9 Facts About Human Decomposition

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From rotting corpses crawling with maggots to oozing bodies emitting stomach-churning stenches, the decaying human body is the stuff of nightmares, horror movies, and crime dramas. We're both fascinated and repelled by decomposition, which has given rise to many myths and urban legends. (No, hair and nails don't grow after death, and corpses never sit up on mortuary tables.) Here are nine fascinating facts that demystify how we transition from flesh to bone to dust.

1. DECOMPOSITION STARTS ALMOST IMMEDIATELY AFTER DEATH.

It takes approximately four minutes from the moment a person has breathed their last for the shortage of oxygen in their body to kick off a series of events happening at the microscopic level: The levels of carbon dioxide and acidity rise in the bloodstream, and toxic wastes build up, poisoning the cells. Then, enzymes within cells begin to eat away at them. Organs with high concentrations of enzymes and water, such as the liver and the brain, are ground zero for this process.

One of the first visible signs of death is when the eyes cloud over, a result of fluids and oxygen no longer flowing to the corneas. That can begin within 10 minutes [PDF] of death.

2. THERE ARE FIVE PHASES OF DECOMPOSITION.

The first phase is called fresh. It's characterized by cell autolysis, "or self-digestion": The cells burst open due to the work of enzymes, and fluids leak out. Fluid-filled blisters emerge on the skin, which slips easily off the body in large sheets.

Meanwhile, resident anaerobic bacteria in the gut begin to break down cells, beginning the second phase of decomposition: bloat. As these microbes work away, gases begin to accumulate in the intestines, and the surrounding tissues expand. The gases react with hemoglobin, a protein found in red blood cells, producing a green pigment in the veins ("marbling"), and the skin turns green, then black.

During active decomposition, the third phase, tissues begin to liquefy and decomposition fluids seep out through orifices. According to Dawnie Wolfe Steadman, director of the Forensic Anthropology Center at the University of Tennessee, Knoxville, the loss of tissue mass is the chiefly the work of fly maggots—which feast on tissues—and bacteria.

Advanced decomposition is when most soft tissues are gone, whatever skin is left has turned dry and leathery, and the skeleton is visible, thanks to the handiwork of yet more bugs. "While the fly maggots no longer have much to feed on, other insects such as beetles come," Steadman says. "They are capable of breaking down the tougher soft tissues, like tendons, ligaments, and even cartilage."

Skeletal decay is the end of the decomposition process. A variety of factors result in the breakdown or fragmentation of bones. Acidic soil, for example, dissolves an inorganic mineral compound called hydroxylapatite—a mix of calcium and phosphate—that accounts for 70 percent of our bone material [PDF]. Bones can also disintegrate when they are subjected to a variety of physical forces, including being gnawed on by scavengers or being slowly eroded by the flow of water.

How long each of the above stages lasts depends on factors such as temperature, burial conditions, and the presence of microbes, insects, and scavengers. Active decomposition in particular is greatly influenced by the temperature; flies lay their eggs in warmer months, so decomposition tends to be slower in colder temperatures. Bones generally begin to bleach within the first year, and algae and moss may grow on their surface. Large cracks tend to form after about a decade.

3. RIGOR MORTIS IS ONLY TEMPORARY.

Fans of shows like Law & Order: SVU are likely to be familiar with rigor mortis, or the stiffening of the body’s muscles following death. It begins within two to six hours, originating in the face and neck and spreading outwards toward the limbs. Rigor mortis is the result of the two types of fibers in our muscle cells—actin and myosin—becoming tightly linked by chemical bonds that develop in response to lower pH levels in the cells, creating inflexibility [PDF]. But this rigidity goes away within 1 to 3.5 days, as the bonds between the muscle fibers break and the muscles relax, once again starting with the face. As this happens, the body can release feces and urine.

Rigor mortis occurs more quickly and persists longer in cooler temperatures than in warmer ones; according to one study, rigor lasted for 10 days in corpses refrigerated at 39°F in a mortuary. What happens right before death can influence rigor mortis too: A high fever will shorten how long it lasts, while vigorous physical activity will cause it to set in sooner. These effects are likely caused by a drop in the levels of the chemical ATP (adenosine triphosphate), an energy driver in cells, and increased amounts of lactic acid, which lower the pH in muscle cells.

4. DECOMPOSITION DOESN'T SMELL AS BAD AS YOU'D EXPECT.

“People think bodies always smell awful,” says Melissa Connor, director of the Forensic Investigation Research Station at Colorado Mesa University. “But while there are a few times and phases [where the] remains are odiferous, for the most part, the smell is not overpowering.”

Malodorous gases build through the bloat phase, but the smells lessen as decomposition progresses. According to Connor, in the summer, a corpse can pass through the odiferous stages in 10 days or less.

