Locations of ancient Maya sacred groves of cacao trees discovered

For as much as modern society worships chocolate, cacao -- the plant chocolate comes from -- was believed to be even more divine to ancient Mayas. The Maya considered cacao beans to be a gift from the gods and even used them as currency because of their value.

As such, cacao bean production was carefully controlled by the Maya leaders of northern Yucatan, with cacao trees only grown in sacred groves. But no modern researcher has ever been able to pinpoint where these ancient sacred groves were located -- until now.

Researchers at Brigham Young University, including professor emeritus Richard Terry and graduate students Bryce Brown and Christopher Balzotti, worked closely with archaeologists from the U.S. and Mexico to identify locations the Maya used to provide the perfect blend of humidity, calm and shade required by cacao trees. While the drier climate of the Yucatan peninsula is inhospitable to cacao growth, the team realized the vast array of sinkholes common to the peninsula have microclimates with just the right conditions.

As detailed in a study newly published in the Journal of Archaeological Science Reports, the team conducted soil analyses on 11 of those sinkholes and found that the soil of nine of them contained evidence of theobromine and caffeine -- combined biomarkers unique to cacao. Archaeologists also found evidence of ancient ceremonial rituals -- such as staircase ramps for processions, stone carvings, altars and offerings like jade and ceramics (including tiny ceramic cacao pods) -- in several sinkholes.

"We looked for theobromine for several years and found cacao in some places we didn't expect," said Terry, who recently retired from BYU. "We were also amazed to see the ceremonial artifacts. My students rappelled into one of these sinkholes and said, 'Wow! There is a structure in here!' It was a staircase that filled one-third of the sinkhole with stone."

To extract and analyze the sinkhole soil for cacao biomarkers -- specifically theobromine and caffeine -- the team developed a new method of soil extraction. This involved drying the soil samples and passing them through a sieve, covering them with hot water, having them centrifuged and passed through extraction disks, and analyzing the extracts by mass spectrometry. To increase the sensitivity of their testing, the research team compared the results of the soil samples to seven control samples with no history of exposure to the biomarkers.

The findings of the BYU study indicate that cacao groves played an important role in ancient rituals and trade routes of the ancient Maya, impacting the entirety of the Mesoamerican economy. A 70-mile Maya "highway" in the area that was the main artery for trade passes near hundreds of sinkholes, so it is likely that the leaders who commissioned the highway development also controlled cacao production. The evidence of cacao cultivation alongside archaeological findings also supports the idea that cacao was important in the ideological move from a maize god to a sun god.

In one sinkhole near Coba, Mexico, a village 45 minutes from modern day Tulum, the research team found the arm and bracelet of a figurine attached to an incense jar and several ceramic modeled cacao pods. They also found remnant cacao trees growing there, making it quite possible that this sinkhole, named "Dzadz Ion," was the location of a sacred cacao grove during the Late Postclassic period (About A.D. 1000 to 1400).

"Now we have these links between religious structures and the religious crops grown in these sinkholes," Terry said. "Knowing that the cacao beans were used as currency, it means the sinkholes were a place where the money could be grown and controlled. This new understanding creates a rich historical narrative of a highly charged Maya landscape with economic, political and spiritual value."

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Ancient Maya lessons on surviving drought

A new study casts doubt on drought as the driver of ancient Mayan civilization collapse.

There is no dispute that a series of droughts occurred in the Yucatan Peninsula of southeastern Mexico and northern Central America at the end of the ninth century, when Maya cities mysteriously began to be depopulated. Believing the Maya were mostly dependent on drought-sensitive corn, beans, and squash, some scholars assume the droughts resulted in starvation.

However, a new analysis by UC Riverside archaeologist Scott Fedick and plant physiologist Louis Santiago shows the Maya had nearly 500 edible plants available to them, many of which are highly drought resistant. The results of this analysis have now been published in the Proceedings of the National Academy of Sciences.

"Even in the most extreme drought situation -- and we have no clear evidence the most extreme situation ever occurred -- 59 species of edible plants would still have persisted," Santiago said.

Some of the toughest plants the Maya would have turned to include cassava with its edible tubers, and hearts of palm. Another is chaya, a shrub domesticated by the Maya and eaten today by their descendants. Its leaves are high in protein, iron, potassium, and calcium.

"Chaya and cassava together would have provided a huge amount of carbohydrates and protein," Santiago said.

