Aaron P. Bernstein/Reuters

Senator Al Franken (D) of Minnesota arrives at the US Capitol with his wife Franni Bryson to announce his resignation in the wake of numerous allegations of sexual misconduct.

Sen. Al Franken (D) of Minnesota’s decision to resign his seat – announced Thursday from the floor of a somber, almost funereal Senate chamber – reflects just how quickly, and comprehensively, his party is moving to stake out an uncompromising position on the issue of sexual misconduct.

Calling himself a champion of women, Senator Franken said flatly that some of the allegations against him “are simply not true” and that others he “remembers very differently.” He insisted that as a senator, he has done nothing to bring dishonor on the institution.

Yet Franken acceded to demands that he step down. In the end, he may not have had much choice: After yet another accusation against him emerged this week, many of his Senate colleagues, led by a group of female lawmakers, came forward publicly to say “enough is enough.”

Franken’s decision follows that of Rep. John Conyers (D) of Michigan, who announced his retirement on Tuesday, in the wake of a series of sexual harassment allegations involving staffers.

The twin announcements put Democrats on the moral high ground – albeit one with twists and turns. The party has shown itself willing to sacrifice two iconic political figures as the country grapples with a systemic scourge. And, as Democrats are well aware, it puts them in stark contrast to Republicans, who have been divided over how to respond to sexual misconduct allegations against their Senate candidate in Alabama, Roy Moore, and whose president also has been accused of harassment.

As Franken put it in a parting shot: “There is some irony in the fact that I am leaving, while a man who has bragged on tape about his history of sexual assault sits in the Oval Office, and a man who has repeatedly preyed on young girls campaigns for the Senate.”

Courage and consequences

“It shows some courage by Democrats to step up and do this, especially Democratic women who have been leading this charge,” says Emily Parcell, a Democratic consultant in Iowa who worked on the presidential campaigns of Hillary Clinton and Barack Obama. “It demonstrates an obvious commitment to doing what’s right, over putting party first.”

But Democrats also run the risk of being accused of ignoring due process, of summarily pushing out members before an investigation could run its course. Speaking of the drumbeat of calls for Franken to resign, conservative Fox News host Laura Ingraham warned her viewers of a “lynch mob” that “could be coming for your husband, your brother, your son, and yes, even your president.”

Other Republicans came to Franken's defense, characterizing him as a scapegoat of sorts. Ari Fleischer, the former press secretary for President George W. Bush, tweeted:

Slightly higher marks for Democrats

Still, right now, the politics look better for Democrats on this. A Quinnipiac poll taken before this week’s resignation announcements found that neither party got particularly high marks on sexual harassment, though Democrats rated higher with 28 percent approving of their handling of the issue, and just 21 percent approving of Republicans’ handling of it. That was in contrast to the media, whose approach to sexual harassment won approval from 48 percent of Americans – a reflection, perhaps, of the high-profile firings of television journalists such as Matt Lauer and Charlie Rose.

Sen. Jeff Flake (R) of Arizona – the lone Republican to watch Franken’s speech and then shake his hand afterward – said he has been “concerned for a while” that Republicans are ceding the moral high ground.

“With Roy Moore, certainly,” he told reporters on Wednesday, though he’s grateful that almost all of his Republican colleagues in the Senate have said the controversial judge should step aside, even as President Trump threw his support behind Moore. Also, the Republican National Committee reversed course this week and announced it would support the candidate financially. Several women have come forward to say that Moore behaved inappropriately with them when they were teenagers and he was in his 30s.

Notably, Senator Flake wrote a $100 check – and put a picture of it on Twitter – in support of Moore’s Democratic opponent, Doug Jones.

According to a Democratic Senate aide, Franken’s resignation puts Democrats in a far stronger moral and messaging position if Moore is elected to the Senate. While Senate majority leader Mitch McConnell has said Moore would “immediately” face an investigation by the Senate Ethics Committee if he were elected, that investigation could take months or even years. Indeed, Franken’s declared readiness to comply with an ethics investigation was seen by some as an effort to buy time.

It’s also significant that Sen. Kirsten Gillibrand – whose name is often mentioned as a potential challenger to President Trump in 2020 – led the charge against Franken in the Senate, becoming the first of Franken’s colleagues to call publicly for his resignation. The Democrat from New York has long been at the forefront of the sexual harassment issue, starting with the military. Senator Gillibrand also drew attention last month for an interview in which she said that, in hindsight, President Bill Clinton ought to have resigned from the White House over the Monica Lewinsky affair.

