Beneath the Earth's surface lies a hidden realm of microscopic life, a world of 'intraterrestrials' that have been 'sleeping' for millions of years. These organisms, buried deep within the oceanic seafloor sediments, have evolved to survive in some of the planet's harshest conditions. Scientists are now on a quest to uncover these microbes, but how do they evolve to stop growing for thousands of years? The answer lies in understanding the unique evolutionary cues that drive their survival.
Imagine a world where life spans only a day. These 'day-lifespan' organisms would be perplexed by the concept of long-term survival. Similarly, the intraterrestrials, with lifespans spanning millions of years, may be waiting for geological events that occur on timescales far beyond human comprehension. The key to their survival lies in adapting to these slow, geological rhythms.
The intraterrestrials' evolutionary strategy is to enter a dormant state, a state of 'nongrowth' that allows them to endure the harsh conditions of the deep subsurface. This raises questions about the mechanisms of evolution in organisms that seemingly never produce offspring. How can they adapt to such a long-term nongrowth state?
The answer may lie in the concept of 'dormancy' and 'growth advantage in stationary phase' (GASP). Just as organisms enter a dormant state during winter to survive harsh conditions, intraterrestrials may be waiting for geological events that occur on timescales of thousands to millions of years. These events could include volcanic eruptions, island subsidence, or the slow movement of tectonic plates.
The evolutionary payoff for these microbes is to return to the upper seafloor, where they can resume growth and pass their genes to future generations. This process, known as 'natural selection', ensures that the individuals with the best adaptations to dormancy become stable in the communities. So, the intraterrestrials' 'summer' may be the moment they return to the surface, where the food is more nutritious, and they can thrive once again.