Unable to find a master list of indigenous Maya food plants, Fedick recently compiled and published one that draws on decades of Maya plant knowledge. Faced with much speculation about drought as the cause of Maya social disruptions, he and Santiago decided to examine all 497 plants on the list for drought tolerance.

"When botanists study drought resistance, they're usually talking about a specific plant, or a particular ecosystem," Fedick said. "One of the reasons this project was so challenging is because we examined the dietary flora of an entire civilization -- annuals, perennials, herbs, trees, domesticates, and wild species. It was a unique endeavor."

Though the researchers do not have a clear answer about why ancient Maya society unraveled, they suspect social and economic upheaval played a role.

"One thing we do know is the overly simplistic explanation of drought leading to agricultural collapse is probably not true," Fedick said.

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Archaeologists discover salt workers’ residences at underwater Maya site

The ancient Maya had stone temples and palaces in the rainforest of Central America, along with dynastic records of royal leaders carved in stone, but they lacked a basic commodity essential to daily life: salt. The sources of salt are mainly along the coast, including salt flats on the Yucatan coast and brine-boiling along the coast of Belize, where it rains a lot. But how did the inland Maya maintain a supply of salt?

LSU Maya archaeologist Heather McKillop and her team have excavated salt kitchens where brine was boiled in clay pots over fires in pole and thatch buildings preserved in oxygen-free sediment below the sea floor in Belize. But where these salt workers lived has been elusive, leaving possible interpretations of daily or seasonal workers from the coast or even inland. This gap left nagging questions about the organization of production and distribution.

New findings on the organization of the salt industry to supply this basic dietary commodity to inland cities during the Classic Maya civilization are reported in a recent article by McKillop and LSU alumna Cory Sills, who is an associate professor at University Texas-Tyler. The article "Briquetage and brine: Living and Working at the Ek Way Nal Salt Works, Belize" was published in the journal Ancient Mesoamerica.

McKillop and Sills began this new project in search of residences where the salt workers lived and to understand the energetics of production of salt with funding from the National Science Foundation. Although field work at Ek Way Nal, where the Paynes Creek Saltworks is located, has been postponed since March 2020 due to the pandemic, the researchers turned to material previously exported for study in the LSU Archaeology lab, including hundreds of wood samples from pole and thatch buildings, as well as pottery sherds.

"The Archaeology lab looks like a Tupperware party, with hundreds of plastic containers of water, but they are keeping the wood samples wet so they don't dry out and deteriorate," said McKillop, who is the Thomas & Lillian Landrum Alumni Professor in the LSU Department of Geography and Anthropology.

She explained the strategy to continue research in the lab: "I decided to submit a wood post sample for radiocarbon dating from each building at Ek Way Nal to see if they all dated to the same time, which was suggested by the visibility of artifacts and buildings on the sea floor."

When the dates started coming in, two at a time, McKillop identified a building construction sequence that began in the Late Classic at the height of Maya civilization and continued through the Terminal Classic when the dynastic leaders of inland city states were losing control and eventually the cities were abandoned by A.D. 900.

According to McKillop, "Using the well-studied site, Sacapulas, Guatemala, as a model, worked well to develop archaeological expectations for different activities for brine boiling in a salt kitchen, a residence and other activities, including salting fish."

In the Ancient Mesoamerica article, they report a 3-part building construction sequence with salt kitchens, at least one residence and an outdoor area where fish were salted and dried. The archeologists' strategy of radiocarbon dating each building had produced a finer grain chronology for Ek Way Nal that they are using for more sites.

The new analysis verifies McKillop's estimate that 10 salt kitchens were in production at a time at the Paynes Creek Salt Works, which she reported in her book "Maya Salt Works" (2019, University Press of Florida).

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Maya more warlike than previously thought

The Maya of Central America are thought to have been a kinder, gentler civilization, especially compared to the Aztecs of Mexico. At the peak of Mayan culture some 1,500 years ago, warfare seemed ritualistic, designed to extort ransom for captive royalty or to subjugate rival dynasties, with limited impact on the surrounding population.

Only later, archeologists thought, did increasing drought and climate change lead to total warfare -- cities and dynasties were wiped off the map in so-called termination events -- and the collapse of the lowland Maya civilization around 1,000 A.D. (or C.E., current era).