“She’s getting in front of this issue,” the Senate aide said.

Women lawmakers in both the House and Senate, including Republican Rep. Barbara Comstock of Virginia, have in recent weeks successfully pushed for legislation to require mandatory harassment training in Congress. They also want to overhaul the process of reporting allegations, which they describe as onerous and tilted against victims. The lawmakers are responding to a wave of complaints of rampant harassment in Congress.

What they are demanding is zero tolerance for sexual harassment at the Capitol.

“We need to draw a line in the sand and say none of it is okay, none of it is acceptable,” Gillibrand said at a news conference on Wednesday. “We as elected leaders should absolutely be held to a higher standard, not a lower standard, and we should fundamentally be valuing women. That is where this debate has to go.”

Who's next? 

But not all misconduct is alike, and that has some on the Hill now wondering whether it is OK for a male senator and a female staffer to be alone in the same room together, or what grounds might be for the next resignation. Staffers are talking among themselves about who might be next – with some speculating that many more shoes will drop. As Senator Flake told reporters, “I don’t think every allegation is alike,” though he thinks Franken did the right thing by resigning.

“We don’t want to over-correct in the other direction,” says Ms. Parcell, the Democratic consultant.

A greater test of moral courage for Democrats might be if the party were willing to call for the resignation of a colleague in a state where a successor would be appointed by a Republican governor.

In Minnesota, a Democrat will make the appointment until the next election – though as Franken himself pointed out, he won his first election by only 312 votes. His seat will almost certainly be in play in a special election next fall to finish out his term until 2020. In Michigan, the governor – a Republican – must call an election to fill a vacancy, and Representative Conyers’ seat representing portions of Detroit is safely Democratic.

When it comes to sexual harassment, “If you are willing to put partisanship aside in one case, I would expect you would put partisanship aside in every case,” Parcell said, even if it’s painful.

The sexual harassment issue is part of a larger picture and won’t be the only ground that elections are fought on, says Democratic pollster Mark Mellman. Still, his advice to future candidates is to “think long and hard if you have any indiscretions in your past because chances are they are going to come out.”

Staff writer David Sloan contributed to this report.

For the past five years, Ms. Peng has worked as a cleaner in a Beijing office block. It was a tiring, low-paying job – the kind that is easily overlooked but essential in cities around the world.

Beijing is no different. Over the past four decades, millions of migrants have flocked here from poor rural China in the hope of finding a better life. They have built the city’s gleaming new skyscrapers, they have cared for its children, and they have sold and delivered its groceries, among other services.

While the municipal government has hardly welcomed the newcomers – denying them basic rights such as free public education and health care – it has long accepted them as essential to Beijing’s transformation into a modern capital. They number close to eight million, nearly a third of the city’s population.

Now, suddenly, the authorities have turned on migrant workers like Ms. Peng, who gave only her surname, forcing them out of the city by demolishing their homes. Over the past two weeks tens of thousands – possibly hundreds of thousands – of people have been evicted.

Most of the victims seem resigned; there is little they can do to resist the government. “If they don’t let us live here, we have no choice but to go home,” Peng said sadly last Friday, rummaging through her belongings in a cluttered apartment on the northeastern edge of the city.

Her heating and electricity had been cut off ten days earlier, in mid-winter subzero temperatures. On Sunday, she and her husband bowed to the inevitable and flew to their home province of Sichuan, where they still have a plot of land. They have no plans to return.

Peng’s neighbors appeared to have taken similar decisions. Many of the shops and apartments near her home were already deserted.

Peng’s abrupt departure, and that of untold thousands of other migrants, raises questions about what Beijing will look like – and how well it will function – when they are gone. The government says it needs to restrict the city’s population to ease the strain on public resources such as water and roads. But some experts warn that driving out migrants threatens the city’s overall growth and productivity.

“Every city has its own ecology, just like in nature,” says Guo Yuhua, a sociology professor at Tsinghua University in Beijing. “If you kick out a part of the population you disrupt the social ecology of the city.”

Jason Lee/Reuters

Migrant workers leave with their belongings after they were required to move out of the area due to a citywide fire safety inspection prompted by a deadly fire in an apartment block, at Xinjiancun in Daxing district, in Beijing, China November 25, 2017.

“With these sorts of shocks to the system, we see just how important and integral these migrant workers are to the economy,” says Keegan Elmer, a researcher at China Labour Bulletin, a labor rights group based in Hong Kong. “A lot of middle-class Beijingers are starting to finally feel and understand just how important these people are to their nice, comfortable lives.”

