Beneath the Earth's surface, a hidden world of microscopic life awaits discovery. These "intraterrestrials" thrive in some of the planet's harshest environments, and scientists are eager to uncover their secrets. In the book "Intraterrestrials: Discovering the Strangest Life on Earth" (Princeton University Press, 2025), Karen G. Lloyd, a microbial biogeochemist at the University of Southern California, explores the concept of evolution among organisms that can survive for hundreds of thousands, or even millions, of years in a dormant state, and what they might be waiting for to "wake up".
But here's where it gets controversial: How can an organism evolve to stop growing for thousands of years? Recent research suggests that microbes buried deep in oceanic seafloor sediments may be doing just that. These intraterrestrials, small microorganisms living inside Earth's crust, might be waiting for geological events to trigger their awakening. Imagine a human life lasting only 24 hours; it's hard to fathom, but it helps us understand the timescales these microbes operate on.
The key question arises: Can these microbes adapt to avoid cell division for thousands of years, and if so, how does evolution work for an organism that seemingly never produces offspring? Lloyd suggests that these microbes might be waiting for something as slow as island subsidence, which occurs over geological timescales. This waiting period could be the key to their survival, allowing them to take advantage of new conditions when they arise.
The concept of long-term dormancy and its evolutionary advantages is intriguing. When starved, some bacteria enter a state of long-term dormancy, where they remain metabolically active but don't grow. This growth advantage in stationary phase (GASP) may explain why intraterrestrials live so long. They might be waiting for something that only happens thousands of years later, acting like monks accustomed to deprivation while others perish.
But what are these microbes waiting for? Seasonal cycles are too fast, so geological processes like volcanic eruptions, submarine landslides, earthquakes, and tsunamis might trigger their awakening. Even glacial cycles and tectonic plate movements could play a role. The intraterrestrials might be waiting for the slow squish of plates into a continent, where they can resurface and resume growth.
The evolutionary payoff for such a long wait is significant. These microbes would pass their genes along to future generations when they return to the upper seafloor, where food is more abundant. This is the intraterrestrials' version of summer, ensuring their adaptations become stable in the communities. But is this really the point of living for hundreds of thousands of years?
The intraterrestrials' long-term survival strategy raises intriguing questions. Are we, as humans, like day-lifespan beings contemplating a tree, unable to fathom the timescales these microbes operate on? What is the point of living for such extended periods, and how does evolution work for organisms that seemingly never produce offspring? These questions invite further exploration and discussion, as we strive to understand the hidden life beneath our planet's surface.
