemical companies, which for decades hid evidence of the dangers of PFAS, according to lawsuits and a peer-reviewed study, published in the Annals of Global Health, of previously secret industry documents.

The new E.P.A. rule requires utilities to reduce PFAS in drinking water to near-zero levels.

How can I get rid of PFAS?

Not easily. In homes, filters attached to faucets or in pitchers generally do not remove PFAS substances. Under-sink reverse-osmosis systems have been shown to remove most but not all PFAS in studies performed by scientists at Duke University and North Carolina State University.

Municipal water systems can install one of several technologies including carbon filtration or a reverse-osmosis water filters that can reduce levels of the chemicals.

Now that limits have been set, when will PFAS disappear from tap water?

It could take years. Under the rule, a water system has three years to monitor and report its PFAS levels. Then, if the levels exceed the E.P.A.’s new standard, the utility will have another two years to purchase and install filtration technology.

But trade groups and local governments are expected to mount legal challenges against the regulation, potentially delaying it even before a court makes a final ruling. And if former President Donald J. Trump were to retake the White House in November, his administration could also reverse or weaken the rule.

Have dinosaurs evolved on other worlds? Could we spot a planet of glowing organisms? What nearby star systems are positioned to observe Earth passing in front of the sun?

These are just a few of the questions that Lisa Kaltenegger has joyfully tackled. As the founding director of the Carl Sagan Institute at Cornell University, she has pioneered interdisciplinary work on the origins of life on Earth and the hunt for signs of life, or biosignatures, elsewhere in the universe.

Dr. Kaltenegger’s new book, “Alien Earths: The New Science of Planet Hunting in the Cosmos,” to be published on April 16, chronicles her insights and adventures spanning an idyllic childhood in Austria to her Cornell office, which previously belonged to the astronomer Carl Sagan. She spoke with The New York Times about the intense public interest in aliens, the wisdom of trying to contact intelligent civilizations, and the weirdest creatures she’s grown in her lab. This conversation has been condensed and edited for clarity.

You look for real aliens in the observable universe. How much is the diversity of opinion and emotion from people around the search for extraterrestrial life top-of-mind in your research? Or are U.F.O.s and sci-fi E.T.s something you have to tune out?

For me, it’s inspirational that so many people are excited. The other part of that coin is that we are so close, because we have the James Webb Space Telescope now being able to look at these small planets that could potentially be like Earth. We don’t have to go with dubious or hard-to-interpret evidence anymore.

I wrote this book because I think a lot of people might not be so aware of where we are right now, and that they are living in this momentous time in history. We can all be a part of it.

How should people prepare for a potential detection of signs of something living in a distant planet’s atmosphere that’s not like you see in the movies, that’s maybe less satisfying?

If we were to find signs of life — any signs that we can’t explain with anything else but life — then that just means we live in a universe teeming with life, because we’re just at the verge of being able to find it. And it’s so hard, even with the best telescopes, so if we find anything, that means there’s so much more to find out there. I’ll celebrate, whatever it is.

The title “Alien Earths” refers to alien worlds, but also the past and future versions of Earth that are alien to us. What is a moment in Earth’s history that you would want to go to?

The moment and place when life started. Because it is such a mystery. You don’t need the whole planet to have conditions to get life started. It could be a niche somewhere. It could be an asteroid that hit just with the right speed and energy and mixed the chemicals on Earth up the right way. It could have been on an ice shell, or in a shallow pond.

There is an overlap between the pioneers of the search for alien civilization and the development of nuclear weapons. Do you think that kind of complicated heritage has shaped expectations about the longevity of intelligent civilizations?

Absolutely. I think in our search for life is buried the hope that if we find life everywhere, on planets older than us, that we will make it. By definition, to be able to travel the stars fast or with propulsion that can get you very far, that same technology can destroy the world you live on and everyone on it.

The question that always comes, and I think it’s a normal question, is: Will you have the wisdom to use this power for good or evil? That’s usually the story. Will you have the wisdom to survive this capability, and this technology?

