BALTIMORE — For centuries, clashes between science and religion have made waves within society at large and in the academic world. You probably haven’t heard very much, though, about similar clashes between science and history.

Yet scientists and historians have fundamentally different perspectives on history, especially when it’s the history of science. Scientists tend to celebrate the discoveries of the past that built the knowledge of the present. Historians argue that the scientists of the past should be viewed through the lens of their own time, not evaluated on the relevance of their work to today’s textbooks.

One prominent physicist who objects to the historians’ modus operandi is Nobel laureate Steven Weinberg of the University of Texas at Austin. His 2015 book To Understand the World unabashedly analyzes the scientific past in the light of the present. “I knew from the beginning that I was being naughty,” Weinberg said March 14 at a meeting in Baltimore of the American Physical Society.

In technical terms, Weinberg was engaging in “Whig” history (an allusion to criticisms of British historical accounts involving a prominent political party). Whig historians write (or rewrite) history as a story validating the chain of events that created present-day circumstances. Most historians argue that such an approach distorts the record of the past. Much of what happened in the past had little to do with how things are now, and historical actors certainly had motives other than creating a future they couldn’t even have imagined. “We don’t want to read history only from the winners’ point of view,” commented historian David Wootton, also speaking at the physical society meeting.

But limiting historical accounts to evaluating the past “on its own terms,” without admitting current knowledge into evidence, misses much of the story, Weinberg asserts.

And as Weinberg points out, it’s often hard to understand the past on its own terms anyway. Especially when studying early Greek philosophers, it’s impossible to know very much about the conditions under which they worked and the influences that shaped their thought. Even many of their own writings are missing or fragmentary.

“Our knowledge of present science provides a contrast to the attitudes and methods of the past, attitudes and methods that often obstructed progress,” Weinberg said.
Of course, the notion of progress itself is one of those concepts that some historians deny; it implies a value judgment that things now are somehow better than they used to be. But in science, progress of some sort is very hard to deny. Wootton, the historian, agrees with Weinberg on that point. Wootton believes many historians go too far in denying the notion of progress in many fields, with science being the most prominent example.

“The progress has been real and needs to be studied and explained,” Wootton said. “Understanding the past in its own terms is not enough” — a point he also makes in his recent book The Invention of Science.

Other historians view their task more narrowly, insisting that scientists of the past should be studied in light of their efforts to solve the problems posed in their own day within their own worldview. But that is not the story of science’s past that interests Weinberg.

He agrees that early scientists dealt with different problems. “Scientists of the past were not just like scientists of today who didn’t know as much we know. They had completely different ideas of what there was to know, or how you go about learning it,” he said. “But the point of scientific work is not to solve the problems that happen to be fashionable in your own day — it is to learn about the world.”

So that makes the stories that historians like to tell irrelevant (to him).

“It is the history of the change in the attitudes of what was there to know, and how do you find it out, that seems to me the most interesting … story.” That’s the story, Weinberg believes, that helps in understanding how science has succeeded and perhaps even helps identify present-day mistakes.

“The real story is the progress of science from an earlier day when the most intelligent and well-informed people in the world did not know how to address the mysteries of nature,” he said. “We’re certainly not finished, and we’re undoubtedly still making mistakes. But we have amassed a large amount of reliable knowledge, and more important we have developed techniques for deciding when knowledge really is knowledge or just a mistake. It is a great story. It’s not at an end. But we have learned some things, and if we don’t use the things that we have learned, then the story we tell has no point.”

As Superstorm Sandy threatened the East Coast of the United States in fall of 2012, people stocked up on bread and batteries. They boarded their windows. And they tweeted. During the height of the storm and its impact, between October 26 and November 10, people sent more than 20 million hurricane-related tweets.

Now, scientists have taken almost 10 million of those tweets and used them to show where Sandy hit. They also found that tweets about the storm’s damage were associated with how much financial support ended up getting handed around. The results show that social media can be used to track the damage from natural disasters. And they suggest that eventually, these social networks might be able to contribute to disaster response.

These days, if an earthquake happens miles away, you may read about it on Twitter before you even feel the tremor. In some cases, earthquake information actually travels faster via tweet than from scientific instruments. In 2009, the Defense Advanced Research Project Agency held the DARPA Network Challenge — a contest designed to see how social media and the Internet could be used to solve time-sensitive problems. Manuel Cebrian, a computational social scientist now based at the Commonwealth Scientific and Industrial Research Organization in Clayton, Australia, won that challenge with his colleagues by using social media to hunt down 10 red weather balloons released across the United States.

