|Is fire alive? It moves, it feeds on oxygen, but
it doesn't think or know where it is moving.
|Question Date: 2003-05-06|
When sitting and watching a fire, it is easy to
get the idea that it is alive. It moves
dynamically, dancing and sending sparks. It is
able to spread across a surface, and move about
from combustible object to combustible object. It
consumes such materials as wood, converting them
into ash and other byproducts. It needs oxygen,
as though it were breathing. However, fire is
most definitely not alive.
In fact, none of
these criteria prove that something is
Oftentimes we think that all life
requires oxygen. However, there are many bacteria
(called anaerobic bacteria) which do not need
oxygen at all! They live down in the soil, under
oceans and lakes, and in other areas. To many of
them, oxygen is a poison! Yet they are definitely
alive. So clearly whether or not something needs
oxygen does not show if it is
Consciousness as we think of it is
probably not a good determinant for life either.
It is highly unlikely that bacteria, fungi,
plants, and other organisms think, since they lack
a brain or nerves. Yet they are definitely alive.
Therefore whether or not something thinks
does not show that if is alive. This is the same
for movement, because not all living things move--
in fact, many living things move a lot less than
fire! And many non-living things move, such as
the wind or a car.
In order for something
to be considered alive it must have several
characteristics and abilities, such as metabolism,
growth, reproduction, and response to stimuli or
adaptation to the environment. How does fire
stack up to these requirements?
certainly seems able to grow. A small campfire
can quickly grow to the level of a forest fire, so
yes, it seems to meet this criterion.
fire reproduce? Again, it seems able to! A
single spark can blow to a different location and
start a new fire. That might be considered
Fire is not alive, although it certainly seems to
have a mind of its own! The process of oxidation
is when substances react with the oxygen in the
air to make oxides (like rust on iron, is iron
oxide, and when your mom's silver tarnishes, that
is silver oxide). When things oxidize, they
release heat. Fire is just very rapid oxidation.
Heat rises, and makes currents of air that
circulate as the hot air rises - that is why
flames appear to dance and move around. Fire needs
oxygen to burn, and it needs fuel; for something
to "burst into flames" it needs to be at a high
enough temperature. Without any one of these
ingredients the fire won't burn.
A flame on
earth is in a gravitational field - that is why it
is thicker at the bottom. But a flame in the space
shuttle, in what they call "microgravity"(*)
environment is actually round! Pretty amazing -
imagine a "flame ball"! (* Actually there is
plenty of gravity up there - that is why the
shuttle stays in orbit - but it is in a state of
"free fall" around the earth so you _feel_
Biologists have fought a bit over the basic
definition of life, but all biologists would agree
that fire is not alive. Remember, not all living
things feed on oxygen (plants feed on carbon
dioxide), so that's not a good definition for
life. Not all living things move (again, plants do
not really move), so that's not a very good
definition of life. Not all living things "think",
either (plants do not think).What your question
really comes down to is how to define life. I've
tried to come up with some basic definitions of
-- For me, life can be defined by it's
most basic building block -- a cell. If something
does not contain at least one cell, it is not
alive. Fire does not contain cells.
things contain DNA and/or RNA, proteins which
contain the basic information cells use to
reproduce themselves. Fire does not contain DNA or
-- Living things are made of matter,
and you can weigh them. It may be hard to measure
the weight of one bacteria, but you get the point.
You cannot weigh fire, because it is simply
energy. It has no mass. Fire is energy given off
when matter burns. You can see it, but what you
see is merely light, so you cannot hold it.
Living things grow, and in growing they make new
matter, but it's not just any old matter.
is organization. All living things make the same
basic things: proteins, fats and carbohydrates,
for example. Fire cannot make proteins from the
oxygen and hydrogen and carbon it "feeds on", just
destroy proteins. This is a major difference.
-- Living things require nutrients and
water, and have complex ways of finding and using
the things in their external environment that they
need. Living things also have ways of sensing and
responding to threat or attack.
That's a great question because fire does have
some things in common with living things. It needs
fuel and oxygen. It can grow. It "reproduces" to
make more fires.
But fire is also different
from living things. For one thing, it is not made
of cells. All living things are made of cells.
Also, when fire "reproduces," no information
is passed on. In living things, DNA carries
information from one generation to another. All
living things are adapted to where and how they
live by evolution, which changes DNA over time.
Fire is basically the same every time. It may be
bigger or smaller, hotter or less hot, or moving
differently, but that's all because of the
conditions right now, not because of information
it inherited in DNA.
Another difference is that
all living things come from other living things.
One-celled living things divide to make two new
one-celled things. Eggs, spores, seeds, babies,
and growing new individuals from parts of their
"parents" are all ways to reproduce new life from
live things. Fire can come from a match, rubbing
sticks together, a spark, or other things that are
So fire is a great example of
something that has some characteristics of life.
Thinking about ideas like this helps us to really
figure out what we mean by life.
If you could
make robots that made other robots, would they be
According to Hickman, Roberts, and Larson (1997),
any living organism will meet the following seven
basic properties of life:
uniqueness. Living systems demonstrate a unique
and complex molecular organization.
Complexity and hierarchical organization. Living
systems demonstrate a unique and complex
Living systems can reproduce themselves.
Possession of a genetic program. A genetic program
provides fidelity of inheritance.
Metabolism. Living organisms maintain themselves
by obtaining nutrients from their environments.
6) Development. All organisms pass through a
characteristic life cycle.
reaction. All animals interact with their
Fire is not alive. It does not
contain genetically inheritable information, and
arguably does not have a complex organization.
While it is true that fire feeds on oxygen and
moves it is lacking a very important feature to be
considered alive. In order to be considered alive
you have to be able to reproduce either sexually
or asexually at some point in your life. All
living things also contain a genome (DNA), that is
transferred to it's progeny (offspring)
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