New evidence unearthed by a researcher from the University of California, Berkeley, and the U.S. Geological Survey calls all this into question, suggesting that the Maya engaged in scorched-earth military campaigns -- a strategy that aims to destroy anything of use, including cropland -- even at the height of their civilization, a time of prosperity and artistic sophistication.

The finding also indicates that this increase in warfare, possibly associated with climate change and resource scarcity, was not the cause of the disintegration of the lowland Maya civilization.

"These data really challenge one of the dominant theories of the collapse of the Maya," said David Wahl, a UC Berkeley adjunct assistant professor of geography and a researcher at the USGS in Menlo Park, California. "The findings overturn this idea that warfare really got intense only very late in the game."

"The revolutionary part of this is that we see how similar Mayan warfare was from early on," said archaeologist Francisco Estrada-Belli of Tulane University, Wahl's colleague. "It wasn't primarily the nobility challenging one another, taking and sacrificing captives to enhance the charisma of the captors. For the first time, we are seeing that this warfare had an impact on the general population."

Total warfare

The evidence, reported today in the journal Nature Human Behaviour, is an inch-thick layer of charcoal at the bottom of a lake, Laguna Ek'Naab, in Northern Guatemala: a sign of extensive burning of a nearby city, Witzna, and its surroundings that was unlike any other natural fire recorded in the lake's sediment.

The charcoal layer dates from between 690 and 700 A.D., right in the middle of the classic period of Mayan civilization, 250-950 A.D. The date for the layer coincides exactly with the date -- May 21, 697 A.D. -- of a "burning" campaign recorded on a stone stela, or pillar, in a rival city, Naranjo.

"This is really the first time the written record has been linked to an event in the paleo data sets in the New World," Wahl said. "In the New World, there is so little writing, and what's preserved is mostly on stone monuments. This is unique in that we were able to identify this event in the sedimentary record and point to the written record, particularly these Mayan hieroglyphs, and make the inference that this is the same event."

Wahl, a geologist who studies past climate and is first author of the study, worked with USGS colleague Lysanna Anderson and Estrada-Belli to extract 7 meters of sediment cores from the lake. Laguna Ek'Naab, which is about 100 meters across, is located at the base of the plateau where Witzna once flourished and has collected thousands of years of sediment from the city and its surrounding agricultural fields. After seeing the charcoal layer, the archaeologists examined many of Witzna's ruined monuments still standing in the jungle and found evidence of burning in all of them.

"What we see here is, it looks like they torched the entire city and, indeed, the entire watershed," Wahl said. "Then, we see this really big decrease in human activity afterwards, which suggests at least that there was a big hit to the population. We can't know if everyone was killed or they moved or if they simply migrated away, but what we can say is that human activity decreased very dramatically immediately after that event."

This one instance does not prove that the Maya engaged in total warfare throughout the 650-year classic period, Estrada-Belli said, but it does fit with increasing evidence of warlike behavior throughout that period: mass burials, fortified cities and large standing armies.

"We see destroyed cities and resettled people similar to what Rome did to Carthage or Mycenae to Troy," Estrada-Belli said.

And if total warfare was already common at the peak of Mayan lowland civilization, then it is unlikely to have been the cause of the civilization's collapse, the researchers argue.

"I think, based on this evidence, the theory that a presumed shift to total warfare was a major factor in the collapse of Classic Maya society is no longer viable," said Estrada-Belli. "We have to rethink the cause of the collapse, because we're not on the right path with warfare and climate change."

'Bahlam Jol burned for the second time'

Though Mayan civilization originated more than 4,000 years ago, the Classic period is characterized by widespread monumental architecture and urbanization exemplified by Tikal in Guatemala and Dzibanché in Mexico's Yucatan. City-states -- independent states made up of cities and their surrounding territories -- were ruled by dynasties that, archaeologists thought, established alliances and waged wars much like the city-states of Renaissance Italy, which affected the nobility without major impacts on the population.

In fact, most archaeologists believe that the incessant warfare that arose in the terminal Classic period (800-950 A.D.), presumably because of climate change, was the major cause of the decline of Mayan cities throughout present day El Salvador, Honduras, Guatemala, Belize and Southern Mexico.

So when Wahl, Anderson and Estrada-Belli discovered the charcoal layer in 2013 in Laguna Ek'Naab -- a layer unlike anything Wahl had seen before -- they were puzzled. The scientists had obtained the lake core in order to document the changing climate in Central America, hoping to correlate these with changes in human occupation and food cultivation.