Since then, Cebrian and his colleagues have been applying social networks to other, more disastrous events.

First, they tried to see if they could predict outbreaks of contagious disease. But soon, they turned their minds to large-scale disasters. Hurricane Sandy was the perfect target. It was a disaster big enough that everyone cared about it. The storm, which made landfall in New Jersey on October 29, 2012, killed at least 147 people. It also caused $50 billion in damages and left 8.5 million people without power.

The disaster was large — and came at a time when Twitter had become “a pervasive technology that everyone was using,” Cebrian explains. This made Sandy a good storm to test the powers of Twitter.

A storm of social media
The scientists analyzed 9.7 million tweets from 2.2 million users posted between October 15 and November 12, 2012. They restricted their search to tweets where they could determine the location of the user. Cebrian and his group compared “hurricane-related” messages using keywords such as “Frankenstorm,” “Sandy,” and “hurricane” to tweets that contained vague, non-Sandy-related terms such as “weather.”

By comparing Twitter use in 50 cities in the United States, the researchers found that the closer the city was to the hurricane’s path, the more storm-related tweets were sent in the period immediately before, during and after Sandy’s big day, the researchers report March 11 in Science Advances.

Showing that tweets could track a storm’s path was “the main goal,” Cebrian explains, but then the team moved on to a more difficult question: Whether tweets were also associated with material storm damage. “It was kind of a long shot for us,” Cebrian admits. But Superstorm Sandy again had good data to offer. Using the publicly available data from the Federal Emergency Management Agency and private insurance companies on how much money was spent on storm recovery, the scientists were able to show the volume of tweets about Sandy in New Jersey and New York was associated with how much money people in the area received for damages. Cebrian and his group were even able to apply their methods to 12 other natural disasters, including the South Napa earthquake and the Oso mudslide, and see similar results.

“We were surprised there was any correlation at all” between tweet volume and damage, Cebrian notes. “These are two very different processes.” On one hand, you have Twitter, something many people do when distracted, “you are looking at a million things and talking to your mom and then you tweet,” Cebrian says. “On the other hand, to know how much money goes into your house…they have to take pictures and assessment and get the numbers approved. You are looking at a well calibrated process.”

The study is much larger than many previous studies of social media and disaster, says Julia Skinner, who studies social media, political unrest and natural disasters at Kennesaw State University in Georgia. “It combines a lot of different ways that researchers have considered social media and disasters into one approach,” she explains.

The study also showed that people retweet less in the path of the hurricane, which suggests there is “more new information coming from areas close to the hurricane,” says James Bagrow, who studies social media and disaster response at the University of Vermont in Burlington. “This isn’t ‘cowboy science,’” he says. “They did a good job of supporting the decisions they made along the way.”

To tweet or not to tweet
Though Cebrian has done several analyses of Twitter, he himself doesn’t tweet. “I’ve never used Twitter,” he admits. “I’m not very good with this technology.”

But it has still proven to be a rich resource to mine. “Twitter is this weird mix of a social network where people check on their friends, but also an information network where agencies try to reach out to people,” Cebrian says.

Twitter is also useful because it’s public, Skinner explains. “Even if you don’t have an account, you can see what people are saying about a disasters, while on a platform like Facebook or Snapchat, people’s privacy settings might prevent you from seeing what they have to say.”

But not everyone tweets, and that means the results will end up skewed. “Twitter has great penetration in America,” Cebrian notes. But other countries might not be so well represented. “We can’t claim universality,” he says. It also depends on the natural disaster. People may be very excited about issues that are not yet local. “Twitter can be very good if you want to raise awareness, but it might not be a good tool today to see where Zika is traveling,” Cebrian notes.

So far, the associations between tweet and destruction was still only moderate. “This is the beginning,” Cebrian notes. He hopes that down the line, companies such as Twitter and Google might want to help do further research. But he also says, in the end, the emergency aid groups have many methods, and “this is only another tool.”

For Wisconsin’s snowshoe hares, climate change now ranks as an even bigger menace than the bulldozing, paving and other destructive things people have done to northern forests.