There is a heated debate over whether we should be actively trying to contact alien life, or if we should just be passively looking for signs of it. Where do you come down on that question?

I was at a Vatican Observatory conference and I was actually the speaker after Stephen Hawking. Oh my god, right? Amazing. But it’s really interesting because he was one of the people who cautioned very much against this.

We are two billion years too late to worry about it. Anybody who would have looked at us for two billion years would know that there’s life on this planet. Basically, the cat’s out of the bag.

But I think it is a very valid concern in terms of social science or sociology, because we don’t want to do anything to scare people. It is worth asking the question to ourselves, too: Are we at the point, all of us, where we’d actually like to communicate with other civilizations? And what would we want to ask?

What inspired you to create the Carl Sagan Institute at Cornell?

I’m an astronomer by training, and I worked on the design of a mission to find signs of life in the universe. We were only looking at carbon copies of modern Earth. But we know that Earth has changed, so if we only look at this tiny part of the history of Earth, compared to its 4.6 billion years, we are going to miss young and future Earths.

To actually answer the question of how our planet works, you need a network of many different departments and many different ways of life. The more diverse background you can get, the more ideas you can get and the more complicated problems you can solve.

You have a lab where you’re growing microbes to inform the search for life. What’s the weirdest thing you’ve grown?

A pink fungus. You have to be very careful about fungi because they spread like crazy. This is why I’m working with microbiologists. One of my team’s microbiologists is like, “I’m not touching this and contaminating all of Cornell with pink fungus.” Imagine that.

So you had to take special precautions to make sure that this alien didn’t invade.

I just imagine a world overgrown with pink fungi.

You have published a study that simulated conditions analogous to the age of dinosaurs on other worlds. How can we specifically search for alien dinosaurs? Because I want to find alien dinosaurs.

During the age of the dinosaurs, there was more oxygen and also more methane, and that allowed for these huge creatures. At least that’s the idea, right? More oxygen can actually make creatures bigger, thus huge dinosaurs.

The fun part when I talked about this with my teammate, geologist Rebecca Payne, is that actually it could be much easier to find a dinosaur planet, to find “Jurassic World.”

Now the question is, of course: Does it have to be dinosaurs? They could be really funky different kinds of organisms that don’t look like dinosaurs.

The realities of probability tell me that dinosaurs can probably exist only once and yet my heart will not believe it.

We have 200 billion stars in our galaxy alone, and there are billions of galaxies. We have billions and billions of possibilities.

Let’s say that we are optimists and we say where life could start, it does start. That’s a hypothesis: We have no idea if that’s true. But maybe dinosaurs twice is actually an option.

More resources are needed to investigate and prosecute individuals who stole billions in pandemic relief funds, the Justice Department said in a report on Tuesday.

Federal officials said they have made “significant progress” in going after fraud, but conceded that “substantial work remains in the face of numerous challenges.” Agencies responsible for pursuing pandemic fraudsters have been restrained by budget cuts, according to the report.

The federal government, which distributed trillions in relief funds after the onset of the pandemic, has charged more than 3,500 defendants for offenses related to pandemic fraud, according to the report. That’s up from about 3,100 defendants who had been charged as of August. More than $1.4 billion in fraudulently obtained funds have been seized or forfeited.

Most cases have involved the Paycheck Protection Program, the Economic Injury Disaster Loan program and expanded unemployment benefits.

While the amount of stolen funds is unknown, the Small Business Administration’s inspector general estimated that more than $200 billion — or at least 17 percent of the roughly $1.2 trillion in pandemic loans the agency awarded — was distributed to “potentially fraudulent actors.”

The Government Accountability Office said that as much as $135 billion of the roughly $900 billion in unemployment benefits distributed between April 2020 and May 2023 were likely illegally claimed.

While most pandemic relief programs have largely ended, Justice Department officials said that state work force agencies continue to provide additional data that could be analyzed for leads. Some stolen relief funds also “remain restrained in bank accounts and need to be forfeited,” according to the report.

