Life on Earth: Extreme Environments
The search for exoplanets has revealed many environments unlike anything that can be found on Earth, or even the Solar System. By looking for life in extreme environments on Earth, scientists can better understand how life might emerge, survive and evolve in other unique environments elsewhere in the Galaxy.
The search for life in Earth's extreme environments has revealed that life can flourish in places that, at first glance, appear to be completely uninhabitable. For example, life was surprisingly found in the Mariana Trench, the deepest part of Earth's ocean, at over 1000 times the pressure experienced at sea level. In the Grand Prismatic hotspring in Yellowstone National Park, orange and brown microbial blankets are seen extending out of the nearly boiling water, shown in the image below. Deinococcus radiodurans, listed as the world's toughest bacterium by the Guinness Book of World Records, can survive acute doses of radiation of up to 500,000 rad, about 10 times the amount that the bacterium E. coli can survive, and about 1000 times the amount that a human can survive. Microbes such as Cyanidium caldarium have been found to be capable of surviving in extremely acidic environments, even at pH levels at or below 1. The list of examples is long.
The remarkable ability of life on Earth to adapt to extreme environments has led biologists and astronomers to question exactly what the requirements are for a planet to be capable of supporting life. Given life's tenacity, and the diversity of exoplanets that have been found already, many astronomers find it hard to believe that at least simple forms of life do not exist elsewhere in the Galaxy.
An important note to this discussion is that although life can adapt to and survive in extreme environments, it is not clear whether life can begin there. Life may be extraordinary at adapting, but the process of life emerging in these environments may not be possible, and it is certainly not understood. If life cannot start in extreme environments, then it is entirely possible that life will only be found on planets comparable to Earth.