For millions of years they have been waiting for their moment. What lies deep beneath the Earth?
Beneath the Earth’s surface, scientists are discovering microorganisms that can remain dormant for hundreds of thousands or even millions of years. Research suggests that they are not “dead” but are waiting for rare geological events – such as earthquakes, volcanic eruptions or tectonic plate movements – to allow them to become active again.
Beneath the Earth’s crust lies an almost unknown ecosystem of microscopic life. Microbes living deep in marine sediments and rocks function in conditions of extreme sunlight deficiency. Scientists call them intra-terrestrial organisms – creatures adapted to life in geological silence.
As Karen G. Lloyd, a biogeochemist at the University of Southern California Dornsife and author of the book “Intraterrestrials: Discovering the Strangest Life on Earth” (Princeton University Press, 2025), describes in the livescience.com website, some of these microorganisms can remain almost completely dormant for an extremely long time. They do not respond to day and night changes or to the seasons – they live too deep for it to matter to them.
Evolution in the rhythm of geology
The biogeochemist indicates that instead of the short cycles known from surface biology, intra-earth organisms can “follow” processes stretching over hundreds of thousands of years. These include the movements of tectonic plates, the formation and disappearance of ocean basins, cracks in the Earth’s crust and changes in the flow of fluids deep inside the planet.
This is a completely different scale than the one at which we usually think about evolution. Classical biology assumes that natural selection acts on populations over successive generations. Meanwhile, in the world of microorganisms living underground, the question arises: how does evolution work where cell division is extremely rare and life continues almost at a standstill?
Sleep as a survival strategy
Research indicates that the long-term dormancy of these organisms is not accidental. Microbes living deep under the ocean floor show signs of adaptation to ultra-slow metabolism. They produce enzymes specialized to work in a nutrient-poor environment and can function with minimal energy consumption.
Putting them to sleep may therefore be an evolutionary strategy. Organisms that can “wait” may gain an advantage when the environment suddenly changes and a new supply of energy or nutrients appears – initially seemingly unfavorable.
In laboratories, a similar phenomenon is observed in Escherichia coli bacteria, which, in conditions of long-term starvation, go into a state of rest, and after that they are able to compete more effectively with rapidly growing individuals. This phenomenon is known as stationary phase growth advantage.
What might “inner-earth” microbes be waiting for?
If seasonal changes are too rapid for these organisms, geological processes remain the only sensible “wake-up signal”. Volcanic eruptions, earthquakes, undersea landslides or slow movements of tectonic plates may bring them new sources of food after hundreds of thousands of years.
In the boldest hypotheses, microbes may be adapted even to glacial cycles, or until the moment when seafloor sediments are pushed back to the surface as a result of subduction (a process in which one tectonic plate – usually oceanic – slides under another – continental or other oceanic – and sinks into the Earth’s mantle) and deformation of the Earth’s crust. Such a “return to the top” could mean a chance to grow again and pass on genes to the next generations of microbes.
