|Why is life possible on Earth?|
|Question Date: 2019-02-01|
Life is possible on Earth because Earth has the
particular characteristics and substances that are
required by all known life forms. There are a few
generally agreed upon. One of the main
requirements is a liquid where molecules can
react. On Earth, this is water.
Water can dissolve a wide variety of
substances which enables the interactions of
myriad chemical species that interact to carry out
the processes required by life forms. However,
other liquids are also (hypothetical)
possibilities, such as ammonia or various
hydrocarbons like ethane and propane. Another
requirement is an energy source. Most
energy for Earth comes from
our sun. However, plenty of life exists in
deep ocean vents without energy from the sun
see also here ). There are also
some chemicals which seem to be the
basis for all organisms: carbon, hydrogen,
nitrogen, oxygen, and sulfur (and sort of
phosphorus, but an exception has been found).
These combine to form the proteins and nucleic
acids which make up the genetic code of living
things and are present on Earth in sufficient
quantities and availability. These elements are
quite common elsewhere in the universe too though,
so don't expect this to limit life. There are a
few other features of Earth which make it
suitable for life, such as being far enough from
dangerous galactic neighbors (e.g. stars emitting
frequent gamma rays, large stars that might go
supernova); Earth's inner core is molten metal,
which generates a
magnetic field to protect life from events like
solar flares and solar wind; and also a moon that
is large enough to stabilize the planet
which then stabilizes the climate and prevents
dramatic, dangerous variations.
There are a plethora of
hypothetical biochemistries which may
eventually prove suitable to sustain life. These
hypothetical forms of biochemistry and the
characteristics in the first paragraph are based
on life that is known to exist though. As pointed
ScienceLine here, biologists define life by
meeting certain basic criteria. None of them are
"needs water" or "based on carbon" though. With
this in mind, some thing could meet the biological
definition of life and not need any of what is
listed in the previous sections. As given at the
beginning, life is possible on Earth because Earth
happens to have the stuff that known life
needs. But keep in mind that unknown life
could be very different.
The origin of life is one of the great unsolved
questions in science. We know life is possible on
Earth, because we see it all around us. We
don't know if life is possible on other planets.
Here's one way to think about life starting on earth:
The origin of life is an example of ‘the whole
is greater than the sum of its parts.’ Think
of hydrogen + oxygen = water [H2O],
which is so incredibly different from hydrogen gas
and oxygen gas. Think of a functioning car vs the
parts that go into it but don’t do anything useful
by themselves. Life is a very complex example
of a whole [life] that is greater than the sum of
Here are links to work I've done about the
origin of life:
Possible Origin of Life between the Sheets of Mica
Granny Says Life Evolved Between the Mica Sheets.
One of my books on the same topic:
How Did Life Start? Maybe Like This
This is a question under active research. We have
some theories for how life started, and what we
know is that life required water and some basic
building blocks made of atoms of carbon, nitrogen,
oxygen, and so on. However, from a scientifically
philosophical point of view, we do not really know
why life is possible on Earth. Part of the reason
is that we simply do not have a lot of data about
life. In other words, we only know some things
about life on Earth, under very few sets of
chemical and biological conditions, but we don't
know about life in other places in the universe or
even in our solar system. This is part of the
reason that we are seeking ways to study ice,
water, and biological molecules on planets, moons,
and asteroids in our own system - to understand
what makes the Earth so suitable for life, and to
get some answers for the questions, "Are there
other conditions under which life is possible?
If so, what are these conditions and what does
living organisms look like under these
It’s pretty crazy that life is possible on Earth.
There are many factors, and they all work together
perfectly so that you and I can live comfortably
on Earth’s surface. There are 6 main reasons:
1) We are just the right distance from the sun.
Any farther away (like Saturn or Jupiter) and our
water would all be frozen. If we were any closer
(like Mercury), our water would all evaporate!
2) Speaking of our sun, it’s just the perfect
size. Really big stars tend to burn really hot and
don’t live very long, and smaller stars are
usually unstable and blast their planets with
bursts of deadly radiation.
3) Earth is also special because it is surrounded
by a giant magnetic field that protects us from
4) We are also surrounded by this amazing thing
called the ozone layer that is really high in the
sky. Without it, we wouldn’t be protected by all
the dangerous and deadly radiation in space.
5) Our moon is also important. Earth is
tilted and spins at an angle, so it wobbles a
little bit. However, our moon stabilizes this
wobble and keeps our climate and weather stable!
6) Finally, our solar system is nestled nicely
between the major arms of our galaxy (the Milky
Way). Our solar system is far enough away from
other ones so that they don’t tug and pull on ours
and that keeps us safe from collapsing.
It’s pretty amazing that all of these factors work
together to create a world we can live in.
Life as we know it is possible on Earth because
Earth exists within the range of conditions that
life can inhabit. In general, this means that
Earth has liquid water, as well as sources of
energy, either through geologic activity or
through sunlight, for living things to use this
energy to grow and reproduce. It is possible that
there are other forms of life in the universe that
we have not yet discovered and that could not
exist on Earth, however. Similarly, if these other
forms of life exist, then Earth-like life probably
could not exist where these other life-forms do.
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