From the crushing pressures at the depths of the oceans to the scorching heat of volcanoes, you would be hard pressed to find a region on earth that life has not exploited.
For decades, biologists have been finding what they believe to be the limits of life on earth, and for decades, nature has been providing species that prove them wrong. A good example of such species are the ‘extremophiles’. Coined in 1974, the term ‘extremophile’ fittingly means ‘lover of extremes’, and is used to describe organisms such as bacteria that have adapted to surviving in hostile conditions.
There are, in total, nine categories of extremophile, each focusing on survival in a different extreme or dangerous environment. Whether it be harmful levels of radiation, or extremes of pH, it is clear that microbes have mastered the art of extreme survival.
Let’s focus on the record-holder for survival at high temperatures. This thermophile (extremophile adapted to extremes of temperatures), somewhat boringly named “Strain 121”, lives by the hydrothermal vents found on the ocean floor, where on average the temperature is 100˚C. However, when taken into the lab for testing, Strain 121 was perfectly comfortable for the temperature to be cranked up, reproducing happily at temperatures reaching 121˚C, and only dying when the temperature reached at an astounding 130˚C!
Needless to say, if you were subjected to such conditions, it would not be pretty. Forget external burns: the very DNA in your cells would gain so much energy that the strands would dissociate from each other. In other words, your DNA itself would unravel! So how does Strain 121 cope with such high temperatures? Easy; its DNA is wrapped tighter. The more compactly the DNA is stored, the more energy it takes to break it up. Of course, an adaptation like this didn’t just happen overnight. I’m sure I don’t need to explain the concept of evolution; from an early age we are exposed to the ideas of Charles Darwin and his ‘Theory on the Origin of Species’. In a nutshell, survival of the fittest, is something that bacteria do extremely well, as they divide so frequently.
However, the study of extremophiles has further-reaching implications than simply survival on earth, and is, in fact, a key point of interest in the hunt for extra-terrestrial life. If, for example, the Planococcus halocryophilus OR1 bacteria can thrive at temperatures of -15˚C, what is to stop it from doing so at the sub-zero temperatures on other planets where there are similarly extreme temperatures? Like Mars, for example. So let us assume that martians have, at some point, existed (albeit in the form of microscopic bacterium). If spores of Bacillus subtilis, Chroococcidiopsis bacteria, and the lichen Xanthoria elegans can survive the conditions of a meteor crash, (namely pressures between 50,000 – 500,000 atmospheres, and brief exposure to temperatures of 1000 °C), who is to say that similar bacteria couldn’t have arrived on Earth on board an asteroid from Mars billions of years ago?
Many scientists support the idea that life on earth has its origins on Mars (a theory known as panspermia), and extremophiles are one of the most promising leads on this subject. There is still much to learn about the limits of life, but with further research into life on our planet, it might just be possible to learn more about life outside of our world.
Want to see another example of a cool extremophile?
Check out our article on “Tardigrades”, aka. “The Water Bear”.