Habitat loss as humans reshape landscapes has loomed for decades as the main conservation problem for a lot of wildlife. It’s still important, says climate change ecologist Benjamin Zuckerberg of the University of Wisconsin‒Madison. But along the southern boundary of the snowshoe hares’ range, climate change bringing skimpy snow covers has surpassed direct habitat loss as a threat, Zuckerberg and his colleagues say March 30 in Proceedings of the Royal Society B.
North America’s Lepus americanus hares may be especially sensitive to climate change. “Almost everything about them screams adaptation to seasons of extensive snow cover,” says study coauthor Jonathan Pauli, also at Wisconsin‒Madison. The hares have outsized snowshoe feet, thick fur and an annual molt from brown to snow-white. Getting out of sync with the snow turns camouflage into a come-on for predators (SN Online: 1/26/16). In bad years, “there’s a lot of white hares on brown backgrounds,” Pauli says.

To see how the hares have fared, the researchers looked for signs of the animals at 199 sites during the winters of 2012‒2013 and 2013‒2014. Many of these locations were mentioned in a rather anecdotal 1945 study and in a more systematic one in 1979 to 1980. Satellite images showed not much change in the overall amount of hare-suitable forest since the 1980s, but snow cover averages have declined. When researchers put all their information into a computer simulation, the climate-related changes — particularly the length of the snow-cover season — did a better job of explaining the ups and downs of hare populations than just the forest changes did.
Snow cover has powerful effects on hares. For each 7.41 days that snow blankets the landscape, snowshoe hare populations become four times as likely to survive, the researchers found.

If the hares dwindle from a place, the loss may ripple through the ecosystem. “Snowshoe hares are central, really central, to prey species,” Pauli says. Lynx, great horned owls, coyotes and many more species dine on them. And regardless of any ecosystem role, hares are remarkable creatures in their own right. “It’s hard for me, a person living in Wisconsin, to imagine these northern conifer forests without snowshoe hares,” Pauli says.
To prevent such a loss, reducing greenhouse gases is important, but so is creating “climate-resilient landscapes,” Zuckerberg says. For snowshoe hares, that landscape might bristle and tangle with abundant, thick young growth, full of hiding places for too conspicuous, out-of-season-sync hares, he suggests.

White furry animals may not be the only ones that will have to cope with a shift in the balance of threats. “In a number of cold-associated butterflies, and also birds, it is becoming clear that climate change is beginning to surpass land use as the primary driver of extinction at the trailing edges of the species’ range,” says ecologist Tom Oliver of the University of Reading in England. And the threats of climate change and land-use upsets can intensify each other. “We appear to be entering a worrying time,” Oliver says.

NEW YORK — Sometimes forgetting can be harder than remembering. When people forced themselves to forget a recently seen image, select brain activity was higher than when they tried to remember that image.

Forgetting is often a passive process, one in which the memory slips out of the brain, Tracy Wang of the University of Texas at Austin said April 2 at the annual meeting of the Cognitive Neuroscience Society. But in some cases, forgetting can be deliberate.
Twenty adults saw images of faces, scenes and objects while an fMRI scanner recorded their brains’ reactions to the images. If instructed to forget the preceding image, people were less likely to remember that image later. Researchers used the scan data to build a computer model that could infer how strongly the brain responds to each particular kind of image. In the ventral temporal cortex, a part of the brain above the ear, brain patterns elicited by a particular image were stronger when a participant was told to forget the sight than when instructed to remember it.

Of course, everyone knows that it’s easy to forget something without even trying. But these results show that intentional forgetting isn’t a passive process — the brain has to actively work to wipe out a memory on purpose.

Tadpoles don’t cry to get their way. But some of them sure can beg.

Each bout of hungry-baby drama among mimic poison frogs (Ranitomeya imitator) occupies both parents for hours. The tadpoles get so crazy-frantic that researchers wanted to know whether the begging is an honest call for help or a histrionic scam.

Frogs can lay globs of eggs by the thousands and leave them to fend for themselves. But the two-to three-egg clutches of mimic poison frogs (the only known monogamous frogs) get coddled, says Kyle Summers of East Carolina University in Greenville, N.C. Dad repeatedly checks in, sitting on the eggs and shedding some paternal pee if they’re drying out.
When the eggs hatch, dad gives each tadpole a piggyback ride to its own private pool. To find a little rainfall cupped between a leaf and stem, he’ll haul youngsters four meters or so. “A bit of a hike,” Summers says, since dad is only about a centimeter or two long himself.