Evicted for their own good?

Beijing authorities say migrants are being removed for their own safety. Last month a fire in a crowded housing complex on the outskirts of the city killed 19 people. Seventeen of them were from other parts of China.

When Peng first heard about the fire, she knew her days in the city were probably numbered. Sure enough, three days later, an eviction notice appeared outside her apartment building, its wording oddly cheery: “Hope everyone finds a place to live and moves as soon as possible. Hope you can find a warm and comfortable house! Thank you for your cooperation!”

Peng and other migrants say fire safety is a thinly veiled pretext for the evictions. The government had clearly planned the mass eviction campaign; it was launched just two days after the fire. And while officials say they are now targeting more than 25,000 safety hazards across the city, the authorities have been shutting down shops and restaurants owned by migrants for more than a year.

Last January the city approved a plan to demolish more than 430 million square feet of illegal buildings by the end of this year, and its goal of limiting Beijing’s population to 23 million residents by 2020 is well known.

“Beijing is kicking out migrant workers everywhere,” says Gao Yanhua, a migrant from Hebei province who works with her repair-man husband. “It’s getting harder and harder to live here.” She says she expects her own apartment in the southern district of Daxing to be torn down soon

The recent evictions have been especially brutal. Whole families have been given very little notice to vacate their homes in freezing weather, often finding their water and electricity cut off, before the backhoes arrive.

The campaign prompted 100 public intellectuals to sign a petition deploring the evictions as a violation of human rights, but that has made no difference. Nor has widespread anger online, where citizens have criticized the government for denying migrants, who provide crucial services in Beijing, the same status as the city’s residents enjoy. 

If they don't do the work, who will?

Meanwhile, analysts have raised concerns about the effect the evictions will have on Beijing’s economy. Bloomberg Economics warns in a report published on Monday that the recent evictions could shrink the city’s workforce, hamper potential growth, and lead to inflation.

Among Beijing’s official resident population, the number of working age adults is dwindling. The city needs working-age migrants to help fill the low-paying jobs that keep the city running. If their numbers shrink, prices of goods and services will likely rise.

Li Yunfei, for example, who manages a hotpot restaurant, says it’s getting harder to find new employees. His costs have increased 40 percent this year as the supply of cheap labor dries up.

“You can’t divide people in a city into ‘high-end’ and ‘low end’ populations and move out all the ‘low-end’ population,” says economist Hu Xingdou, using a derogatory term that the government has used to describe poor migrant workers. “If you move them out, no one will work in the service industry. The economy will stall and the city will become more and more unlivable.”

Beijing’s burgeoning e-commerce sector has been hit especially hard by the eviction drive. Fewer migrants means fewer drivers to provide the almost instant delivery of everything from coffee to couches that middle-class clients of online shopping sites have come to expect in the capital.

Ma Yanlong, a courier for ZTO, says his workload has increased by 20 percent in recent days.

But Mr. Ma, like many of his fellow couriers, isn’t sure how much longer he’ll be able to stay in Beijing. He too has found a notice posted outside his apartment, giving him until Dec. 10 to move out. Ma hopes he can find a new place to live before then. After all, he says, Beijing is where the jobs are.

Xie Yujuan contributed reporting to this article.

John Macdougall/Reuters

US President Donald Trump and British Prime Minister Theresa May wait at the start of a session of a Group of 20 meeting in Hamburg, Germany, on July 7.

When a report came out Sunday claiming that President Trump's first official visit to Britain had finally been scheduled for late February, it didn't take long for the backlash to come.

Within minutes of The Sunday Times article putting a date – Feb. 26 to 27 – to the controversial visit, activists vowed to organize the biggest protest in British history to greet Mr. Trump. Thousands of Britons – many still angry about Trump’s retweeting last week of anti-Muslim videos published by Britain First, an extreme far-right group – have already pledged to attend, despite the lack of official confirmation of the date.

The controversy is hardly the first since Trump took office to have rocked the so-called “special relationship” between Britain and the United States. Things seemed to start well; British Prime Minister Theresa May was the first world leader to visit the president in January. But since then, the Trump administration has tested relations with one of Washington's oldest allies in a series of missteps, outbursts, and spats – leading to the president's deep unpopularity today among Britons.