The puzzle lingered until 2016, when Estrada-Belli and co-author Alexandre Tokovinine, a Mayan epigrapher at the University of Alabama, discovered a key piece of evidence in the ruins of Witzna: an emblem glyph, or city seal, identifying Witzna as the ancient Mayan city Bahlam Jol. Searching through a database of names mentioned in Mayan hieroglyphs, Tokovinine found that very name in a "war statement" on a stela in the neighboring city-state of Naranjo, about 32 kilometers south of Bahlam Jol/Witzna.

The statement said that on the day ." .. 3 Ben, 16 Kasew ('Sek'), Bahlam Jol 'burned' for the second time." According to Tokovinine, the connotation of the word "burned," or puluuy in Mayan, has always been unclear, but the date 3 Ben, 16 Kasew on the Mayan calendar, or May 21, 697, clearly associates this word with total warfare and the scorched earth destruction of Bahlam Jol/Witzna.

"The implications of this discovery extend beyond mere reinterpretation of references to burning in ancient Maya inscriptions," Tokovinine said. "We need to go back to the drawing board on the very paradigm of ancient Maya warfare as centered on taking captives and extracting tribute."

Three other references to puluuy or "burning" are mentioned in the same war statement, referencing the cities of Komkom, known today as Buenavista del Cayo; K'an Witznal, now Ucanal; and K'inchil, location unknown. These cities may also have been decimated, if the word puluuy describes the same extreme warfare in all references. The earlier burning of Bahlam Jol/Witzna mentioned on the stela may also have left evidence in the lake cores -- there are three other prominent charcoal layers in addition to the one from 697 A.D. -- but the date of the earlier burning is unknown.

Mayan archaeologists have reconstructed some of the local history, and it's known that the conquest of Bahlam Jol/Witzna was set in motion by a queen of Naranjo, Lady 6 Sky, who was trying to reestablish her dynasty after the city-state had declined and lost all its possessions. She set her seven-year-old son, Kahk Tilew, on the throne and then began military campaigns to wipe out all the rival cities that had rebelled, Estrada-Belli said.

"The punitive campaign was recorded as being waged by her son, the king, but we know it's really her," he said.

That was not the end of Bahlam Jol/Witzna, however. The city revived, to some extent, with a reduced population, as seen in the lake cores. And the emblem glyph was found on a stela erected around 800 A.D, 100 years after the city's destruction. The city was abandoned around 1,000 A.D.

"The ability to tie geologic evidence of a devastating fire to an event noted in the epigraphic record, made possible by the relatively uncommon discovery of an ancient Maya city's emblem glyph, reflects a confluence of findings nearly unheard of in the field of geoarchaeology," Wahl said.

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Researchers find ancient Maya farms in Mexican wetlands

UC assistant professor Christopher Carr examines an ancient quarry in Yaxnohcah, Mexico.

Archaeologists with the University of Cincinnati used the latest technology to find evidence suggesting ancient Maya people grew surplus crops to support an active trade with neighbors up and down the Yucatan Peninsula.

They will present their findings at the annual American Association of Geographers conference in Washington, D.C.

The Mayan civilization stretched across portions of Mesoamerica, a region spanning Mexico and Central America. The oldest evidence of Maya civilization dates back to 1800 B.C., but most cities flourished between 250 and 900 A.D. By the time Spanish ships arrived in the 1500s, some of the biggest cities were deserted. Researchers at UC are trying to piece together the life history of the Maya before the Spanish conquest.

Nicholas Dunning, a professor of geography in UC's McMicken College of Arts and Sciences, was part of a research team that found evidence of cultivation along irregular-shaped fields in Mexico that followed the paths of canals and natural water channels at a place called Laguna de Terminos on the Gulf of Mexico. The archaeologists expect to find evidence of habitation when they begin excavations.

The extensive croplands suggest the ancient Maya could grow surplus crops, especially the cotton responsible for the renowned textiles that were traded throughout Mesoamerica.

"It was a much more complex market economy than the Maya are often given credit for," Dunning said.

Local workers brought the Laguna de Terminos site to the attention of researchers about seven years ago.

"A forester working in the area said there seemed to be a network of ancient fields," Dunning said. "I looked on Google Earth and was like, 'Whoa!' It was an area in the Maya Lowlands that I'd never paid any attention to. And obviously not a lot of other people had, either, from the perspective of looking at ancient agriculture."