“The Justice Department is committed to continuing our efforts to investigate and prosecute pandemic relief fraud,” Attorney General Merrick B. Garland said.

The report also warned that cases could become harder to prosecute given the statute of limitations, which ranges from five to 10 years. The department is calling on lawmakers to pass legislation that would apply the 10-year statute to all pandemic fraud-related offenses.

“The statute of limitations must be extended and the necessary funding and data analytic tools secured for our prosecutors to recover hundreds of millions of dollars more in fraud proceeds,” Deputy Attorney General Lisa Monaco said in a statement.

White House officials have urged lawmakers to provide additional funding to help law enforcement officials prosecute cases. On Tuesday, three Democratic senators introduced legislation that would, among other things, provide $300 million to help the Justice Department beef up enforcement.

President Biden “strongly supports” the legislation, which would enact many of the pandemic-fraud proposals the president released last year, White House officials said.

After the pandemic shut down much of the economy, the federal government distributed trillions in relief funds meant to help American households and small businesses recover. But in the federal government’s haste to get money out the door, much of it was distributed with few strings attached. As a result, billions of taxpayer funds were stolen by thousands of people, ranging from sophisticated criminals to amateur fraudsters.

Federal officials have been trying to catch up to the wave of fraud for years. In addition to U.S. attorney’s offices, hundreds of people across more than 40 offices of inspectors general are working on pandemic fraud investigations, as are agents from the F.B.I., the Secret Service, the Postal Inspection Service, Homeland Security Investigations and Internal Revenue Service Criminal Investigation.

Federal prosecutors have deployed various methods to try to catch wrongdoers. At the U.S. attorney’s office in Maryland, officials have started to screen people suspected of violent crime and illegal possession of firearms for pandemic fraud. Officials at the U.S. attorney’s office in the Northern District of Mississippi have also asked county officials to review lists of individuals who received pandemic loans.

But rooting out people who exploited pandemic-relief programs has been a challenging task, given the sheer volume of fraud. Officials have conceded that some smaller-dollar thefts may never be prosecuted.

Responding to the wave of pandemic fraud has also made federal officials “keenly aware of the need for a permanent, interagency body” to combat government benefits fraud, given that some fraudsters appear to be applying the criminal skills and tools they acquired during the pandemic to continue to attack programs, according to the report.

The “bounty of spring” will be the theme of President Biden’s state dinner for Japan on Wednesday evening, an event that will feature decorations of cherry blossoms and peonies and conclude with a performance by Paul Simon.

Jill Biden, the first lady, and the White House social secretary, Carlos Elizondo, previewed the menu and the décor ahead of the dinner for Prime Minister Fumio Kishida of Japan and his wife. It will be the fifth state dinner of Mr. Biden’s term.

The guests will enter the East Wing to a wall of oversized fans that spill onto the floor, a piece of art and a metaphor with “the small end representing the beginning of life, and each pleat the many paths our lives can take,” Mr. Elizondo said.

The meal will include house-cured salmon with shiso leaf tempura (evoking a California roll) and dry-aged rib-eye beef with morel mushrooms from Oregon and shishito pepper butter. Salted caramel pistachio cake and cherry ice cream will be served for dessert.

Dr. Biden said the dinner had been designed with springtime in Washington in mind, and the decorations would evoke a garden of her favorite flowers, including sweet pea, roses and peonies.

“As guests sit among the field of flowers, glass and silk butterflies from both our countries will dance over the tables,” Dr. Biden told reporters on Tuesday.

The dinner will also spotlight Washington’s cherry trees, a present from Japan in 1912, which stand as “reminders of the gift Japan gave our nation’s capital and the bright future ahead for our partnership,” Mr. Elizondo said.

The executive chef at the White House, Cris Comerford, said the dinner included ingredients sourced from across the country.