Experts say the special relationship is likely to endure due to its importance to both countries. But the strains upon on it will likely keep Mrs. May in particular in a bind, as she is forced to maintain US ties even as doing so erodes the support she receives from the anti-Trump public at home.

“These flashpoints where [Trump] does something completely out of step with Western values are likely to continue,” says Brian Klaas, a fellow in comparative politics at the London School of Economics. “And Theresa May will have to face them and the public’s reaction again and again for the next few years, if they both remain in office.”

A tested relationship

Trump and his administration have, wittingly or not, triggered multiple diplomatic flare-ups with Britain. In March, then-Press Secretary Sean Spicer cited at a White House briefing an unsubstantiated allegation that British intelligence services had tapped Trump Tower on behalf of President Obama during the presidential election. The accusation infuriated British officials, and drew a rare public comment from Britain's GCHQ intelligence service, which called the claim “utterly ridiculous.”

In the aftermath of the June 2017 terrorist attack on London Bridge, Trump publicly berated London Mayor Sadiq Khan on Twitter over Mr. Khan's response to the city’s terror attacks. Trump's tweets, which took Khan's response out of context and were made during a period when most world leaders were offering statements of support to London, angered many Britons for both their apparent attempt at point-scoring and their ill-considered timing.

There have also been points of tension. Canadian aeronautics manufacturer and major Belfast employer Bombardier, following a complaint by US company Boeing, was hit by the US with a 300 percent import tax. May personally lobbied Trump to step in, as the decision put more than 1,000 jobs in Belfast at risk, but her efforts failed, earning her criticism from the Labour party for her “lack of negotiating skills.” Trump’s resistance to certifying the Iran nuclear deal also irked Britain. Most recently, Trump's Britain First retweets brought condemnations from across British society, including from May herself.

And US-UK relations would “no doubt” be even worse, says Leslie Vinjamuri, an associate fellow in the US and the Americas program at international affairs think tank Chatham House, if not for Brexit, which has both put her in a weak position on the international stage, and also given her plenty of distraction. “Theresa May has been constrained because her primary focus has been negotiating with the European Union on some really tough issues,” says Dr. Vinjamuri.

But Trump's impact on the relationship goes much deeper than these public spats, says Tim Oliver, an associate at foreign policy think tank LSE IDEAS at the London School of Economics. As well as ensuring the continued commitment of the US to defend Britain and Europe, the relationship was built on the pursuit of common goals in terms of economics, politics, and security on a broader global level. These broad goals, sometimes referred to as a liberal internationalist agenda, include the commitment to free trade, for example.

“When Mr. Trump got elected, he was very hostile to NATO, very suspicious of American commitments, and very protectionist,” Dr. Oliver says. “From the start, therefore, he seemed to challenge the very strategic rationale for Britain's close relationship with the United States.”

Constraints for May

But on the fundamental ways the two countries cooperate – nuclear weapons, intelligence, and special forces – they remain largely on the same page. Oliver says: “These core shared interests have traditionally been protected by the vagaries and fallings out between prime ministers and presidents as both sides benefit so much from it.”

He adds: “Mr. Trump, however, has been pushing this to its limit.”

And it poses a particular challenge to May, as one leader of the side currently more likely to try to maintain the relationship. In the British press and in Parliament, May has been accused of accepting the president’s behavior purely for a trade deal with Britain. The public is much less conciliatory: The Pew Research Center found that 75 percent of the Britons had “no confidence” in Trump to do the right thing when it comes to world affairs. An earlier poll by Opinium found that half of the British public think he is “dangerous.”

May is in a “lose-lose situation” Vinjamuri says, and Trump's upcoming visit could be a real test. She says: “If she calls [the visit] off over the controversy, then she has laid down a very clear marker with her most important ally. But if she goes ahead she is going to have a lot of unrest on the streets at a time when she is in a very weak position.”

Dr. Klaas agrees. “Both parties know a state visit is going to spark immense protests, and that could be very damaging and embarrassing to Mr. Trump because he cares about perception and appearances. But that encapsulates the problem because Mrs. May is dealing with the fact she has to have a close relationship with a partner that the British public does not want her to have a close relationship with.”

But other factors are involved in sustaining the relationship. “Donald Trump is not the same as the US government,” Klaas says. “He is in charge of one branch of three and he is also out of step with his statements with the overwhelming majority of the government establishment, both in terms of foreign policy and basic values.”

“You can’t ignore the president,” Klaas adds, “but overall he won’t destroy the special relationship.”