A mix of gases is responsible for the “sickly sweet” stench of death. Of these, putrescine and cadaverine—produced when bacteria break down the amino acids ornithine and lysine, respectively—emit distinctive noxious odors. These gases can be absorbed through the skin and compete with or displace oxygen—a potential health risk for people working with decomposing bodies in closed environments, such as underneath a house or in a well shaft. A recent study suggests that putrescine may act as a warning signal that death is near, triggering a “flight-or-fight” response.

5. DECOMPOSITION CAN SOMETIMES CREATE "SOAPY" CORPSES.

Another stinky by-product of decomposition is a waxy substance called adipocere. It's formed from fat under wet conditions through a process called saponification (the same basic chemical reaction by which soaps are made from fats). Fresh adipocere smells like ammonia, but over time, adipocere dries out and the odor disappears. Philadelphia’s Mütter Museum has a specimen of a corpse encased in adipocere known as the Soap Lady, who was exhumed in 1875 from a city cemetery. The Smithsonian has a male counterpart: Soapman, who was also found in Philadelphia in 1875 during the construction of a train depot. He died around 1800.

6. THE 'NECROBIOME' COULD HELP US DETERMINE TIME OF DEATH MORE ACCURATELY.

Forensic entomologists use insects to infer time of death, but there are other potential biological clues. According to Steadman, forensic scientists are researching how different species of bacteria can influence decomposition, and if bacteria can help identify individuals.

"Some researchers are looking at the necrobiome—or all the little bacteria and fungi that inhabit a corpse—and seeing if changes in the necrobiome can inform time of death," Connor says. By knowing which strains of bacteria and other microbes are present at each phase of decomposition, scientists can put together a microbial clock to help estimate the time since death. Some of these microbes come from our own microbiome; others come from the surrounding soil, or are carried to the body by flies, other insects, and scavengers.

7. WITHOUT BUGS OR BACTERIA, DECOMPOSITION CAN SLOW WAY, WAY DOWN …

In December 1977, in Franklin, Tennessee, the Williamson County Sheriff was called to an antebellum estate called Two Rivers. The owners had reported a disturbance in the small graveyard attached to the estate. There, the sheriff’s department found a headless male corpse dressed in formal wear atop the broken coffin of a Confederate lieutenant colonel named William Shy, who had died in 1864. Forensic anthropologist William Bass was asked to examine the body.

In his book Death’s Acre, Bass writes that the corpse had been preserved in the early stages of decomposition; the "flesh was still pink," he notes. He estimated the man had been dead a year at most. But some things didn't add up, which puzzled Bass. The style of clothing was dated and the shoes were made of old materials. The corpse’s head was later found in the coffin, and the teeth had not seen modern dentistry. All of this led Bass to suspect that the body was in fact Shy’s.

Turns out he was right the second time around. Shy's corpse had been unceremoniously yanked out of his resting place by grave robbers. The 113-year-old body was so well-preserved because it was embalmed—which slows decomposition (by how much depends on the embalming process)—and because the cast-iron coffin was hermetically sealed, keeping out any insects and microbes that would have pushed decomposition beyond the early stages.

More recently, in May 2016, an airtight metal casket was unearthed in a backyard in San Francisco. The home had been built on the site of a cemetery. Inside the casket was the well-preserved body of a toddler, Edith Cook, who had died in 1876. News reports don’t explicitly state whether Edith was embalmed, but old ads from the casket’s manufacturers boast that it offered “perfect protection from water and vermin.”

Still, cast-iron coffins aren't decomposition-proof: In other cases, they've exploded due to bloat-stage gases. This gas buildup has been a problem for some modern "protective" or "sealer" caskets too.

8. … AND ENVIRONMENTAL CONDITIONS CAN ALTER DECOMPOSITION.

Certain environmental conditions are ideal for preserving bodies and creating natural mummies—which are unique because the skin survives active decomposition.

A combination of low oxygen, highly acidic water, and cool temperatures in European peat bogs turns corpses into bog bodies. While the acidic water breaks down bones, tannins in the peat and the lack of oxygen preserve skin—every expression, wrinkle, and fingerprint—with astonishing detail. Famous examples include the Tollund Man and Lindow Man.

La Doncella, or “The Maiden,” is an ancient Inca teenager who was left to die in the Andes Mountains in Argentina as a part of a ritual sacrifice. She was found in 1999, head down, appearing to be asleep. Though she died more than 500 years ago, her hair, skin, and clothing are all almost perfectly preserved. The high altitude, low temperatures, and low oxygen level account for La Doncella’s condition.

Another example of the preservative powers of the mountains is Ötzi, a natural mummy of a man who died about 5300 years ago. He was discovered in 1991 in Ötztal Valley Alps and has been preserved almost in his entirety. Though the glacier ice dehydrated his body, his skin, other tissues, organs and bones remain in great shape.

9. DISEASES THAT KILL THEIR HUMAN HOSTS CAN SURVIVE DECOMPOSITION.

A number of disease-causing viruses can hang around even after death. The Ebola virus is particularly contagious even after a person has died: It remains in their blood and other bodily fluids. Any contact with broken skin or the mucous membrane (which lines the nose, mouth, and other body cavities) of a healthy person is enough to pass on the infection. For this reason, the World Health Organization recommends that infected bodies be buried quickly and safely, with everyone handling the body wearing protective gear and the body buried in a coffin in the ground. The virus has been shown to persist in dead primates for up to a week.

