QUESTION:
If terraforming was ever undertaken, what is the risk of awakening a
dormant organism and causing the contamination of Earth?
 
ANSWER from Geoff Briggs on April 29, 1997:
Any serious attempts to terraform Mars are probably be in the quite distant
future -- 100+ years.  By that time we will surely have characterized Mars
including any extant life.  In fact, learning as much as we can about
possible extinct and extant life is a principal purpose in exploring Mars.
So we expect to explore all likely sites (i.e. those where there may be
liquid water) -- thermal springs, deep drilled holes down to aquifers at
several mile depths, the base of the permanent polar caps where there could
be melted water, and deep caves.

If we encounter extant life (in rocks or perhaps in water from depth) we
will need to treat it very carefully and place samples in strict quarantine
until we understand any possible threat to astronauts or to the terrestrial
ecosphere.  By the time that you refer to, we should fully understand what
we are dealing with (at the molecular biology level) and so there should be
no new threat from previously dormant organisms.  In the nearer term --
while we are exploring Mars and not yet knowing what to expect -- there are
indeed plantary protection concerns that NASA is addressing seriously.
NASA has enlisted the help of the National Academy of Sciences to get their
recommendations about quarantine facilities and to ensure that we take all
proper precautions.

Having said this, it should be pointed out that scientists consider the
potential threat of putative martian organisms to be very small (for a
variety of reasons).  But we cannot say it is zero.  Note that a lot of
martian rocks have been delivered to Eaarth as meteorites and that quite
likely Earth is being continuously "contaminated" by any martian life --
since billions of years ago.  It has been estimated that about 100 lb of
martian meteorites falls on Earth every year.