These baby pools are pretty empty: home to only some algae, maybe some small insects. “The good news is that your offspring are not likely to get eaten; the bad side is that they don’t have anything to eat,” Summers says.
This is where the begging comes in. Frogs can’t make milk like mammals or regurgitate bugs like birds. But this species is one of the rare frogs whose moms, after considerable persuading, will lay an unfertilized egg for the tadpoles’ breakfast.
When parents show up on their weekly visit, a youngster stops regular swimming, noses up to a parent and goes into a frenzy of vibrating its tail. “The parent cannot miss a hungry tadpole,” Summers says.

Bouts of persuasion go on for several hours as the tadpole begs, stops, begs more and then more. Mom often makes several false starts, entering the pool but leaving it without any egg action. During all this, “dad will be the cheerleader,” calling in trills and stroking her, Summers says.

Analyzing tadpole frenzies in the lab, Summers’ then-student Miho Yoshioka found that tadpoles on short rations begged more as hungry weeks dragged on. Parents fed these hungrier tadpoles more reliably than the babies that researchers slipped treats to, Yoshioka, Summers and Casey Meeks report in the March Animal Behaviour. Overall, the researchers conclude, the relentless frenzy shows honest need, not tadpole greed.

A mushroom whose genes have been edited with molecular scissors known as CRISPR/Cas9 doesn’t need to be regulated like other genetically modified crops, the U.S. Department of Agriculture said April 13 in a letter to the mushroom’s creator. The edible fungus is the first CRISPR-edited crop to clear USDA regulation.

Yinong Yang, a plant pathologist at Penn State University, used CRISPR/Cas9 to snip out a tiny bit of one gene from the mushroom Agaricus bisporus. The edit reduces browning when the mushroom is sliced.

Because the gene editing left no foreign DNA behind, the USDA’s Animal and Plant Health Inspection Service determined that the mushroom poses no risk to other plants and is not likely to become a weed.

Yang says he plans to submit data about the mushroom to the U.S. Food and Drug Administration. FDA clearance isn’t required but, says Yang, “we’re not just going to start marketing these mushrooms without FDA approval.”

Scientists have discovered how one microbe plays it cool.

Until now, it was a mystery how Pseudomonas syringae bacteria turn water into ice at temperatures above a normal freezing point. P. syringae pulls off its cool trick by rearranging nearby water molecules, researchers in the United States and Germany report online April 22 in Science Advances. This chill ability makes the microbes useful in making artificial snow at ski resorts.

Researchers knew that a particular protein on the microbes’ membranes was somehow responsible for making ice form. The team found that this ice nucleation protein, inaZ, acts as a mold for ice crystals. Alternating water-repelling and water-attracting parts of the protein tug nearby water molecules into an orderly, icelike arrangement. Once arranged into an ice-promoting formation, water molecules can quickly disperse heat energy.
This alignment process becomes more prominent as water temperatures drops toward 5˚ Celsius, a degree above the freezing point of the water the team used in their experiment (which contained a heavy form of hydrogen). Outside the lab, P. syringae can crystallize water at around –2˚ C, several degrees above the temperature at which ice crystals commonly form.

Understanding how P. syringae freezes water could inform science beyond the slopes. In gardens, the bacteria can wreak havoc on frost-sensitive plants. And ice-forming bacteria play an important role in climate by affecting patterns of cloud formation and precipitation, the researchers say.

Smartphone-toting pilgrims regularly stream into northern Cambodia from all over the world. Their destination: Angkor Wat, a medieval temple that’s famous for massive towers and majestic stone carvings of Hindu gods, spirits and mythological battle scenes. The site, considered the world’s largest religious monument, drew more than 2.3 million visitors in 2014.

