Tenacity of Life
A final point regarding the prokaryotes relates to their tenacity and
ability to survive for long periods of time.
There are many examples of bacteria being revived after long term
storage, but perhaps none any more dramatic than those from the Antarctic
permafrost, where soils that have been permanently frozen for 3 million years
or more have yielded copious numbers of living bacteria. Dr. David Gillichinsky and his colleagues
from Puschino, Russia, have been drilling in such sites for many years now, and
a number of organisms have been “revived” from their carefully collected
samples. It is not unusual to find 106
to 107 (1 to 10 million) viable bacteria from each gram of
permafrost. These are not cold loving (psychrophilic)
bacteria that have adapted to these freezing conditions, but simply mesophilic
organisms that have been trapped within this icy storage facility for millions
of years.
So, as we are poised to proceed to other celestial bodies in search of
life, we find that our definition of habitability is quite different from what
we adhered to just a few years ago. In
response to this, we must: a) consider that the physical and chemical
conditions tolerant to life are broader than we once thought; b) examine the
potential energy sources available and look carefully for life forms utilizing
any such energy; and, c) be prepared for subtle, single-celled life that may
not be obvious at first glance, even looking in places where life might have
been preserved as dormant forms.
Contributed by: Dr. Kenneth Nealson
|
