Karen Lloyd on the Deep Underground Biosphere and Strange Life Forms

The Hidden World Beneath Our Feet

• 💡 Life exists kilometers deep within the Earth's crust, far beyond what we typically consider the subsurface.
• 🦠 These are not just a few species but vast numbers of microbes, including entirely new phyla on the tree of life, distinct from surface organisms.
• 🔬 Scientists access these deep-dwelling microbes through expensive drilling operations or by studying samples brought up by hot springs in subduction zones.

Extreme Environments and Energy Sources

• 💧 The deep subsurface can contain ancient, isolated water bodies that have remained liquid for billions of years.
• ⚡ Some microbes thrive in environments with abundant chemical reactions and tectonic activity, utilizing energy sources like hydrogen produced through serpentinization.
• ☢️ A fascinating energy source for some subsurface life is the radioactive decay of elements in the Earth's crust, which splits water molecules to produce hydrogen.
• ⚡ Other microbes directly utilize electrons by moving them through protein appendages, bypassing chemical diffusion.

Microbial Life and Evolution

• 🧬 The deep subsurface harbors a massive ecosystem with estimates of 10^29 living microbial cells, though their biomass is less than surface plants.
• 🌐 While many microbes are endemic to specific locations, some, like the "Sulfuroxidator" (meaning bold traveler), have seemingly unchanged genomes found globally.
• 🦠 These microbes are often slow-growing, with cell division rates of weeks rather than hours, and can survive on minimal resources like buried organic matter.
• 🔬 Chirality of amino acids is used to infer that these microbes are actively maintaining themselves, suggesting incredibly long lifespans, potentially millennia.

The Asgard Archaea and the Origin of Eukaryotes

• 🧬 A significant discovery is the Asgard archaeota, a group of microbes that possess DNA for eukaryotic cellular structures like organelles, blurring the lines between Archaea and Eukaryotes.
• 🦠 These organisms are hypothesized to be direct ancestors of eukaryotes, predating the acquisition of mitochondria.
• 🔬 Their existence challenges our understanding of cellular complexity and evolution, suggesting a gradual transition from simpler prokaryotic life.

Implications for Extraterrestrial Life

• 🚀 The existence of diverse subsurface life on Earth significantly impacts the search for life on other celestial bodies like Mars and Europa.
• 🌊 Europa's subsurface liquid oceans are considered prime candidates for harboring life due to exploitable energy gradients.
• 💨 Mars's subsurface is also a target, with methane emissions serving as potential biosignatures, though volcanic activity could also explain them.
• 👽 The possibility of a shadow biosphere with non-DNA-based life remains, though current detection methods primarily rely on DNA analysis.

Life's Role in Earth's Systems

• 🌍 Subsurface microbes play a crucial role in Earth's redox state, influencing mineral deposits and atmospheric oxygen levels over geological time.
• ♻️ They are being explored for carbon sequestration technologies, helping to reverse human-induced climate change by storing CO2 underground, though challenges remain in ensuring its long-term stability.
• 🔬 Future research requires increased investment in deep drilling to directly sample and study these organisms, potentially leading to new biotechnologies and a deeper understanding of life itself.