Since the dawn of humanity, an estimated 100.8 billion people have lived and died, a number that increases by about 0.8% of the world's population each year. What happens to all of those people's bodies after they die and will the planet eventually run out of burial space?
When a person's heart stops beating, the body passes through several stages before it begins decomposing. Within minutes after death, the blood begins settling in the lower-most parts of the body.
Usually, eight to twelve hours later, the skin in those areas is discolored by livor mortis, or post-mortem stain. And while at the moment of death the body's muscles relax completely in a condition called primary flaccidity, they stiffen about two to six hours later in what's known as rigor mortis.
This stiffening spreads through the muscles, and its speed can be affected by age, gender, and the surrounding environment. The body also changes temperature, usually cooling off to match its environment.
Next comes decomposition, the process by which bacteria and insects break apart the body. Many factors affect the rate of decomposition.
There is, however, a basic guide of the effect of the environment on decomposition called Casper's Law. It says that if all other factors are equal, a body exposed to air decomposes twice as fast as one immersed in water and eight times as fast as one buried in earth.
Soil acidity also greatly affects bone preservation. High-acidity soils with a pH of less than 5.3 will rapidly decompose bone, whereas in a neutral or basic soil with a pH of 7 or more, a skeleton can remain in relatively good condition for centuries.
Different cultures throughout history have developed unique approaches to burials. As far back as the first Neanderthal burials, death was accompanied by rituals, like the positioning, coloring, or decorating of corpses.
Traditional Christian burials decorate the body in dress, while in traditional Islam, a body is wrapped in a piece of ritual fabric with the face oriented toward Mecca. Traditional Hindus ceremonially burn the body, and Zoroastrians, followers of one of the oldest monotheistic religions, traditionally place bodies atop a tower to expose them to the Sun and scavenging birds. '
Before the Industrial Revolution, burials were simple and accessible. These days, with suitable burial land running out in high-population areas, purchasing private gravesites can be costly, and many people can't afford simple burials.