Johnny Andrews /The Seattle Times/AP/File

Plans to build a new, $210 million juvenile-justice center and lockup in Seattle are met with opposition by protesters in January 2017. For the past 20 years, it’s been up to county prosecutors across the state to decide which 16- and 17-year-olds accused of committing certain violent crimes are 'auto declined' to adult, or superior, court and which ones are prosecuted in the juvenile system.

Massachusetts could be the first state to view 18-year-olds as juveniles in the criminal justice system.

A sweeping criminal justice reform package that would, among other things, raise the age of criminal majority to 19 – meaning that 18-year-olds would be treated as juveniles for most crimes – recently passed in the state Senate.

The House version of the bill left the age of criminal majority at 18 – indicating that not everyone in the state legislature is on board with raising the age. A committee is now tasked with reconciling the two bills before sending the end product to the governor.

If the age of criminal majority at 19 is signed into law, it would mark the highest age of juvenile jurisdiction in the United States. 

The proposal follows on the heels of widespread reform across the country to raise the age to 18. Ten years ago, 13 states – including Massachusetts – didn't consider 17-year-olds to be juveniles when they were arrested. Today, five states are holdouts, four of which are currently considering legislation to change that.

Prompted by a growing body of research on adolescent mental development, some studies suggest including teens in the juvenile system lowers recidivism rates. The push to raise the age also signifies a larger shift in the way society defines adulthood, observers say. Legal experts in Massachusetts and elsewhere see raising the age to 19 or higher – as has been suggested in Connecticut – as a natural next phase of the movement.

“The argument seems to be just about settled, when it comes to public safety and justice, that older adolescents – 17-year-olds, 16-year-olds – belong in the juvenile justice system,” says Joshua Rovner, juvenile justice advocacy associate at The Sentencing Project in Washington, D.C. “So I think it's pretty clear that the next step in this is to continue expanding the juvenile justice system.” 

Reform in the juvenile justice system is happening across the board in the United States, from adjusted forms of sentencing – which Vermont is in the process of rolling out – to rethinking how those sentenced are incarcerated. This comes at a time when the number of young people being jailed is at its lowest level in two decades, thanks to a drop crime rates and reform efforts. 

But despite the momentum, changing the age of criminal majority may not be a simple shift. New philosophical questions and concerns arise when 18-year-olds – who are considered mature enough to vote and join the military – are included in the juvenile system. And on a practical level, experts say, shifting a large cohort of young adults from the adult to juvenile systems may not be possible for all states.

Shifting perceptions of adulthood

Accepting 18-year-olds in the juvenile system may hinge in part on society's shifting definitions of adulthood. 

For generations, being 18 meant the start of adulthood in more ways than just the ability to cast a vote or buy a lottery ticket, observers point out. In 1960, nearly half of all young people ages 18-24 were married, says Vincent Schiraldi, senior research scientist and adjunct professor at the Columbia School of Social Work in New York. Today, as college enrollment rates rise and more Americans delay marriage, it's rare to find a recent high school graduate who's married with a mortgage and a full-time job. 

For men in particular, marriage and steady, gainful employment – two steps that now typically come later in life – have proven to be important deterrents from crime.

Taking on serious adult roles helps to occupy young men's time, making them less likely to commit criminal acts, says Professor Schiraldi. “They haven’t really taken on those fully adult roles at 18 in the United States like they had in previous generations, but the law really hasn’t changed to reflect that.” 

Differences between the juvenile and adult justice systems vary from state to state, but across the board, juvenile systems tend to have a greater focus on rehabilitation. Naoka Carey, executive director for the Boston-based Citizens for Juvenile Justice, points to increased opportunities for education and interaction with family as key factors that differentiate the Massachusetts juvenile and adult systems. 

Such opportunities can mean the difference between moving forward toward a productive life and falling back into old criminal patterns, Carey and other advocates of raising the age say. A report from the Centers for Disease Control and Prevention found that teens transferred into the adult justice system were more likely to be re-arrested than those who remained in the juvenile system. 

Findings like these, along with a large body of research suggesting that adolescents are still developing mentally into their 20s, have contributed to successful reform efforts to include 16- and 17-year-olds in the juvenile system. In 2017, it's largely accepted by the public that, with the exception of those accused of extremely violent crimes, minors should be tried as juveniles, observers say. 

Arguments against the increase

Add 18-year-olds into the equation, however, and fresh arguments surface. If an 18-year-old is adult enough to vote or join the military, critics of the proposal posit, they should be adult enough to take full responsibility for their actions.

