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 decompositon

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.

Even cremation, the second most common burial practice in the world,

comes with a high cost.

As for the question of running out of space,

the issue isn't so much about total land in the world

as it is that large populations cluster together within cities.

Most of the big cities in the world

may run out of suitable burial grounds within a century.

For London, it's even sooner.

That may happen by 2035.

So are there alternatives to traditional burials

that might help with the space issue?

In some countries, skyscraper cemeteries enable vertical burials.

Some options focus on the body's relationship with the environment.

Promession, for example, freeze-dries and pulverizes the body,

creating a powder that can turn into compost

when mixed with oxygen and water.

There are also green burials that use special materials,

such as biodegradable caskets,

urns that sprout trees,

and burial suits that grow mushrooms.

Eternal reefs take that concept to the depths of the ocean

using a mixture of ashes and cement to create marine habitats for sea life.

Death is an inevitable part of the human condition, but how we treat bodies and burials continues to evolve.

We may each have different spiritual,

religious,

or practical approaches to dying,

but the ever-increasing demand for burial space

might give us a push to be creative

about where our bodies go after the final stages of life.