Angkor Wat’s sightseers encounter a study in contrasts. This architectural wonder of human civilization ascends skyward, on the verge of being engulfed by nature below. Tourists walk along a path that crosses over a moat and through the temple’s western side, the one entrance cleared of vegetation. Lush forest stops just short of the rest of the structure. Outside the moat, trees, thick ground cover and ponds dominate the landscape.
While adventurous visitors snap pictures, scientists are using high-tech approaches to uncover Angkor Wat’s hidden side, long obscured by all that vegetation. After more than a century of research on the parts of Angkor Wat that are visible with the naked eye, many scientists assumed that the site was a sacred city contained within the bounds of a square moat. But even though its name roughly translates as “temple city,” new finds show that Angkor Wat was not a sacred city at all. It was a gigantic temple connected to residential districts, canals and other structures that stretched beyond the moat and blended into a sprawling city called Greater Angkor, which covered about the same area as Berlin or Columbus, Ohio.
Angkor Wat’s unveiling by modern laser technology began in April 2012. Archaeologist Damian Evans of Cambodia’s Siem Reap Center and several colleagues made daily helicopter flights for almost two weeks over a 370-square-kilometer area around the temple. The helicopter carried $250,000 worth of special equipment that fired millions of laser pulses every few seconds at the forest below. A small percentage of those pulses zipped in between trees and foliage to the forest floor. The Earth’s hard surface bounced those laser shots back to a sensor on the helicopter. This technique, known as light detection and ranging, or lidar for short, picked up differences in the contours of the land now obscured by jungle. With the findings, researchers could draw a picture of city blocks, residential areas, dried-out ponds and other archaeological remains. Results gleaned from lidar and from new ground-based investigations appeared in the December 2015 Antiquity.

Lidar has been around since the early 1960s. Scientists have used it to measure pollutants in the atmosphere, map shorelines and guide robotic and manned vehicles around obstacles. Lower costs over the last decade have made the technology accessible to archaeologists.

With their laser eye in the sky, Evans and colleagues uncovered big surprises at Angkor Wat. Just beyond one side of the roughly 1.3-kilometer-square moat surrounding the temple, the researchers found six massive and mysterious lines of earth arranged in precise coils — as well as adjacent areas where later canal construction had apparently destroyed two more coiled mounds. These Khmer creations resemble the spiraling paths of labyrinths. Lidar-guided excavations within the moat’s boundary upended ideas about who lived on temple grounds. Rather than religious or political bigwigs, residents were workers who kept the place running. And on-the-ground research found evidence of unexplained towers, built and then demolished during Angkor Wat’s construction, as well as defensive platforms used, perhaps, to fight off invaders.
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“It’s an embarrassingly exciting time for archaeologists who study Angkor Wat,” says University of Sydney archaeologist Roland Fletcher. “Researchers have driven and walked over many of these new discoveries for a century.” Fletcher directs the Greater Angkor Project, which combines remote sensing technology with archaeological digs.

If Angkor Wat blended into Greater Angkor’s 1,000 square kilometers of urban sprawl, so did hundreds of other temples and shrines of lesser grandeur built by rulers of Southeast Asia’s Khmer Empire from the ninth to 15th centuries, he says.

“There was nothing like Greater Angkor until the advent of 19th century industrial cities,” says Fletcher, who estimates it held about 750,000 residents in the 12th and 13th centuries. Cities of around 1 million people arose in China by the ninth century, but those metropolises covered one-half or less the area of Greater Angkor. Spread-out cities in the mold of Greater Angkor became more common in the 1800s as trains and cars made long-distance travel easier. But discoveries at Greater Angkor shatter a long-standing assumption that urban sprawl was impossible without mechanical forms of transportation, he says.
City sprawl
Lidar technology revealed new structures in and around the Angkor Wat temple complex.
Tap red dots for details
Big grids
Carved inscriptions at Angkor Wat describe the structure as the pet project of Suryavarman II, who ruled the Khmer Empire from 1113 until his death in 1149. Serving first as a temple dedicated to the Hindu god Vishnu, Angkor Wat also became a mausoleum for Suryavarman II when he died.

The temple hosted Hindu ceremonies into the 13th century. In the 14th or 15th century, it became a Buddhist temple. Like tourists and scientists, Angkor Wat’s modern-day Buddhist monks had no idea that the site was once so extensive.

Lidar revealed a grid of pathways forming four rectangular blocks, each the size of a small town, that encircle the main temple inside the moat. Earthen mounds and an estimated 250 to 300 ponds — now dried-out depressions on the forest floor — dotted these gridded areas.

Excavations in 2010 and 2013, the latter guided by lidar findings, uncovered remains of modest wooden dwellings and household goods, such as pots and a ceramic cooking device, in the mounds. Archaeologist Miriam Stark of the University of Hawaii at Manoa in Honolulu led that work.

Radiocarbon dating conducted by Stark’s team indicates that houses situated around the ponds appeared at least as early as the sixth century near the eventual site of Angkor Wat. Other residences date to after the 15th century, supporting evidence — including a 17th century Japanese map of the Angkor Wat temple — of the structure becoming a Buddhist religious center.
No more than 4,500 people lived within Angkor Wat’s moated boundary in the 12th century, Fletcher estimates. His calculation is based on the account of a 13th century Chinese emissary to Greater Angkor, who wrote that one to three families shared each pond in the area around the tample.

