It wasn't until 80 years after the famous ship, the Titanic, sank to its icy grave that we were able to venture to the depths of the Atlantic Ocean and examine its remains. It wasn't that we didn't know where to look for the infamous ship. After all, there were records of where survivors were rescued and estimates of the location of the final call for help. No, our inability to explore the ruins was due primarily to the extreme depths to which the ship had sunk. Until recently, we did not have the technology to withstand the enormous pressures experienced when diving to the very bottom of the world's deepest bodies of water. As one delves deeper into a body of water, the pressure experienced increases. The opposite happens when one climbs a tall mountain, at higher altitudes the atmospheric~pressure is less than at lower elevations. Therefore, the air is "thinner" the higher you go. For humans, it is difficult to survive at extreme elevations or in the depths of the ocean without advanced technology. For extremophiles, pressure doesn't present as much of a challenge.
Barophiles, also known as piezophiles, are extremophiles that thrive under extremely high pressures. In fact, exploration of the deepest trench on Earth has revealed obligatory barophiles. At Mariana trench, the deepest seafloor at a depth of over 10,000 meters, life was found flourishing around deep sea vents. The microorganisms here thrive at pressures of 70 to 80 MPa (the atmospheric~pressure at sea level is only 101 kPa) but can't survive at lower pressures of only 50 MPa; earning them the distinction of obligatory barophiles. Why can an increase in pressure have such dramatic effects on some organisms and not on others? An increase in pressure causes cellular membranes to become much less fluid, a sever problem for living organisms. Extremely high pressures can also cause damage to nucleic acids and proteins, both essential molecules for living organisms. Finally, many chemical reactions in the cell result in an increase in volume. An increase of pressure generally results in a decrease in volume. Therefore, at high pressures volume will be restricted, thereby restricting life's chemical reactions from occurring efficiently.
Scientists don't yet know all the mechanisms by which barophiles cope with high pressures. However, many microorganisms have adapted to combat loss of membrane fluidity due to high pressures by incorporating a greater percentage of unsaturated fatty acids into the lipid membrane. Another adaptive mechanism may be to increase the natural rates of DNA or protein repair, undoing the damage induced by high pressures. As humans, reaching the depths of the oceans for the first time revealed a world of living creatures on our planet never thought to be able to exist. There was little doubt that the extreme temperatures and pressures at the bottom of the ocean would prevent life from taking hold. Instead, we found a diversity of life almost unimaginable. Maybe we will discover another pocket of seemingly impossible life again one day, maybe on another planet. Pushing our understanding of the limits of life on our own planet will serve to prepare us for that day.