Re: What is the long-term outlook for life on Earth and in our solar system?

Michelle:
     That is an interesting question.  I think that there are multiple 
answers to your question depending on how long you think "Long-Term" is, 
so I will set forth a few scenarios that explain some of the possibilities.
     Let me begin with the longest possible outlook, and that one, 
unfortunately, is completely terminal.  The longest time-frame imaginable 
is the end of the Universe itself.  This is proposed to occur in a 
multitude of ways, but regardless of how, it will spell the end for all things
in existence, every star, every planet, every nebula, every galaxy, 
and every atom will for all intents and purposes cease to exist.  
Fortunately for us the time frame for this catastrophic event is 
on the order of hundreds of billions of years.  This is a difficult number to 
comprehend, so let me put it into perspective...  Modern humans have been 
evolving for a scant 4 million years (plus or minus), and 100 billion is 
about 2,500 times as much time as humans have even been on the Earth.  It 
is 25 times more time than the Earth has even had something resembling 
life on it altogether.  So, as far as long term life goes, we are doomed...
     Second, and much more imperative to us (relative to the end of the 
Universe as we know it) is the demise of our solar system.  In about 5
billion years, our star, The Sun, will consume most of its available fuel
 and begin to die.  The death of our star is not instant, but
eventually it will turn into a cool, dim white dwarf which emits
very little energy. The take home message is that 
the death of our star will spell the end of the solar system as we know 
it.  Any planets themselves that survive the stellar event are doomed to 
drift and freeze as oversized asteroids in the darkness of space.  Without 
the light and heat of the Sun, our solar system could not sustain life, 
and in the absence of a star altogether, our solar system ceases to exist.
     Obviously, the time frame of these events is nearly unattainable, so 
there are certainly more current and noteworthy astronomical events that 
will probably occur within a more probable temporal frame.
     First, is the possibility of a collision of a planet, namely Earth, 
perhaps a moon of Jupiter harboring bacteria under the icecaps, with an 
extraterresterial body, such as an asteroid or comet.  In all likelihood, 
this event would eliminate most life found on that particular body in 
space.  These type of events are said to occur with a frequency of about 1 
every 100 million years or so, and putatively, the most recent major 
collision resulted in the demise of the dinosaurs and the rise of the 
mammals, ultimately humans and primates.  The chances of an event of this 
nature happening are 100%.  It is a question of when and where, not "if."  
Which is why, there are now groups of astronomers who look for objects 
that cross the Earth's orbit, and one of the pioneers of this "Sky-Watch" 
program was Carolyn Shoemaker, who with her late husband Eugene Shoemaker 
and David Levy discovered the comet fragments that collided into Jupiter 
in 1994.  So, there is certainly modern context for objects striking our 
planets and certainly every day, and more so during meteor showers you can 
catch a glimpse of what grains of sand look like as they re-enter the 
atmosphere and collide with the Earth.  
     Essentially the long-term prospects for life in the solar-system, 
particularly Earth, are that it will sustain life so long as the 
conditions that support that form of life exist.  At some point in time, 
the conditions will change, due to war, famine, global warming, or 
astronomical events, the delicate balance necesary to support certain 
types of life will cease to exist and an extinction or eradication will 
result.  
     I realize that this all seems quite morbid, but for a solar 
system/Universe ending event, the time frame is so long as to be forever 
Which means that we should look today to see where we can improve the 
current situation. With technology and controls to eliminate and reduce 
the much more likely causes of death and strife such as global warming, 
ozone depletion, famine, and impacts with space-bound objects.  Thank you 
for your question, you necessarily opened a large time-spanning can of 
worms, there is a lot to think about there.  Enjoy.

-Matt-   

[Moderator's note: more information about many of these topics, including
the end of the universe, the end of the Sun, and comet collisions can be found
in the Mad Sci archives.]