Stone inscriptions at nearby Ta Prohm, a late–12th century Greater Angkor temple, record a workforce of 12,640 people that included only about 2,000 on-site residents. Another 66,625 people were described as being “in service” to the temple, delivering food and other supplies.

At roughly twice the size of Ta Prohm, Angkor Wat probably relied on a workforce of about 25,000, Fletcher suspects. An additional 125,000 people must have shuttled in supplies. Each Greater Angkor temple apparently supported a vast economy.

If that’s true, it makes sense that crisscrossing roads forming residential blocks fan out far beyond Angkor Wat’s moat on the 2012 lidar map. “Urban grids stretched beyond temple walls into the hinterlands,” Evans says.

Lidar data showed a comparable street network at a nearby 12th century temple, Angkor Thom. Here too, “to our complete surprise, the layout of houses and streets continues beyond the moated confines of the temple,” says archaeologist Charles Higham of the University of Otago in New Zealand. He studies Greater Angkor and is familiar with the lidar results.

Religious and political big shots lived somewhere in the urban sprawl outside Angkor Wat and other temples, Fletcher suspects. Why they did so is unclear.

Mystery coils
Finding that Angkor Wat extended far beyond its moat was unexpected. But a discovery just south of the temple’s moat was unprecedented.

Lidar unveiled long banks of earth that formed six well-preserved coiled or spiral-shaped patterns. Each formation is roughly 1 kilometer long and 0.5 kilometers wide, or about 10 times the length and width of a football field. The precise alignment of these earthworks with the moat suggests they were assembled around the time of Angkor Wat’s construction.
A ground survey in late 2012 and early 2013 determined that the coils consisted of 18-meter-wide sandbanks separated by 12-meter-wide channels. After using laser maps to locate the spirals on the ground, investigators walked through the channels searching for signs of human activity. They found no pottery or other artifacts to suggest that anyone had lived or worked there.

“Nothing like the shape and design of these spirals has been seen anywhere else,” Fletcher says.

Suryavarman II’s reasons for building the coils are unknown. These mounds might have served as raised fields for growing herbs used in temple rituals. Or the coils might have been sites of formal gardens that would have been unrivaled in size and complexity until the construction of 18th century palace gardens in Europe, Evans suggests.

Rainwater could have flowed through channels between the coils. Evans doubts, however, that enough water collected to support farming.

It’s also possible that Angkor Wat’s spiral structures held special spiritual meaning for Khmer people and had no practical use. Yet Fletcher says that nothing resembling these coiled forms appears in Hindu writings and art.
After what must have been several decades of construction coinciding with work on the temple, “the spirals may never have been completed and might never have become operational,” Evans says.

Researchers are now examining fossilized pollen recovered from the coils for signs of cultivation or gardening.

Buried towers
Another surprising discovery at Angkor Wat comes not from lidar but from ground-penetrating radar. While lidar reveals characteristics of the ground’s surface covered by vegetation, ground-penetrating radar can detect objects buried deep under several dozen meters or more of soil.

In December 2009, a team led by archaeologist Till Sonnemann of Leiden University in the Netherlands dragged a wheeled device reminiscent of a lawn mower over Angkor Wat’s vast outer section for two weeks. High-frequency radio waves emitted by the contraption bounced off buried objects, signaling locations of possible archaeological remains.

Sonnemann was looking for remnants of houses or administrative buildings from the 12th century or later. Something far more intriguing turned up.

At Angkor Wat’s western entrance, where visitors enter the grounds of the temple, the radar machine identified what looked like the foundations of eight towers. Excavations in 2010 and 2012 confirmed their existence. Foundation remains lie roughly 21 meters belowground, about 10 times as deep as an Olympic swimming pool.

Each cross-shaped foundation, held in place by walls made of a reddish rock called laterite, had a square central section bound by porches jutting out on each side. Intact shrine towers from other Khmer Empire sites, which were dedicated to various gods, feature side porches.

Angkor Wat’s former towers were intentionally destroyed, Sonnemann says. Radiocarbon dating of burned wood from the foundations suggests the towers were built around the time that work started on Angkor Wat. Demolition occurred when Angkor Wat’s outer wall and western gate were completed, Sonnemann suspects.