Norovirus (the stomach flu) can also spread in a manner similar to Ebola, and it is possible to catch influenza from the infected mucus of a dead person. The smallpox virus remains in the scabs of a dead person for as long as a century—but at least it's not contagious from the dead to living.

New Study Reveals 'Hyper-Alarming' Decline of Rainforest Insect Populations

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Climate change is decimating yet another vital part of the world's ecosystem, according to a startling new paper. Rainforest insects are dying off at alarming rates, according to a new study spotted by the The Washington Post. In turn, the animals that feed off those insects are decreasing, too.

In the study, published in Proceedings of the National Academy of Sciences, a pair of scientists from the Rensselaer Polytechnic University in New York and the National Autonomous University of Mexico studied populations of rainforest arthropods (an invertebrate classification that includes insects and spiders) in the El Yunque National Forest in Puerto Rico. They compared the number of insects lead author Bradford Lister found on trips in 1976 and 1977 with the number he and co-author Andres Garcia found on trips they took between 2011 and 2013.

Lister and Garcia used nets and sticky traps to collect insects on the ground and several feet above the ground in the forest canopy. They dried these captured bugs and measured the mass of their haul against the mass of insects found in the 1970s, finding that the modern net sweeps captured only an eighth to a fourth of the insects captured in the '70s. The mass of insects captured by sticky traps on the ground declined by 30 to 60 times what they were a few decades ago. They also tracked populations of lizards, frogs, and birds that live off those rainforest insects, finding that those populations had declined significantly, too, at levels not seen in other rainforest animals that don't rely on insects for food.

Tropical insects are particularly vulnerable to climatic changes, since they can't regulate their body temperature. During the time of the study, average maximum temperatures in El Yunque rose by almost 4°F (2°C). The warming climate is "the major driver" of this decline in arthropod populations, the study authors write, triggering a collapse of the forest food chain.

The paper has other scientists worried. "This is one of the most disturbing articles I have ever read," University of Connecticut entomologist David Wagner, who wasn't involved in the research, told The Washington Post, calling the results "hyper-alarming." Other studies of insect populations have found similarly dire results, including significant declines in butterflies, moths, bees, and other species. One recent study found that Germany's flying insect populations had decreased by as much as 75 percent in the last three decades. Scientists don't always attribute those population losses directly to warmer temperatures (habitat loss, pesticide use, droughts, and other factors might play a role), but it’s clear that insect populations are facing grave threats from the modern world.

Not all insect species will be equally affected by climate change, though. While we may see a sharp drop in the populations of tropical insects, scientists project that the number of insects in other regions will rise—leading to a sharp increase in crop-eating pests in some parts of the world and broadening mosquitos' geographical range.

[h/t The Washington Post]

This 'Time-Traveling Illusion' Is Designed to Trick Your Brain

A team of researchers from the California Institute of Technology (Caltech) have designed an illusion that might trick your brain into seeing things that aren’t there, the New Atlas reports.

Dubbed the Illusory Rabbit, it provides instructions that are simple enough to follow. Start playing the YouTube video below and look at the cross in the middle of the screen while also watching for flashes that appear at the bottom of the screen. Most importantly, you’ll want to add up the number of flashes you see throughout the video. (And make sure your volume is up.)

We don’t want to spoil the fun, so before we explain the science of how it works, check out the video and try it for yourself.

Did you see three flashes paired with three beeps? You’re not alone. This is due to a phenomenon called postdiction, which is a little like the opposite of prediction. According to a paper outlining these findings in the journal PLOS ONE, postdiction occurs when the brain processes information retroactively [PDF]. This occurs in such a way that our perception of earlier events is altered by stimuli that come later. In this case, you might think you missed the flash paired with the second of the three beeps, so your mind goes back and tries to make sense of the missing information. That's why you may see an “illusory flash” in the middle of the screen, sandwiched between the two real flashes.

For this reason, the researchers call the mind trick a “time-traveling illusion across multiple senses” (in this case, vision and hearing). It’s successful because the beeps and flashes occur so rapidly—in less than one-fifth of a second. The senses essentially get confused, and the brain tries to fill in the gaps retroactively.

"Illusions are a really interesting window into the brain," the paper’s first author, Noelle Stiles, said in a statement. "By investigating illusions, we can study the brain's decision-making process.” Researchers wanted to find out how the brain “determines reality” when a couple of your senses (in this case, sight and hearing) are bombarded with noisy and conflicting information. When the brain isn’t sure of what’s going on, it essentially makes up information.

“The brain uses assumptions about the environment to solve this problem,” Stiles said. “When these assumptions happen to be wrong, illusions can occur as the brain tries to make the best sense of a confusing situation. We can use these illusions to unveil the underlying inferences that the brain makes."

[h/t New Atlas]

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