Actually, this is not true. Organic compunds used to living at our
pressure and temp are very sensitive, but only because of the elements
their prtiens use to bind themselves together with. A protein molecule
is like a messed up ball of yarn, with energy bonds wherever the strands
cross. TO do its work as a protein, it must have a certain amount of
springiness to it to stay in solution, and must be able to be broken
apart with little energy input. Too much energy input, and the molecule
will break apart and precipitate out of solution, which is how egg
whites get white when you boil them. Using different elements at the
energy bond points than is used for normal temp organisms allows for
much higher temperature tolerance, as the bonds are much tighter, and
require higher energy input to break them apart, however this makes for
a very tightly bound molecule that only does its chemical work at a
higher temperature. For example, a common protein in bacteria which uses
iron in its makeup, has a corollary protein in hyperthermophilic
bacteria (bacteria that can live above boiling) that uses tungsten
instead.
These bacteria have been recovered from deep sea volcanic vents, deep
oil wells, and deep geothermal systems, and have exhibitied preference
for temperatures above 180 degrees F (about 90 C) up to as much as 275 F
(about 130 C). As more varieties are recovered, the upper limit seems to
creep higher, especially as specemins are recovered from deeper and
deeper sites.
Mike