Perhaps 12th century residents of Greater Angkor used the gateway towers as a temporary religious shrine to the Hindu god Vishnu while erecting Suryavarman II’s temple, which was dedicated to the same deity, Sonnemann says. Of the eight towers, four formed a square that stood within a larger square formed by the four others. Angkor Wat itself features four towers arranged in a square around a central tower.

The gateway towers may have served as an outline of Angkor Wat’s permanent towers, Sonnemann speculates. But they were not identical. Remote sensing identified no remnants of a central tower at the western entrance.
Wall defenses
Tourists and researchers have long gazed at Angkor Wat’s impressive stone outer wall without realizing it holds clues to warfare between the Khmer Empire and regional foes, says archaeologist David Brotherson of the University of Sydney.

Archaeologist Christophe Pottier of the Bangkok Center in Thailand first noticed holes that had been intentionally carved in parts of the wall constructed later. When Brotherson took a closer look, he speculated that those openings once supported wooden platforms and fences.

Angkor Wat’s defenders stood on the platforms and positioned themselves between the fences to repel attacks by nearby Thai kingdoms, Brotherson proposes. Those confrontations probably took place sometime between the late 13th and early 17th centuries.

Brotherson studied 6,257 wall cavities. Most consist of groups of seven square holes, at the same height, running across the inside of the wall near its top. Sets of holes, notches and grooves also run across adjacent areas on top of the wall.
These alterations appear at spots where six nearly 20-meter-wide gaps in the wall — which probably framed wooden gates — were later filled in with stone blocks. Differences in detailing and finish distinguish original masonry from filled-in sections.

Holes on the inner part of the wall held wooden beams that supported platforms about 3.5 to 4 meters above the ground that must have had stairs at each end, Brotherson says. Angkor Wat’s fighters would have stood on platforms while raining down arrows or other weapons on attackers. Wall-top holes probably held fence posts for additional protection, he suspects. Yet researchers have found no arrowheads or other weapons and no evidence of military damage to Angkor Wat, such as wall marks from catapulted boulders or remnants of torched wooden buildings.

Still, it’s more likely that the wall’s inside holes held platforms for temple defenders to stand on than wooden roofs that sheltered people or animals underneath, Brotherson says. Gateway spaces would not have been filled in simply to construct shelter roofs, he contends. And roofs would not have required holes carved on top of the wall.

“There are no historical references to defensive fortifications at Angkor Wat,” Fletcher says. “Sometimes archaeology tells us things that history cannot.”

Tropical trajectories
Lidar’s bird’s-eye view of forest floors has guided archaeologists not only to lost parts of Angkor Wat, but to a greater appreciation of similarities between Greater Angkor and other ancient tropical cities.

Lidar surveys of west-central Belize in 2009 and 2013 showed that the ancient Maya city of Caracol sprawled across now-forested landscape much as Greater Angkor did. A dense urban area, incorporating agricultural fields into a planned city, spread 10 kilometers in all directions from central Caracol in 650. Researchers estimate that more than 140,000 people lived at Caracol (SN: 12/15/12, p. 14).

Laser maps revealed farming terraces, housing tracts and roads leading to public plazas that ranged far beyond Caracol’s urban center. Anthropologists Arlen and Diane Chase of the University of Central Florida in Orlando directed lidar research at Caracol.

At 1,000 square kilometers, Greater Angkor covered a much larger area than Caracol. “Lidar surveying has just begun, but we now know that Maya cities were shrimps compared with mighty Angkor,” says Yale University anthropologist Michael Coe, a long-time investigator of the Maya and other ancient American civilizations.
Nothing like Angkor’s street grids stretching with geometric precision toward the horizon appears at Caracol, adds Coe, who is familiar with work at both sites.

Still, common factors inspired the rise and fall of Greater Angkor, Maya urban centers such as Caracol and the tropical city of Anuradhapura in Sri Lanka between the ninth and 16th centuries, Fletcher and two colleagues concluded in the October 2015 Antiquity.

Rulers in each region directed the construction of reservoirs and canals that allowed spread-out cities to flourish. Effective water management cemented the power of kings by enabling masses of farmers to make a steady living.

Severe periods of drought, indicated by analyses of tree rings and lake sediments, strained water supplies in each tropical setting, Fletcher says. Periodic monsoon rains in Southeast Asia and Sri Lanka added insult to injury, overwhelming reservoirs and damaging canals.