Carey counters that not all privileges of adulthood – such as drinking alcohol or renting a car – are available to 18-year-olds, and that “nothing about your 18th birthday gives you great insight or ability.” Many 18-year-olds are still in high school, she and other supporters of the bill say, and can still benefit from the academic opportunities and parental support offered by the juvenile system. 

“Treating people as juvenile until their 19th birthday will result in many 18-year-olds being treated as their classmates are,” writes Democratic state Sen. William Brownsberger, sponsor of the Massachusetts bill, in an email to the Monitor. 

Some experts also dispute the effectiveness of some recent laws raising the age to 18, a measure that may vary depending on individual states' policies and one's definition of success. A study of the Illinois justice system by researchers Charles Loeffler and Ben Grunwald found no significant statistical change in recidivism rates since the state changed its laws in 2010 to try 17-year-olds with misdemeanors in juvenile courts. (Illinois began including 17-year-olds charged with felonies in the juvenile system in 2014.)

“Some people look at that and say that’s clear evidence that it worked, there was no great increase in crime or reoffending among juveniles affected by the policy, so this is great,” says Dr. Loeffler, an assistant professor of criminology at the University of Pennsylvania. “Other people look at that and say, 'Well, I thought we were supposed to see a crime reduction,' ... and they're both sort of right.” 

More options could arise

Mr. Rovner of The Sentencing Project predicts that, if passed and signed into law, the Massachusetts reforms could serve as a model for the rest of the country.

“I think that, as happened with raising the age to 18, state legislatures and policymakers will look at the experience of leading states as Massachusetts to see how it plays out,” he says. 

Others are skeptical. Michele Deitch, an attorney specializing in juvenile justice policy and senior lecturer at the University of Texas at Austin, says that while she expects a few states might move in the direction of raising the age to 19 or higher, she would be surprised if such reforms become the new norm. Moving large swaths of 18-year-olds into the juvenile justice system is likely to raise costs, she adds. 

More likely, Ms. Deitch predicts, is the development of a intermediate justice system for 18- to 25-year-olds. For example, she says, states may keep offenders in this age range in the adult system, but introduce new sentencing laws for this age group and provide separate housing in more rehabilitation-oriented facilities. 

A slightly different approach to reform may be rethinking not just the age at which young people move into the adult system, but the adult system itself, suggests Loeffler. While considering raise-the-age laws, he says, advocates and policymakers might ask which valuable aspects of the juvenile system offenders miss out on once they turn 18 and whether it would be possible to improve upon the adult system in similar ways. 

“Another way of thinking about the problem is, ‘Well, what is it we’d like these individuals to receive that they don’t currently receive in terms of either treatment or other services?’ ” he says, "and figure out how to get them those services where they are.” 

Deep in the dense jungle of Mexico, pools of water that dot the thick vegetation may resemble the shallow ponds found in forests all over the world. But these seemingly boring puddles are actually deep sinkholes, or cenotes as they are known locally, and form portals to another world.

Thomas Iliffe and David Brankovits aren’t hesitant to enter these watery portals. Clad in wet suits and headlamps, and lugging multiple oxygen tanks and sample jars, the two biologists and their colleagues have plunged into the murky cenote waters many times.

As they dive down, sometimes as deep as 80 feet below the surface, the water becomes so crystal clear it almost seems as if they could remove their respirators and take a breath – despite being sometimes as far as 1,000 feet from breathable air.

At times they have to wriggle through tight spots in the rock to enter roomy caverns or dodge stalactites and stalagmites, relics of a time before this subterranean world was flooded. At more than 160 miles long, the Ox Bel Ha cave system that lies beneath the Yucatán Peninsula is the longest explored underwater cave system in the world.

“To be down there is otherworldly, to put it mildly,” says Dr. Iliffe of Texas A&M University, who has been diving in caves like these for more than 30 years.

As the divers glide through this pitch-black watery world, their electric lamps occasionally alight on a tiny flash of white in the water. This is what they came to study: life.

In this seemingly inhospitable environment, a menagerie of microbes and tiny crustaceans, just millimeters in length, share a home with fish that grow up to 6 or 8 inches long. All the animals are blind and many are white or partially transparent, as they have no adaptive need for sight or flashy colors in the pitch dark.

Biologists have puzzled over the presence of this extensive biodiversity in such a dark, forbidding place. What could there possibly be down there to sustain such an ecosystem? Dr. Brankovits has part of the answer for the Ox Bel Ha system, in a paper published last week in the journal Nature Communications. His research found evidence of a methane-based food chain with a surprising link to the above-ground biosphere in this cave system.