Satellite images revealed a patchwork quilt of blocks along drainage ditches that suggested they were built. Archaeologist also studied imagery NASA created of the region using a tool called Light Detection and Ranging, or LIDAR, that can depict the contours of the ground beneath the leafy canopy of trees and vegetation. Their review confirmed Dunning's suspicions: the area was covered in ancient farm fields.

"It appears they developed fairly simply from modifications of existing drainage along the eastern edge of the wetlands," Dunning said. "They probably deepened and straightened some channels or connected them in places, but then further expanded the fields with more sophisticated hydro-engineering."

LIDAR gives scientists a never-before-seen picture of the Earth's surface even after centuries of unchecked jungle growth conceals the remains of ancient structures. Researchers look for telltale signs of human activity: squares and rectangles indicating old foundations and circular pits from human-made reservoirs and quarries where the chert used in stone tools was mined. On the LIDAR maps, any hidden structures pop out, including ancient roads and former villages.

"That's the magic of LIDAR," UC assistant research professor Christopher Carr said.??Carr spent a career practicing engineering before returning to UC to study and eventually teach in the geography department. He approaches questions about the ancient Maya from an engineer's perspective.

Carr pointed to a map of Yaxnohcah, Mexico, showing a small reservoir the ancient Maya apparently dug in a wetland far from cultivated fields or known settlements.

"What were my ancient counterparts thinking when they built that water reservoir? What did they want to accomplish?" he asked.

Carr also used the LIDAR imagery in the project to follow an ancient Maya road that perhaps hasn't been traveled in more than 1,000 years. The road is perfectly visible on the LIDAR map but is virtually impossible to discern when you are standing right on it, Carr said.

"There's vegetation everywhere. But when you've been doing this for a while, you notice little things," Carr said. "I'll have a LIDAR image on my smartphone that shows me where I am, but I don't see anything but rainforest. You just walk back and forth until you can feel something underfoot and follow it."

Identifying possible roads is important for another interest of the UC researchers: ancient Maya marketplaces. Dunning and Carr are working at Yaxnohcah with researchers such as Kathryn Reese-Taylor from the University of Calgary and Armando Anaya Hernandez from Universidad Autónoma de Campeche to unlock the mysteries of the ancient Maya economy. Additionally, they and graduate student Thomas Ruhl have been analyzing NASA's LIDAR imagery across the Yucatan Peninsula to identify more ancient marketplaces.

Unlike pyramids or even many homes, marketplaces had no foundations or permanent structures, researchers said. They were built on low platforms or cleared areas, perhaps like a seasonal fair or flea market. But they were an important part of life in Maya culture

Dunning said the presence of roads between Maya cities would lend credence to the value the ancient Maya placed on trade with their neighbors. He thinks some of the larger squares identified on the LIDAR maps represent these open markets.

"In some areas, they have this very distinct physical signature," Dunning said. "So far, we've identified several possible marketplaces. We don't know for sure that they're marketplaces, but they have an architectural layout that is suggestive of one."

Soil analysis at other locations identified evidence of ancient butcher shops and stone masons. Dunning solicited the help of UC's botanists who are conducting analyses that might shed light on his marketplace hypothesis. But the LIDAR maps themselves are instructive.

"I look at spatial patterns. If you look at these big structures and small pyramids, you can tell they're important structures," Carr said. "And then you have this 'lightweight' thing next to it. That's what a marketplace looks like to me."

Dunning said the ancient Maya likely sold perishable goods such as maize and a starchy tuber called manioc. And they traded "mantas," or bolts of the ornate and richly patterned textiles made from the cotton they grew. These were prized by the Spaniards who arrived in the 1600s.

"We don't have direct evidence of what the textiles look like in this area. But if you look at ancient paintings and sculptures, people were wearing very elaborate garments," Dunning said.

Dunning first explored the historic sites of the Yucatan Peninsula at age 14 when he and his older brother drove down to Mexico from Illinois.

"We took a train to the Yucatan and used public transportation to get around to the sites," Dunning said.

He applied to the University of Chicago partly because it offered a Mayan language class. Dunning returned to Mexico while in college to conduct his first field research. He's been back many times since.

"My interest in archaeology is in human-environment interactions, including agriculture," Dunning said.

