The abundance of activity leading to a body’s decomposition after death

In the time it takes to read this sentence, two to four people will have died. Once their heart stops beating, the first issue most of their cells will face will be a lack of fresh oxygen. This kills brain cells within minutes, which basically puts an end to consciousness as we understand it. It’s not, however, the end of a body’s activity, as different tissues survive different lengths of time. It will actually take up to a couple of days for every cell to finally expire, at which point a variety of processes will have taken place, both inside and outside the deceased. The weird thing is that up until a body has been reduced to bone, what’s left of the flesh is very likely to smell like… gasoline?

The first 48 hours after someone dies is actually packed with action, but not all of it is visible. Muscles tighten with rigor mortis, then later relax. Blood is left subjected to gravity, and pools in whatever part of the body is pointed at the ground. The pancreas is digested by its own enzymes, but a lot of this isn’t obvious from first glance. Bodies as this stage of decomposition are reported to smell like almonds, tallow, mothballs and yep, gasoline.

Mobilized mRNA

On a cellular level, scientists have discovered that some of the cells are not only still alive, but still working. Large amounts of messenger RNA (mRNA), which is the biological middleman a gene relies on to get a cell to produce specific proteins, have been found in fish and mouse brains and livers up to four days after death. In some cases, the genes weren’t simply carrying on with their daily routine, but instead seemed to have been reactivated at the time of death. These include genes that are generally inert after birth, instigate inflammation responses or others that have connections to cancer. A definitive purpose for this activity isn’t clear, and it may turn out that these genes are activated only because the other genes that had been keeping them quiet have already quit.

Bustling bacteria

As more human cells, die, bacteria in what’s being called the necrobiome start to dominate the body. The dramatic shift in a corpse’s microbial ecology hasn’t been fully mapped out yet, but a few key points are hard to miss. Many of the bacteria start (or continue) producing hydrogen sulfide and methane, both of which build up in spaces that now lack the muscles to help vent excess gas. As the corpse becomes visibly bloated, it takes on smells of garlic, various bodily fluids that are beginning to leak, and gasoline. Eventually, some cavity will rupture, at which point a second wave like Clostridia, which don’t like oxygen, will start growing more in remaining tissues.

Food for flies

Unless a body has been carefully isolated from the natural world, many of these processes will be competing for time against third party insects and bacteria. Flies can be sustained through their entire life-cycle on a corpse, since the decaying flesh can provide both food and shelter for eggs, larvae and pupae. This may sound gross, and the accompanying smells of fruit, molasses, boiled cabbage and gasoline probably don’t help, but these hungry insects are actually amazingly efficient at reclaiming resources for an ecosystem, passing them along to larger animals if the flies get eaten later on. In just seven days, up to 60 percent of a human body can be transformed from dead cells into live bugs, although if you want to really polish things off, you need to call in some (amazing) dermestid beetles.

Once all the soft tissue has been removed, decomposition slows down considerably. Those tissues can become mummified or in some cases, fossilized, but bones’ durability can make them last for much longer than any other anatomy. And importantly, the gasoline smell usually gets downgraded to paint thinner, nail polish, or maybe even mint.

Source: How Body Farms Work by Tom Scheve, How Stuff Works