But understanding the food web for all kinds of caves across the globe could hold much broader implications. Studying life that survives in these seemingly inhospitable subterranean worlds expands our understanding of what life is capable of – and where else we might find it.

Courtesy of Joerg Hess

Biologist and diver Tom Iliffe disappears through a small hole in the cave wall that leads to a new section of the Yucatán cave system.

An otherworldly window

“[Caves] are kind of like a whole other planet underneath our feet,” says Penelope “Penny” Boston, director of NASA’s Astrobiology Institute, who was not part of this study. “These worlds, these little planet-lets under our feet, have the potential for being proxies for radically different planetary environments.”

One thing that makes caves otherworldly is their isolation. “In the subsurface, it’s all geologically partitioned,” explains Dr. Boston, who is also a cave biologist. These underground caverns and crevices are enclosed in rock. But caves aren’t always completely sealed off from the surface world. Water can seep through pores in the rock, and some caves have passageways that connect them to the surface. Still, life dwelling in these subterranean caves is relatively isolated from the biological processes occurring above on the surface of the Earth. And that includes the process that we often think of as the biological linchpin of the food chain: photosynthesis.

Without any sunlight reaching deep into these caves, there can be no photosynthetic organisms. Instead, scientists have found chemical-eating microbes at the base of the food chain. In some of the dry cave systems that Boston studies, like the Cueva de Villa Luz in Tabasco, Mexico, bacteria munch on hydrogen sulfide gas – which is highly poisonous to humans – then everything else lives off that bacteria either directly or indirectly. That gas is produced by geological systems, so the food web in that cave is quite isolated from the biology at the surface.

But Brankovits, now a researcher for Woods Hole Oceanographic Institution and the US Geological Survey, found that the same is not entirely true for the water-filled Ox Bel Ha cave system.

Courtesy of Sergio Benitez

This cave-adapted shrimp, Typhlatya pearsei, lives in the Ox Bel Ha cave system in the Yucatan Peninsula and was one of the subjects of a study investigating the food web in that underground system. It can grow to just over half an inch long.

During his PhD studies at Texas A&M University at Galveston with Iliffe as his adviser, Brankovits studied the diet of a few cave-adapted shrimp, all members of the genus Typhlatya, as a window into the food chain in the cave system. He and his colleagues found that much of the shrimp’s diet came from bacteria that was munching on methane.

But, Brankovits says, that methane isn’t geologically produced. Instead, it originated on the surface. The process goes something like this: Plants in the jungle die, falling to the forest floor to decay. In the rot process, the plants are broken down into smaller and smaller parts, largely by microbes. Then, water dissolves this organic matter down even farther, washing it through the permeable rock and further breaking it down into tiny molecules, including methane. That methane and other dissolved organic material then seeps through the limestone into the caves below, where more microbes eat it.

So, despite being deep underground, the Ox Bel Ha shrimp are still benefiting from sunlight and photosynthesis.

But Iliffe suggests other mechanisms might be at play, too – ones that might not be connected to the surface biosphere.

The Ox Bel Ha cave system’s very waters might reveal such mechanisms.

Because the caves are near the coast, ocean water has seeped into them. Freshwater seeps in from above, too. But the two don’t mix much. Instead, a layer of fresh, slightly brackish, water sits atop a denser layer of saltwater.

There is a sharp divide between the two waters, called a halocline. Swimming in the freshwater and looking down at the saltwater, Brankovits describes, “it’s almost like you are swimming above a lake in a cave.”

Some of the cave-adapted organisms don’t cross this boundary, which makes it a site for much ongoing and future research. And learning more about what happens at and around that boundary might reveal mechanisms sustaining the cave life that have no connection to surface photosynthesis.

Courtesy of Brankovits et al.

Caves within a karst subterranean estuary are filled with separated fresh, brackish, and saline waters. Within the subterranean estuary, methane (CH4) and other forms of dissolved organic carbon (DOC) created during the decomposition of soil from the overlying tropical forest sustain a complex cave-adapted ecosystem.

Stretching the bounds of life

“If we actually want to better understand how life can exist in different environments, then caves provide a good natural laboratory for that,” Brankovits says. Between intriguing formations like these stratified waters, the absence of sunlight, limited organic matter, limited oxygen, biology’s use of inorganic sources to sustain itself, and the isolation of caves even from each other, each cave a biologist studies could provide a unique new model of an ecosystem.