Mr. Simon will perform after the dinner. Mr. Biden will also present Mr. Kishida with a two-volume LP set autographed by Billy Joel and a vintage vinyl record collection showcasing other American musicians, the White House announced on Tuesday.

As the evening concludes, guests will leave through a path of hydrangeas, a selection of flowers common in both the United States and Japan.

The guest list is typically released by the White House just before arrivals begin, but the Biden administration tends to invite prominent members of the visiting country, donors, administration officials and members of the Biden family.

Granting a request by federal prosecutors, the judge overseeing former President Donald J. Trump’s classified documents case ordered his lawyers on Tuesday to redact the names of about two dozen government witnesses from a public version of one of their court filings to protect them against potential threats or harassment.

In a 24-page ruling, the judge, Aileen M. Cannon, told Mr. Trump’s lawyers to refer to the witnesses in their filing with a pseudonym or a categorical description — say, John Smith or F.B.I. Agent 1 — rather than identifying them by name.

The special counsel, Jack Smith, had expressed a deep concern over witness safety, an issue that has touched on several of Mr. Trump’s criminal cases. Among the people prosecutors were seeking to protect were “career civil servants and former close advisers” to Mr. Trump, including one who had told them that he was so concerned about potential threats from “Trump world” that he refused to permit investigators to record an interview with him.

Judge Cannon’s decision, reversing her initial ruling on the matter, was noteworthy, if only for the way it hewed to standard practice. After making a series of unorthodox rulings and allowing the case to become bogged down by a logjam of unresolved legal issues, the judge has come under intense scrutiny. Each of her decisions has been studied closely by legal experts for any indication of how she plans to proceed with other matters.

But as she has in other rulings where she found in favor of Mr. Smith, Judge Cannon used her decision on Tuesday to take a shot at the special counsel, with whom she has been feuding. Although she agreed with him, she pointed out that his request to protect “all potential government witnesses without differentiation” was “sweeping in nature” and that she was “unable to locate another high-profile case” in which a judge had issued a similar decision.

The fight over the witnesses began in earnest in early February when Mr. Smith’s prosecutors asked Judge Cannon to reconsider a decision she had made allowing Mr. Trump to publicly name about 24 witnesses in court papers they had filed asking the government for additional discovery information.

The prosecutors told Judge Cannon they could not fathom why the lawyers needed to identify any of the witnesses as part of their request for more information. Mr. Trump’s legal team has argued that it has a free speech right to name the witnesses, but Mr. Smith’s deputies have scoffed at that contention.

“This is not about Donald Trump vindicating the First Amendment,” one of the prosecutors, David Harbach, said at a hearing in the case last month. “It’s just not. And we have to call it out for what it is.”

The prosecutors also told Judge Cannon that if she refused to reverse her initial ruling allowing Mr. Trump to release the names, they would challenge her decision in front of an appeals court. They were willing to directly confront her because, they said, if the witnesses were publicly identified they would be exposed to “intolerable and needless risks.”

“There is a well-documented pattern in which judges, agents, prosecutors and witnesses involved in cases involving Trump have been subject to threats, harassment and intimidation,” the prosecutors wrote.

Judges in two of the former president’s other cases — one in Washington and another in Manhattan that is set to go to trial next week — have imposed gag orders on him specifically to protect witnesses from his attacks.

When roving bands of hunter-gatherers domesticated the wolves scavenging their scraps at the end of the Pleistocene era, they set the stage for the tail-wagging, puppy-eyed canines we know and love today.

But dogs were not the only ancient canines to become companions. Archaeologists have found traces of foxes living among early communities throughout South America. This includes the nearly complete skeleton of an extinct fox discovered in northwestern Patagonia.

A team of researchers recently examined the fox’s bones, which were unearthed among the remains of dozens of hunter-gatherers. The team’s findings, published Tuesday in the journal Royal Society Open Science, posit that this fox lived alongside the humans it was buried with.

