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Most mammals take 12 seconds to defecate
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Scotland floats on a hot starry plume THE plume of hot rock that sits beneath Iceland has long-reaching fingers – two of which stretch all the way to Scotland and Norway. This perhaps explains why the breathtaking scenery of areas such as the Scottish Highlands isn’t submerged beneath the waves. Mantle plumes are like chimneys that transport hot, buoyant rock from deep inside Earth. When they break through to the surface, the volcanic activity they generate can fuel the formation of new islands, such as the Hawaiian archipelago. Iceland also owes its existence to a mantle plume – and seismic maps of Earth’s interior suggest that this plume doesn’t have the typical circular outline. “It’s far more irregular,” says Nicky White at the University of Cambridge. In fact, it looks a bit like flower petals or a star shape on top of a chimney of rising hot rock (see diagram, right). But why or how that irregularity arises has
Most mammals take 12 seconds to defecate EVERYONE poops, and we all take about the same amount of time to do it. A study of the hydrodynamics of defecation finds that all mammals producing faeces similar to ours take 12 seconds on average to relieve themselves. “The smell of body waste attracts predators, which is dangerous for animals. If they stay longer doing their thing, they’re exposing themselves and risking being discovered,” says Patricia Yang, a mechanical engineer 16 | NewScientist | 6 May 2017
remained a mystery until now. When White saw one particular map of the plume’s outline below Earth’s surface, it suddenly dawned on him how it might have gained its irregular shape. He recalled experiments by some of his colleagues in Cambridge. They have looked at how fluids with different viscosities mix in the confined, almost twodimensional gap between two
Europe’s splattering plume Europe’s splattering plume When hot rock rising up below Iceland reaches the asthenosphere,
100km below surface, spreads out to form long, runny fingers, When hot rockEarth’s rising up belowitIceland reaches the asthenosphere, two of which Scotland and Norwayout to form long, runny fingers, 100km belowreach Earth’s surface, it spreads two of which reach Scotland and Norway FINGERS FINGERS
MANTLE PLUME MANTLE PLUME Idealised shape of the plumeshape splatter Idealised of the plume splatter
at the Georgia Institute of Technology in Atlanta. Yang and colleagues filmed elephants, pandas and warthogs at a local zoo, and one team member’s dog in a park, as they defecated. These animals all excrete cylinder-shaped faeces like humans, and the duration of defecation remained constant (Soft Matter, doi.org/b6fg). That consistency across animals is down to a few things. First, the length of faecal pieces was five times as long as the diameter of the rectum in each of the animals. Yang also found that the normal, low-level pressure animals apply to push through a bowel movement is constant, and unrelated to a creature’s body mass. This means
SOURCE: doi.org/10.1016/j.epsl.2017.03.036 SOURCE: doi.org/10.1016/j.epsl.2017.03.036
Colin Barras
stacked sheets of rigid material such as glass. These experiments show that when a runnier fluid is squirted into a more viscous one, it forms an intricate radial pattern of branches, or fingers. The work even inspired the logo of the BP Institute at the university. “I’ve walked past the logo every day for about 15 years,” says White. Now White and his student Charlotte Schoonman think the plume is behaving just like the fluids in the lab experiments, but on a much grander scale. About 100 kilometres below Earth’s surface lies the asthenosphere, a zone of relatively free-flowing rock
that, whether it’s a human or a mouse, the pressure on normal excrement is the same. This is similar to her previous finding that mammals take the same amount of time to empty their bladders. The final piece of this puzzle is the crucial mucus layer in the colon. Cylindrical faeces aren’t squeezed through a nozzle like a toothpaste tube. “It’s more like a plug that just goes through a chute,” says Yang. Larger animals have longer faeces and a longer rectum, but they have thicker
“Without a slick mucus layer, a human applying no pressure would take 500 days to void their bowels”
G_Iceland_plume_060517 G_Iceland_plume_060517
held between two horizontal layers of stiffer rock. Iceland’s plume, they say, injects hot, runny rock into this layer that then spreads out horizontally into fingers. Other plumes don’t form such tendrils, says White, because the rock within them is not sufficiently hot and runny, or injected with enough force (Earth and Planetary Science Letters, doi.org/b6h9). The fingers on the Icelandic plume’s eastern side seem to stretch surprisingly far, one reaching Scotland some 1000 kilometres away, and another one further still, to Norway. The hot fingers may even help to explain why Scotland and western Norway lie above sea level. Earth’s crust beneath these areas is unusually thin, meaning that both regions should in theory be below sea level. “Something else must be going on to explain why they’re not under water,” says White. “And that something else is the hot fingers.” This is because the hot rock is relatively buoyant, which could compensate for the thinness of the crust, pushing it up. Taras Gerya at the Swiss Federal Institute of Technology in Zurich thinks that the model makes sense. “It seems realistic to me,” he says. n
mucus, which makes the faeces accelerate faster – so they travel a longer distance in the same amount of time. Constipation happens when that mucus is absorbed by the faeces. Without this slick layer, a human applying no pressure at all would take 500 days to void their bowels, Yang says. “It would be 6 hours if you apply maximum pressure,” she says. The team fed their observations into a mathematical model that can predict defecation times for digestive system problems. “If it’s taking far longer than 12 seconds, I’d say you should go see someone about it,” says Yang. “But you can’t count the newspaper time.” Chelsea Whyte n