“Caves are really beautiful windows into this underground world,” says Jennifer Macalady, a geomicrobiologist at Pennsylvania State University, who was not part of the Ox Bel Ha research team. There are crevices and pore spaces all over the world that probably contain similar biological processes, she explains, but caves are “human-sized voids” where scientists can actually explore and conduct experiments.

And exploring these caverns could help expand our knowledge of the organisms that we share this planet with. Estimates vary dramatically, but microbiologists say there are probably some 1 trillion different species of microbes on Earth. And about 99.999 percent of those microscopic organisms have yet to be discovered by scientists, so studying life in caves could help close that knowledge gap.

Scientists aren’t just discovering new microbe species in caves, though. The crustaceans and fish are also unique, cave-adapted species. Many of them only reside in one cave system in the world, making them critically endangered because pollution or another sort of destruction of that one cave could drive all the species within it to extinction, Iliffe says. (So, please don’t try to eat the fish, he adds with a laugh.)

Biologists look for undiscovered organisms all over the world, particularly in extreme environments. “It helps us understand what the boundaries of Earth-like life really are,” Dr. Macalady explains.

Caves are just one example of these extreme environments where life can be found, but with their variety of seemingly-inhospitable environments, caves attracted the attention of astrobiologists, like Boston.

In searching for life on another planet (or moon), it’s important to establish the broadest boundaries of where life might exist and not make assumptions based on what conditions are comfortable for humans. In caves here on Earth, for example, Boston has found a diverse array of organisms while wearing a gas mask and covering every inch of her skin to protect from conditions that could kill a human.

“These environments seem extreme to us,” Boston says, “but for them, it’s home sweet home.”

AP Photo

Israeli police officers try to remove a Palestinian flag from Palestinian women protesting outside the Damascus Gate in Jerusalem's Old City Dec. 7. Clashes between hundreds of Palestinian protesters and Israeli troops erupted across the West Bank on Thursday while demonstrators in Gaza burned posters of President Donald Trump and Israeli Prime Minister Benjamin Netanyahu, as well as Israeli and U.S. flags.

One popular tool for peacemaking over the past century has been the use of independent mediators to resolve conflicts. Their work has grown because the costs of modern warfare have become too high. In the Middle East, the United States often played this role of third-party facilitator. It created bridges between Israel and its adversaries by building up trust, empathy, patience, and openness. Has that evenhanded approach by the US now ended with President Trump’s decision to move the American embassy from Tel Aviv to Jerusalem?

A key critic of Mr. Trump’s decision believes so. Palestinian Authority President Mahmoud Abbas said the US has made “a declaration of withdrawal” as a balanced mediator. In Jerusalem, meanwhile, the city’s authorities tried to make clear that the US now stands solidly behind Israel. They beamed a joint image of the US and Israeli flags on the Old City’s walls.

This perception that the US has stepped back from its historical role of diplomatic neutrality – often dubbed “shuttle diplomacy” – may open an opportunity for others. In past decades, Norway and other European powers have achieved some success in Middle East mediation. The United Nations is on constant standby as a dialogue facilitator. Egypt, having made its peace with Israel in the 1970s, has a record of being an arbiter.

The region is so conflict-ridden with religious and ethnic disputes – and ever more deadly weapons – that this relatively modern concept of mediation needs to be constantly reinforced and its benefits made clear. Compromises are often not seen as onerous when a mediator can point to common interests that put a different light on core differences.

Peacebuilding comes in many forms, of course, such as the work of local activists who create reconciliation between small groups of people. This is called “peacebuilding from below.” On a larger scale, would-be mediators must be vigilant to detect whether a conflict is ripe for reconciliation and then seek an opening for dialogue. 

If a peace deal is not even conceivable – as now seems the case between Israelis and Palestinians – then the wisest tactic is to keep both sides talking. This is low-level engagement that at least holds off a cycle of violence. For decades, that tactic was the fallback position of the US in the Middle East.

Following Trump’s decision, many Palestinians have called for a resumption of violence. Israeli troops are already confronting Palestinian protesters. An outside party, if not the US, must soon intervene and offer confidential negotiations that lead to quiet persuasion. Mediators help stretch the thinking of antagonists to discover different ways of identifying themselves as well as discovering different futures other than maintaining an adversarial relationship. Jaw-jaw is better than war-war, but it often takes a go-between to get that going.