“It appears to have been intentionally buried within this human cemetery,” said Ophélie Lebrasseur, a zooarchaeologist at the University of Oxford and an author of the new study. “It’s a practice that had been suggested before, but to actually find it is a nice surprise.”

According to Dr. Lebrasseur, most archaeological traces of South American canids are usually isolated bones or teeth.

But the nearly complete skeleton of a foxlike animal was discovered when archaeologists excavated the Cañada Seca burial site in central Argentina in 1991.

The site, which was accidentally unearthed by local clay miners, also contained the bones of at least 24 human individuals and artifacts like necklace beads, lip ornaments and spear points. Analyses of the site’s human bones revealed that these people lived roughly 1,500 years ago and practiced a nomadic lifestyle.

The Cañada Seca canid skeleton was initially identified as a Lycalopex, a group of still-living foxlike canids. But closer examination of the creature’s teeth revealed that it was more likely to be the extinct Dusicyon avus, or D. avus, a medium-size fox that weighed as much as a small sheepdog and resembled a jackal. D. avus inhabited grasslands across a large swath of Patagonia from the late ice age until around 500 years ago. It was closely related to the Falkland Islands wolf, which was hunted to extinction in 1876.

Dr. Lebrasseur teamed up with Cinthia Abbona, a biologist at the Institute of Evolution, Historical Ecology and Environment in Argentina, and several other researchers to conclusively prove the identity of this skeleton. They ground down samples of the animal’s forearm and vertebrae, which they analyzed for snippets of ancient DNA.

Although the ancient DNA was degraded, the team was still able to recreate some of the fox’s genetic code. They compared it with complete genomes from domestic dogs and extant South American canids, like the closely related maned wolf. This strengthened the case that the animal buried at the Cañada Seca site was D. avus.

The genetic work also helped disprove the theory that these ancient foxes were doomed by hybridization. Some scientists speculate that when domestic dogs arrived in Patagonia around 900 years ago, they bred with foxes. This would have diluted the foxes’ gene pool and potentially created hybrid hounds capable of outcompeting purebred foxes.

But Dr. Lebrasseur and her colleagues found that the extinct foxes were most likely too genetically distinct from domesticated dogs to produce fertile offspring. Instead, the growing influence of humans on the local environment and a changing climate may have played larger roles in the species’ demise.

Another mystery was why the fox’s remains were interred at the Cañada Seca gravesite. The radiocarbon age of the fox’s bones matched the ages of the site’s human bones. The similar preservation of the two species’ bones also hinted that they were buried around the same time.

Additionally, the researchers examined isotopic signatures preserved in the fox’s teeth. While most wild canids eat almost exclusively meat, a portion of the fox’s diet was composed of maize-like plant material. This mirrors the amount of plant material that the humans buried at Cañada Seca were eating.

The new finding adds to a growing body of evidence that foxes and other native canids were important pieces of ancient South American communities. Ornaments fashioned from the teeth of foxlike culpeos adorn human remains at burial sites in Peru and Argentina. Archaeological deposits in Chile reveal that other canids were also part of the local diet.

“An animal that eats like humans and is buried like them must surely have had a close relationship with them,” said Aurora Grandal-d’Anglade, a zoo-archaeologist at the University of A Coruña in Spain, who was not involved in the study.

This relationship between fox and ancient humans may have been developed through systematic feeding. And it’s plausible that the foxes were used solely as companions, said Dr. Grandal-d’Anglade, who has studied fox remains found in Bronze Age deposits on the Iberian Peninsula.

While it appears this fox lived alongside the region’s early hunter-gatherers, Dr. Lebrasseur said she would be hesitant to snuggle up with it on the couch.

“I think the animal was likely tamed, but not something you would consider an actual pet,” she said.

Elliott Broidy, a California businessman who was once a top fund-raiser for Donald J. Trump, dropped two lawsuits on Monday against people he accused of helping to carry out a hack-and-leak operation that revealed his covert lobbying to shape the Trump administration’s foreign policy.