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Scotland floats on a hot starry plume THE plume of hot rock that sits beneath Iceland has long-reaching fingers – two of which stretch all the way to Scotland and Norway. This perhaps explains why the breathtaking scenery of areas such as the Scottish Highlands isn’t submerged beneath the waves. Mantle plumes are like chimneys that transport hot, buoyant rock from deep inside Earth. When they break through to the surface, the volcanic activity they generate can fuel the formation of new islands, such as the Hawaiian archipelago. Iceland also owes its existence to a mantle plume – and seismic maps of Earth’s interior suggest that this plume doesn’t have the typical circular outline. “It’s far more irregular,” says Nicky White at the University of Cambridge. In fact, it looks a bit like flower petals or a star shape on top of a chimney of rising hot rock (see diagram, right). But why or how that irregularity arises has
Most mammals take 12 seconds to defecate EVERYONE poops, and we all take about the same amount of time to do it. A study of the hydrodynamics of defecation finds that all mammals producing faeces similar to ours take 12 seconds on average to relieve themselves. “The smell of body waste attracts predators, which is dangerous for animals. If they stay longer doing their thing, they’re exposing themselves and risking being discovered,” says Patricia Yang, a mechanical engineer 16 | NewScientist | 6 May 2017
remained a mystery until now. When White saw one particular map of the plume’s outline below Earth’s surface, it suddenly dawned on him how it might have gained its irregular shape. He recalled experiments by some of his colleagues in Cambridge. They have looked at how fluids with different viscosities mix in the confined, almost twodimensional gap between two
Europe’s splattering plume Europe’s splattering plume When hot rock rising up below Iceland reaches the asthenosphere,
100km below surface, spreads out to form long, runny fingers, When hot rockEarth’s rising up belowitIceland reaches the asthenosphere, two of which Scotland and Norwayout to form long, runny fingers, 100km belowreach Earth’s surface, it spreads two of which reach Scotland and Norway FINGERS FINGERS
MANTLE PLUME MANTLE PLUME Idealised shape of the plumeshape splatter Idealised of the plume splatter
at the Georgia Institute of Technology in Atlanta. Yang and colleagues filmed elephants, pandas and warthogs at a local zoo, and one team member’s dog in a park, as they defecated. These animals all excrete cylinder-shaped faeces like humans, and the duration of defecation remained constant (Soft Matter, doi.org/b6fg). That consistency across animals is down to a few things. First, the length of faecal pieces was five times as long as the diameter of the rectum in each of the animals. Yang also found that the normal, low-level pressure animals apply to push through a bowel movement is constant, and unrelated to a creature’s body mass. This means
SOURCE: doi.org/10.1016/j.epsl.2017.03.036 SOURCE: doi.org/10.1016/j.epsl.2017.03.036
Colin Barras
stacked sheets of rigid material such as glass. These experiments show that when a runnier fluid is squirted into a more viscous one, it forms an intricate radial pattern of branches, or fingers. The work even inspired the logo of the BP Institute at the university. “I’ve walked past the logo every day for about 15 years,” says White. Now White and his student Charlotte Schoonman think the plume is behaving just like the fluids in the lab experiments, but on a much grander scale. About 100 kilometres below Earth’s surface lies the asthenosphere, a zone of relatively free-flowing rock
that, whether it’s a human or a mouse, the pressure on normal excrement is the same. This is similar to her previous finding that mammals take the same amount of time to empty their bladders. The final piece of this puzzle is the crucial mucus layer in the colon. Cylindrical faeces aren’t squeezed through a nozzle like a toothpaste tube. “It’s more like a plug that just goes through a chute,” says Yang. Larger animals have longer faeces and a longer rectum, but they have thicker
“Without a slick mucus layer, a human applying no pressure would take 500 days to void their bowels”
G_Iceland_plume_060517 G_Iceland_plume_060517
held between two horizontal layers of stiffer rock. Iceland’s plume, they say, injects hot, runny rock into this layer that then spreads out horizontally into fingers. Other plumes don’t form such tendrils, says White, because the rock within them is not sufficiently hot and runny, or injected with enough force (Earth and Planetary Science Letters, doi.org/b6h9). The fingers on the Icelandic plume’s eastern side seem to stretch surprisingly far, one reaching Scotland some 1000 kilometres away, and another one further still, to Norway. The hot fingers may even help to explain why Scotland and western Norway lie above sea level. Earth’s crust beneath these areas is unusually thin, meaning that both regions should in theory be below sea level. “Something else must be going on to explain why they’re not under water,” says White. “And that something else is the hot fingers.” This is because the hot rock is relatively buoyant, which could compensate for the thinness of the crust, pushing it up. Taras Gerya at the Swiss Federal Institute of Technology in Zurich thinks that the model makes sense. “It seems realistic to me,” he says. n
mucus, which makes the faeces accelerate faster – so they travel a longer distance in the same amount of time. Constipation happens when that mucus is absorbed by the faeces. Without this slick layer, a human applying no pressure at all would take 500 days to void their bowels, Yang says. “It would be 6 hours if you apply maximum pressure,” she says. The team fed their observations into a mathematical model that can predict defecation times for digestive system problems. “If it’s taking far longer than 12 seconds, I’d say you should go see someone about it,” says Yang. “But you can’t count the newspaper time.” Chelsea Whyte n
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