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The Maya used so much red paint that they accidentally poisoned their lakes and waterways with mercury, a new study finds.The problem was cinnabar, a vivid-red mercury-sulfide mineral that can be used as the pigment vermilion in red paint. The run-off from the paint can enter waterways, where anaerobic bacteria then transform cinnabar into highly toxic methylmercury in the sediments of lakes. Over time, the methylmercury accumulates to higher levels in the food chain.The ancient Maya, a people who lived in what is now southern Mexico and Central America and whose descendants are still around today, painted almost everything red. Archaeologists have found countless artifacts that the Maya reddened, including sculptures, monuments, walls, plazas, pottery and the dead for ceremonial funerals. Cinnabar was a common pigment in the paint they made, along with red ocher, which gets its color from a nontoxic iron mineral called hematite.But the Maya passion for the color red — which to them represented the sun, blood and life — caused an environmental disaster when the nearby waters were poisoned by the cinnabar runoff, said study first author Matthew Waters, a paleolimnologist (a scientist who studies ancient waterways) at Auburn University in Alabama."They would have seen a strange color change in the water … and a drop in its productivity, such as fish for protein," he told Live Science. The Maya depended heavily on freshwater fisheries, including for freshwater shellfish. Previous studies had already found evidence for high levels of mercury in the Maya's southern highlands and south-central lowlands, but no one had fully examined levels of the toxic mineral in Mexico's Yucatán Peninsula.To investigate, Waters and his colleagues studied mercury levels in Maya-era mud in the Yucatán, and found overwhelming signs of mercury poisoning, probably from cinnabar paint, they reported in their study, published Nov. 4 in the journal Science Advances."We did not suspect [the Maya] used it in the quantities that we were seeing," he said.Troubled watersThe study found extreme levels of mercury in sediment cores from two Maya-era sites: Cobá Lake, a shallow lake beside the Maya city of that name, and Cenote Xcach (also spelled X-Canché), a flooded sinkhole beside a ruined city in the jungle that few have excavated.The sediment cores chronicle the composition of earth and water over more than 2,000 years, and the times of mercury poisoning coincide with several periods during the Preclassic and Classic periods of the Maya civilization from about A.D. 40 to 820.Waters explained that the Environmental Protection Agency in the U.S. has determined it is unsafe to drink water with mercury levels above 2 parts per billion, while the official limit for the level of mercury in fish, where it builds up over time, is 1 part per million — any number above that means the fish can be seized by authorities.Severe poisoning occurs when the mercury levels in human blood exceed about 100 parts per billion, from drinking contaminated water or eating contaminated marine animals, such as fish. In humans, mercury poisoning can cause severe symptoms, including permanent lung damage, brain damage and death.The reddish hue of the Maya sun god Kinich Ahau, made between the sixth and ninth centuries, now housed in Mexico’s National Museum of Anthropology, shows the Maya's love for mercury. (Image credit: DeAgostini/Getty Images)The most polluted parts of the Yucatan cores had a mercury level of 2.3 parts per million, the team discovered. "They experienced this for decades and, in one case, for centuries," Waters said.The researchers then examined the sediment cores for signs of environmental damage caused by the mercury poisoning. They found that the cores lacked tiny fossils of freshwater shellfish, indicating that the high mercury levels were killing marine life. The team also noticed that the sediment cores had hardly any traces of algal blooms, which should have happened frequently, Waters said. That's likely because algae could not survive in the poisoned water nutrients.Maya collapseRelated storiesWhy did the Maya civilization collapse?2,200-year-old grave in China contains 'Red Princess of the Silk Road' whose teeth were painted with a toxic substance13-year drought crippled Maya on Yucatán Peninsula 1,000 years ago, study findsScholars debate why the Maya civilization collapsed in the eighth and ninth centuries, but a leading suspect is the disruption of food supplies caused by drought.But although mercury levels were high during the Preclassic and Classic periods, the environmental damage caused by mercury levels had been falling in many places for hundreds of years by the time of the Maya collapse, Waters said, although it may have been a contributing factor.Cinnabar does not occur naturally in the Yucatán, so it must have been imported there, probably from what's now Honduras, the researchers said. It seems these cinnabar imports eventually stopped at Cobá Lake, and the poisoning there fell to a background level of about 20 parts per billion by A.D. 520. However, the sediment cores showed that the mercury poisoning continued at Cenote Xcach until the collapse, they said. What do you know about the civilization that built pyramids across Mesoamerica? Find out with our ancient Maya quiz.