Mr. Broidy pleaded guilty in 2020 to conspiring to violate foreign lobbying laws on behalf of Chinese and Malaysian interests. Mr. Trump pardoned him in January 2021, just hours before leaving office.

The hack and dissemination of Mr. Broidy’s records in 2018, and the lawsuits that followed, came amid a bitter feud between Qatar and two of its regional rivals — the United Arab Emirates and Saudi Arabia — from whom Mr. Broidy was seeking lucrative defense contracts. From the beginning of the Trump administration, Mr. Broidy lobbied Mr. Trump and his aides to take a harder line against Qatar.

In the lawsuits, Mr. Broidy claimed that the Qatari government engineered the hack in an effort to neutralize his criticism of the country for financing groups linked to terrorism.

The New York Times published articles about Mr. Broidy’s activities based on material provided by an anonymous group critical of his advocacy of American foreign policies in the Middle East. Who is responsible for the hacking operation remains unclear.

One of the lawsuits was against Kevin Chalker, a former C.I.A. officer who owns a New York-based technology security firm. Mr. Broidy had alleged that Mr. Chalker and his firm, Global Risk Advisors, orchestrated the email hack on behalf of the Qataris.

When Mr. Broidy filed the lawsuit in 2019, the firm had a contract with the Qatari government that Mr. Chalker’s lawyers said focused on providing security for the 2022 World Cup, but Mr. Chalker has long denied he played any role in the email hack. In a statement on Tuesday, he said that the dismissal of the case “marks the end of nearly six years spent fighting to clear my name.”

“As I have maintained from the very outset and throughout the six years,” he said, “the accusations made about me were without merit.”

The other lawsuit, also filed in 2019, was against three lobbyists who had worked for Qatar: Nick Muzin, a Republican political operative and lobbyist; Joey Allaham, a former New York restaurant entrepreneur turned international fixer; and Gregory Howard, a former Democratic congressional aide who went on to work for public relations and lobbying firms.

The lawsuit accused the three of disseminating the hacked materials “to silence Mr. Broidy, punish and suppress his political expression, alienate him in U.S. foreign policy circles and reduce his influence on United States foreign policy — all in an effort to remove him as an obstacle to Qatar’s efforts to improve its public relations standing in the United States and abroad.”

All three denied playing any role in the hack or dissemination of the materials, as did Qatar.

Mr. Broidy last year withdrew his claims against Mr. Allaham, who admitted that he knew about the hack but asserted that he did not participate in it. He began cooperating with Mr. Broidy in his litigation.

Mr. Muzin did not respond to a request for comment.

Mr. Howard referred questions to his lawyer, who did not immediately respond to a request for comment.

Mr. Broidy’s lawyers did not make clear why they were dropping the lawsuits in their filings on Monday, and neither Mr. Broidy nor his lawyers responded to a message seeking comment.

Mr. Broidy had also sued Qatar and a former United Nations diplomat in connection with the hack, but separate federal judges ruled that the country and the diplomat had immunity from the claims.

The hacked materials showed how Mr. Broidy used his access to Mr. Trump and his administration to curry favor with foreign clients and prospective clients, including in Angola, the Republic of Congo, Malaysia, Romania, Saudi Arabia and the United Arab Emirates.

He sought to steer White House policy toward friendlier relations with the Saudis and the Emiratis — and to take a more hawkish position on their regional nemesis Qatar.

Mr. Broidy’s defense company, Circinus, won a $200 million contract from the Emirates and pursued an even larger payday from the Saudis.

In 2018, a lawyer representing Mr. Broidy wrote a letter to the Qatari ambassador in Washington saying that the legal team possessed “irrefutable forensic evidence tying Qatar to this unlawful attack on, and espionage directed against, a prominent U.S. citizen within the territory of the United States.”

If Qatar was not responsible, he wrote, “we expect your government to hold accountable the rogue actors in Qatar who have caused Mr. Broidy substantial damages.”

Seamus Hughes contributed reporting.