In the last five decades, we have come to learn that life can be highly adaptable. Starting with the discovery of extremophiles in the 1960s, our entire understanding of how life may have evolved on Earth has been undergoing a reassessment. The early Earth would have presented a relatively inhospitable environment, suggesting to scientists that the earliest forms of life may have been extremophiles.
What is an extremophile? An extremophile is an organism that can thrive in an extreme condition that would be detrimental to most life on Earth. Let us take an example of the most complex of all known extremophiles, the tardigrade.
Tardigrades (also known as “water bears”) are 1 millimeter (0.039 in) long when fully grown, with 4 pairs of legs, each with 4-8 claws also known as “disks.” The animals are prevalent in moss and lichen and viewable with a low-power microscope.
What makes them an extremophile? The tardigrade can withstand temperatures as low as minus 273 degrees Celsius (near absolute zero) and as hot as 151 degrees Celsius (well above the boiling point of water, which is 100 degrees Celsius). It is also able to withstand pressures about six times that found in the deepest ocean trenches and ionizing radiation at doses hundreds of times higher than humans can survive. The big surprise is they can also live in the vacuum of space.
The average human can live without water for about three days, without food for about ten days, if the external environment is hospitable to humans. However, the tardigrade can go without both food and water for more than 10 years. They dry out to the point where they are less than 3% water, but can rehydrate, forage, and reproduce.
The discovery of extremophiles makes finding life on other planets and moons, even within our own solar system, more likely. For example, just recently researchers discovered bacterium, Planococcus halocryophilus OR1, in permafrost (permanently frozen ground) on Ellesmere Island (part of the Qikiqtaaluk Region of the Canadian territory of Nunavut). The organism thrives at 5 degrees Fahrenheit (minus 15 degrees Celsius). This discovery offers clues as to the type of life we may find on Mars or Saturn’s moon Enceladus, both of which contain water ice and surface temperatures well below freezing.
What we humans consider hospitable conditions may actually be lethal to extremophiles. For example, the microorganism Ferroplasma acidiphilum needs large amounts of iron to survive. The iron amounts they thrive in would kill most other life forms. On Earth, many extremophiles live deep underground, which was previously thought to be a dead zone for life, due to the absence of sunlight. However, now we know that the majority of our planet’s bacteria live underground.
The planet Mars has two polar ice caps, which consist primarily of water ice. What might we find as we explore these and the surrounding regions? Saturn’s moon Enceladus appears to have liquid water under its icy surface. Because of Enceladus’s apparent water near the surface, it is a prime candidate for extraterrestrial life in the form of extremophiles.
In my YouTube video, introducing my book, Unraveling the Universe’s Mysteries, I predicted that we would likely find extraterrestrial life in our own solar system within the next twenty years. I stand by that prediction. In fact, I believe I am being conservative.
I suggest we prepare ourselves. We may be on the verge of discovering life in our own solar system.
- Wikipedia http://en.wikipedia.org/wiki/Tardigrade
- How Stuff Works, “How Extremophiles Work” http://science.howstuffworks.com/life/cellular-microscopic/extremophile.htm
- Live Science, “Cold-Loving Bacteria Offer Clues for Life on Mars” http://www.livescience.com/34657-coldest-temperature-bacteria-found-in-permafrost.html
Image: Wikipedia Commons - The tardigrade Hypsibius dujardini