Dr. Ron Milo, a systems biologist and Professor at the Weizmann Institute of Science in Rehovot, Israel, quantifies the natural world. Previously the first Fellow in Systems Biology at Harvard Medical School, Milo's insights reveal that visible life is merely a delicate green layer atop the Earth, with the mass of plants significantly overshadowing that of all other organisms combined.

His findings indicate that animals represent a small fraction of Earth's biological diversity. In fact, the unseen life forms, particularly insects, outweigh humans by a factor of twenty. The tiniest organisms, including bacteria, archaea, and single-celled eukaryotes, outnumber insects nearly 80 to 1. Even viruses are abundant, with a total mass surpassing that of the human population by three to four times.

Focusing on microbes—considered the foundation of life—they have flourished on our planet since its inception and continue to dominate our ecosystems, often unnoticed. This leads us to question the boundaries of microbial life both on Earth and beyond.

Research has demonstrated that microbes can be found in every ecological niche explored thus far: from terrestrial soils to atmospheric layers, and across oceans, lakes, and rivers, they inhabit every conceivable environment, including extreme conditions like toxic runoffs and scalding hot springs.

Explorations into the ocean depths, including ancient sediment layers lying beneath, reveal microbial life surviving in nutrient-poor conditions, patiently awaiting the right stimuli to awaken.

Yet, what about the rock formations beneath these sediments? What secrets lie kilometers deep in the oceanic crust?

The Nordic lands of Norway, Sweden, and Finland extend like three crooked fingers into the Norwegian Sea. At the base of this region lies the Kola Peninsula, home to a once-active Soviet research site, now in decay.

Yuri Smirnov, a geologist and poet, dedicated his career to the Kola Superdeep Borehole project, initiated to outdo the American Project Mohole, which sought to penetrate the Earth's crust. Over 25 years, Smirnov contributed to the deepest man-made hole, reaching 7.5 miles (12,262 meters) into the Earth's crust, while his personal life remained overshadowed by his obsession with this project.

The Earth's crust, a rocky shell enveloping the planet, varies in thickness—thicker on land and thinner beneath oceans. Despite extensive drilling, the Kola project has barely scratched the surface of the Baltic Shield, remaining far from the mantle, which plays a pivotal role in Earth's geology.

Through these depths, they discovered ancient microscopic plankton fossils over 2 billion years old and found water trapped in fractures, likely originating from deep crustal minerals. Remarkably, they uncovered large hydrogen deposits, causing the drilling mud to bubble with escaping gas.

The mysterious fate of the Soviet submarine K-129 serves as another chapter in this exploration narrative. After sinking in 1968, a U.S. salvage mission led to the recovery of part of the vessel, but much was lost in the process, including vital nuclear materials.

The Hughes Glomar Explorer, a ship constructed for this operation, later transitioned to deep-sea mining and scientific research, including significant contributions to oceanic drilling projects. The vessel was designed to reach unprecedented depths, marking a race in technological advances in drilling capabilities.

The Glomar Challenger, another pioneering vessel, was capable of reaching depths of 7 kilometers, gathering samples that reshaped our understanding of microbial life in oceanic settings.

Research into hydrothermal vents in the 1970s unveiled ecosystems thriving in extreme conditions, reliant on the energy produced by these vents, rather than sunlight. This discovery highlighted the importance of bacterial populations in such environments.

Subsequent studies demonstrated microbes could thrive at extreme temperatures and pressures, deepening our understanding of life's resilience.

In the ongoing quest to discover microbial life beneath the ocean floor, researchers like Ingunn Hindenes Thorseth have made significant strides, revealing evidence of microbial activity in volcanic rock beneath the sea, despite the challenges posed by the environment.

The search for life in these extreme conditions not only informs our understanding of Earth's biology but also shapes how we explore for life elsewhere in the solar system and beyond.

Thank you for accompanying me on this journey through the depths of our planet, where the intersection of biology, geology, and technology reveals the astonishing resilience of life.

If you appreciate these explorations into science and history, consider checking out more stories:

• LUCA — The Last Universal Common Ancestor

  “…whilst this planet has gone circling on according to the fixed law of gravity, from so simple a beginning endless…”

• Ocelloids — The Eyes of the Carnivorous Algae!!

  Photosynthetic and predatory algae with camera-like eyes are an evolutionary conundrum.