Sean Carroll's Mindscape: Science, Society, Philosophy, Culture, Arts, and Ideas 314 | Karen Lloyd on the Deep Underground Biosphere
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May 12, 2025 
Join Karen Lloyd, a microbial biogeochemist at USC and author of 'Intraterrestrials', as she unveils the secrets of Earth’s underground biosphere. Discover how resilient microbes survive in extreme conditions by tapping into electrons and ancient water sources. Explore the implications for life’s origins and the potential for extraterrestrial organisms. Lloyd also discusses groundbreaking advances in understanding the adaptations of these extremophiles and their interconnectedness with Earth’s ecosystems, challenging our traditional perspectives on life.
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Billions of Deep Microbes Exist
- Billions of distinct microbial species live deep beneath Earth's surface, spanning whole new evolutionary phyla.
- These microbes thrive kilometers underground without sunlight, oxygen, or fast metabolism.
Earth's Crust Depth Limits Drilling
- Earth's crust extends from 20 to 200 kilometers deep, but humans have only drilled about 10 kilometers.
- Life has been found many kilometers down, but the full extent remains unknown.
Bold Microbe Travellers Spread Globally
- Some microbes deep underground are globally widespread with little genomic change, e.g., Sulfurutis Otoxviator, meaning 'bold traveler.'
- Others show local specialization, showing complex subsurface microbial distributions.