Unable to supply enough water, political systems at Greater Angkor and other tropical cities crumbled, Fletcher argues. But societies didn’t vanish. Farmers reorganized into smaller communities based near coasts and along major rivers. Cultivation continued in fields that had once been part of massive cities.

Laser quest
Fletcher’s rise-and-disperse scenario for ancient tropical cities is being put to a broader test. From March to May 2015, a second set of lidar flights expanded laser mapping of northern Cambodia to a total area of 2,000 square kilometers. Researchers want to see if, like Angkor Wat, other ancient temples in the region sat in the center of dispersed settlements tied together by reservoirs, canals and ponds. Archaeological investigations based on the new lidar data are under way. Evans plans to announce initial findings in June.

Over the next 10 to 15 years, lidar technology will become smaller and cheaper, Evans predicts. Laser-wielding drones will replace lidar-toting helicopters. But laser mapping is already a game changer for tropical archaeology.

Around Angkor, “the impact of lidar data is like turning on a light after groping in the dark for over a century,” says archaeologist John Miksic of the National University of Singapore.

Suryavarman II, a politically ambitious warrior who tried to expand his kingdom by launching wars and allying himself with Imperial China, would surely celebrate Angkor Wat’s laser revival if he was around today. It’s a revival of sorts for the once-mighty king, as well.

Venus flytraps (Dionaea muscipula) make carnivory look cool. But the genes that make it possible have roots in herbivory.

Though modern flytraps eat insects, their ancestors probably didn’t. In search of clues to this transition, Rainer Hedrich of the University of Wurzburg in Germany and his colleagues looked at protein production patterns in in different parts of the plant.

Unstimulated traps seem to decode genes for similar proteins to those found in leaves, which supports the theory that traps originally evolved from foliage. Glands inside the trap, which help with digestion, share common gene expression patterns with roots — perhaps because both process nutrients.

Sensory hairs signal traps to close on prey. When an unsuspecting spider trips those trap hairs, gene expression patterns shift dramatically. Traps start producing signaling hormones and digestive enzymes. Some of these same protein pathways also help plants heal wounds inflicted by herbivores. Venus flytraps may have rewired traditional plant defense machinery to eat insects in nutrient-poor soils, Hedrich’s team writes May 4 in Genome Resarch.

The galaxy is starting to feel a little crowded. Over 1,000 planets have just been added to the roster of worlds known to orbit other stars in the Milky Way, researchers announced May 10 at a news briefing. This is the largest number of exoplanets announced at once.

Most of the 1,284 worlds are larger than Earth but smaller than Neptune. Many of those are probably big balls of gas. But over 100 of the new discoveries are smaller than 1.2 times the diameter of Earth. “Those are almost certainly rocky in nature,” said Timothy Morton, an astrophysicist at Princeton University. Nine planets also lie within the habitable zone, the distance from the star where liquid water could conceivably collect on the surface of the planet. Morton and colleagues detail their findings in the May 10 Astrophysical Journal.
This announcement roughly doubles the number of planets discovered by NASA’s planet-hunting workhorse, the Kepler space telescope, which has now found 2,325 exoplanets. Kepler spent nearly four years staring at about 150,000 stars in the constellations Cygnus and Lyra, watching for subtle dips in starlight as planets crossed in front of their suns. While Kepler has since moved on to other investigations (SN: 6/28/14, p. 7), this latest haul comes from those first four years of observing.

The planet bonanza comes courtesy of a new statistical calculation that allows researchers to feel confident that a detection is a real world. Impostors such as companion stars can mimic the signal from a planet. Traditionally, each planet candidate must be followed up with intensive observations from ground-based telescopes. But with over 4,000 candidates in the queue, confirming each one would take a long time. The calculation takes into account the details of how a passing planet should dim and brighten the starlight along with how common impostors should be and provides a reliability score for each candidate. Planets in this study are those whose score is greater than 99 percent.

Techniques such as these should help confirm planets detected by upcoming missions such as the Transiting Exoplanet Survey Satellite, scheduled to launch in late 2017. Some of those planets found by TESS will in turn come under the gaze of the James Webb Space Telescope, which will launch in 2018 and investigate their atmospheres (SN: 4/30/16, p. 32).

Editor’s Note: This story was updated May 17, 2016, to correct the key in the graphic to indicate that previously detected planets include all transiting planets discovered, not just the ones found by Kepler.