Microbes living their lives on the extreme edge
AS you read this, NASA’s latest space mission is winging its way to Mars where the rover Perseverance will search for evidence of life.
When life on Earth is mentioned, we tend to think of our own species and other large life forms that are around today, but for most of our planet’s long evolutionary history the life forms that dominated were various microscopic, or near microscopic, ones that, though very different from each other, are generally lumped together under the umbrella term ‘microbes’.
Microbes are amazingly successful in that they have evolved to occupy virtually all available environmental niches. They are found living in sea ice and permafrost in polar regions, in acid lakes in volcanoes, in boiling water in hot springs, in bone-dry sand in the most arid deserts, in sediments in the deepest ocean trenches and in highly concentrated salt lakes.
Some microbes push things to the limit by surviving in such extremely toxic and hazardous man-made conditions as the waste from both chemical mines and nuclear power stations.
Maybe it shouldn’t be a surprise that microbes can tolerate such extreme conditions as they have been found in space. In the quest to understand the origin of life on Earth and advance our understanding of the potential for life elsewhere, it appears likely that microbes in space could well be seeding planetary and other celestial bodies and thriving wherever they happen to fall on fertile ground.
The presence of liquid water on Earth and oxygen in the atmosphere are believed to be the key drivers that shaped the emergence and evolution of advanced life on our planet together with the fact that our particular distance from the Sun provides a constant source of energy to power the chemical reactions that maintain life.
Whether or not other planetary bodies that we know of could, or did, support life is unclear. Further study of the extreme limits that microbes can tolerate on Earth will inform the exploration of space and narrow down possible places where extra-terrestrial life may exist.
At present the leading contenders that are the focus of attention in the quest for extra-terrestrial life are threefold: Mars, Enceladus (one of the moons of Saturn), and Europa (one of the moons of Jupiter).