A geological reorganization near Japan may have led to the formation of one of North America's most recognizable features. The birth of the Gulf of California, which rifted from Mexico and created the Baja Peninsula 6 million to 8 million years ago, was accelerated by the formation of a double subduction zone more than 6,000 miles (9,600 kilometers) away, near Japan. This reorganization led to a transfer of tectonic force across the Pacific tectonic plate, which, in turn, opened the Gulf of California and ultimately led to the Grand Canyon's formation, according to new research published Oct. 29 in the journal Science.The findings will help researchers understand more about plate boundaries, which is where most of the strongest earthquakes on the planet originate. "It's more than a regional curiosity," study co-author Thorsten Becker, a geophysicist at the University of Texas at Austin (UT Austin), told Live Science. "It's a reminder of the global connectedness of mantle convection and plate tectonics."The Gulf of California is an example of a rift zone, a place where continental crust pulls apart and creates a spot so low that it can be filled by ocean water. There are many rift zones around the world; a currently active one is the Red Sea. But rifting can slow down, speed up or peter out entirely. In the Gulf of California, rifting not only persisted, but sped up. Rifting took about 6 million to 13 million years ‪—‬ much quicker than the typical speed of 30 million to 80 million years. Study co-author Guido Gianni, a geophysicist at the Czech Academy of Sciences, wondered why that was. No previous research fully explained the rapid rifting, which changed the face of North America in many ways. Not only did the rifting transfer Baja California to the Pacific Plate, but it provided an outlet for the developing Colorado River, which subsequently carved the Grand Canyon on its way to sea level.Gianni and Becker's doctoral student at UT Austin, Xiang He, used a global model of plate tectonics, run on supercomputers at the Texas Advanced Computing Center on campus, to find out if far-flung forces might provide an explanation. Around the same time the Gulf of California was pulling apart, Japan was undergoing its own geological changes. Off the coast of Japan, the Pacific Plate subducts, or pushes under, the Eurasian Plate. About 10 million to 12 million years ago, a single subduction zone near Japan transitioned into two separate subduction zones. A double subduction zone off Japan (left inset) accelerated the growth of the Gulf of California (right inset). (Image credit: He et al.)This transition at the western end of the Pacific Plate influenced the tectonic forces on the other side of the plate, He, Gianni, Becker and their colleagues found. "It turned out — ta-da! — [with] the change in this pulling stress, Baja California was one of the few places outside the Japan region that were affected," Becker said. It was "unexpected and sort of a little bit too good to be true." The researchers tweaked their model to see if the result held with different assumptions about stresses and mantle properties, and it did. influenced the tectonic forces on the other side of the plate, He, Gianni, Becker and their colleagues found. "It turned out — ta-da! — [with] the change in this pulling stress, Baja California was one of the few places outside the Japan region that were affected," Becker said. It was "unexpected and sort of a little bit too good to be true." The researchers tweaked their model to see if the result held with different assumptions about stresses and mantle properties, and it did. Related stories'The system is critically stressed': San Andreas and San Jacinto faults scarily close to major earthquake, study findsFragment of lost tectonic plate discovered where San Andreas and Cascadia faults meetScars from ancient 'megaquakes' at Cascadia subduction zone discovered in deep-sea landslidesThe Gulf of California was already rifting regardless of the situation across the Pacific. The initial rift was caused by the subduction of a tectonic plate called the Farallon Plate, located under the West Coast of North America. The Farallon slab stretched and thinned the continental crust of the North American plate as it moved. But such rifting might have ended with nothing more than the formation of a little valley or low spot if Japan's influence had not kicked in to give the rifting some extra oomph. The findings have a direct effect on scientists' understanding of how plate boundaries form, Becker said. And this isn't just academic. The findings could have implications for understanding earthquake-generating faults such as the San Andreas in California and the Cascadia subduction zone in the Pacific Northwest, Becker said. Cascadia is what's known as a "megathrust" boundary, capable of triggering quakes of more than magnitude 9. "If I'm asking what is the mantle doing underneath Cascadia so I get our megathrust correct," Becker said, "I need to include these effects."