Dunning is learning more about how ancient Maya people shaped their world to overcome challenges and take advantage of natural opportunities. Dunning's work also took him to a place called Acalan near the Gulf of Mexico.

"Roughly translated, Acalan means 'place of canoes' because it's very watery," Dunning said. "And getting around by water is far easier than any other means in that area."

Then as now the region is covered in thick tropical rainforest. Researchers have to be wary of cheeky monkeys that will throw fruit or worse from the treetops. Carr said one encounter left him sore for days.

"There was this aggressive spider monkey. He'd seen me a couple days earlier. And he's back shaking the trees," Carr said. "And all of a sudden, I'm lying flat on the ground. A branch hit me in the shoulder and knocked me to the ground."

Visiting archaeologists at Yaxnohcah stay at a former Army outpost that was converted into a staffed research station.

"Living conditions are actually luxurious by camping standards. You're in the field all day and you're dirty and tired. But you can take a shower. And when you're finished, someone has cooked you a meal," Carr said.

At Laguna de Terminos, UC researchers are working to collect clues about the ancient Maya before they are lost to development. Many of the wetlands are being drained or plowed up for grazing pasture.?

Dunning said ironically these low-yield pastures provide far less economic value to today's farmers than the seeming bounty of crops the ancient Maya derived from them more than 1,000 years ago. Their study warns the land-use practices are causing environmental damage to some of these valuable wetlands.

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Carbon reserves in Central American soils still affected by ancient Mayan deforestation

This is an ancient stone carving of the Maya God Pauahtun, taken at Copan Ruinas, Honduras.

Deforestation is suspected to have contributed to the mysterious collapse of Mayan civilization more than 1,000 years ago. A new study shows that the forest-clearing also decimated carbon reservoirs in the tropical soils of the Yucatan peninsula region long after ancient cities were abandoned and the forests grew back.

The findings, published in the journal Nature Geoscience, underscore how important soils and our treatment of them could be in determining future levels of greenhouse gases in the planet's atmosphere.

The Maya began farming around 4,000 years ago, and the spread of agriculture and building of cities eventually led to widespread deforestation and soil erosion, previous research has shown. What's most surprising in the new study is that the soils in the region haven't fully recovered as carbon sinks in over a millennium of reforestation, says McGill University geochemist Peter Douglas, lead author of the new paper.

Ecosystem 'fundamentally changed'

"When you go to this area today, much of it looks like dense, old-growth rainforest," says Douglas, an Assistant Professor of Earth and Planetary Sciences at McGill. "But when you look at soil carbon storage, it seems the ecosystem was fundamentally changed and never returned to its original state."

Soil is one of the largest storehouses of carbon on Earth, containing at least twice as much carbon as today's atmosphere. Yet scientists have very little understanding of how soil carbon reservoirs change on timescales longer than a decade or so. The new study, along with other recently published research, suggests that these reservoirs can change dramatically on timescales spanning centuries or even millennia.

To investigate these long-term effects, Douglas and his co-authors examined sediment cores extracted from the bottom of three lakes in the Maya Lowlands of southern Mexico and Guatemala. The researchers used measurements of radiocarbon, an isotope that decays with time, to determine the age of molecules called plant waxes, which are usually stored in soils for a long time because they become attached to minerals. They then compared the age of wax molecules with that of plant fossils deposited with the sediments.

The team -- which included scientists from Yale University, ETH Zurich, the University of Florida and the University of Wisconsin-Superior -- found that once the ancient Maya began deforesting the landscape, the age difference between the fossils and the plant waxes went from being very large to very small. This implies that carbon was being stored in soils for much shorter periods of time.

The project stemmed from research that Douglas had done several years ago as a PhD student at Yale, using plant-wax molecules to trace past climate change affecting the ancient Maya. At the same time, work by other researchers was indicating that these molecules were a good tracer for changes in soil-carbon reservoirs. "Putting these things together, we realized there was an important data-set here relating ancient deforestation to changes in soil carbon reservoirs," Douglas explains.

Protecting old-growth tropical forests

"This offers another reason -- adding to a long list -- to protect the remaining areas of old-growth tropical forests in the world," Douglas says. "It could also have implications for how we design things like carbon offsets, which often involve reforestation but don't fully account for the long-term storage of carbon." (Carbon offsets enable companies or individuals to offset their greenhouse-gas emissions by purchasing credits from environmental projects, such as tree-planting.)

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