It's a common observation that women often prefer warmer temperatures and feel cold more easily than men do, and the same trend appears among females of other species. Now, a study offers new clues as to what drives this preference — and testosterone may play a part. Skin carries sensors to detect heat and cold that influence each organism's decision to stay in or move out of an environment. The new study, published Oct. 28 in the Journal of Physiology, found that these sensors activate at higher temperatures in female mice, which appears to shift their preferred temperature roughly 7 degrees Fahrenheit (4 degrees Celsius) higher than that of male mice. Testosterone seems to influence this difference in activation. "You could say it's just a cute observation of no particular importance," said study co-author Peter McNaughton, a pharmacologist at King's College London who studies pain, thermal sensation and thermoregulation. "[But] it's got practical ramifications," in that it might be important in designing buildings and spaces that accommodate people, he told Live Science. A distinct temperature preferenceProteins in the skin's nerve endings activate in response to warmth or cold. "You can look at them like little electrical generators in the nerve endings," said Dr. Michael Caterina, a neuroscientist at Johns Hopkins University who was not involved in the research. When activated, these proteins allow charged ions to enter sensory nerve cells, which, in turn, transmit electrical signals to the brain. The circuits a given nerve cell connects to determines our perception of heat or cold, Caterina told Live Science. Beyond humans, it is known that many female animals, including mice and birds, prefer slightly warmer temperatures than their male counterparts do. So the researchers set up an experiment to investigate these differences.They put 30 male and 27 female mice on two adjacent plates of different temperatures — one at 91.4 degrees Fahrenheit (33 degrees Celsius) and another that varied between lower and higher temperatures. A camera tracked the mice's movements and calculated how much time they spent on each plate. Both male and female mice spent more time at the 91.4 F plate when the second plate was cooler. However, when put next to a plate measuring 100.4 F (38 C), female mice spent significantly more time on the warmer plate than male mice did. The average preferred surface temperature was approximately 89.6 F (32 C) for male mice and 96.8 F (36 C) for female mice."Since the top of the cage was completely open, there was no question of the air temperature affecting the mice," McNaughton said, so the preference was driven solely by the sensors in their skin. The researchers also measured the internal and skin temperatures of the mice and confirmed that there were no significant differences between the sexes on those fronts.The role of testosterone The scientists explored what would happen if they genetically deleted the warmth-detector protein. In male mice, this reduced their avoidance of the warmer plate, suggesting this protein normally sends a signal that discourages them from staying on warmer surfaces. The mice's preferred temperature also rose to about 95 F (35 C), closer to that of females.The study suggests that testosterone somehow tweaks the function of heat-sensing nerves in the skin. (Image credit: Alllex via Getty Images)In female mice, deleting or blocking the protein did not have any significant effect. The team then tried eliminating or blocking the coolness-detecting protein, finding that males and females didn't avoid the cool plates as strongly as they did before. Female mice also spent less time on the warmer plates, but males' preference for the warmer plates didn't change."Females are a little bit more responsive to activation of the cold receptor," Caterina said, "and a little bit less responsive to activation of the warmer receptor." That's despite the temperature-sensing neurons in both sets of mice working identically, the team found.The researchers suspected that sex hormones might help to explain this difference.They gave a group of male mice a drug that blocks the production of testosterone. Weeks after the treatment, these mice spent more time on the 38 C plate than males with normal testosterone. Meanwhile, female mice given testosterone lost their preference for warmer temperatures. Interestingly, giving male mice female hormones, including forms of estrogen and progesterone, did not affect their temperature preferences. And blocking the hormones in female mice also had no effect. These hormones are known to influence other aspects of temperature regulation in the body, though, such as heat dissipation through the skin; but in this case, they didn't seem to affect animals' perception of temperature."So it really seems as though testosterone is the most important determinant," McNaughton said. But these changes were only partial; testosterone did not completely reverse the differences between the sexes. "So there is something else going on that we weren't able to identify," he added.The exact mechanism for how testosterone impacts the sensor proteins is not clear. Because the effect happened over weeks, researchers suggested that it did not directly affect the temperature-sensing proteins. It might instead act indirectly by influencing the activity of genes, but further studies would be needed to confirm this idea.Related storiesDo women get cold more easily than men?Can humans sense wetness?Warm and cool temperatures travel on completely different paths to the brain, study findsAlthough the researchers did not conduct any tests in humans, McNaughton noted that the same sensor proteins are present in people and that studies with humans suggest that they behave in a similar way.This research provides "valuable information" for understanding how the proteins responsible for sensing temperature work, Caterina said. Understanding these mechanisms could be useful for studying conditions like neuropathic pain, in which people's sensitivity to heat and cold is enhanced."What kinds of signals create our daily experiences around temperature is by itself very important," he told Live Science. "It's a big part of understanding ourselves as living beings." This article is for informational purposes only and is not meant to offer medical advice.

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