Planet Microbe – Essential Exam Notes

Big Questions & Focus

• Central inquiry: How does life arise, diversify, co-evolve with environments, and what will its future look like?
• Today’s lens: “Planet Microbe” — examining microbial life, especially in the oceans and deep sea.

What Is a Microbe?

• Two prokaryotic domains: Bacteria & Archaea (single-celled, no true nucleus, single circular chromosome, no membrane-bound organelles, divide by binary fission).
• Eukaryotes (humans, owl mascot, etc.) form only one small branch of life; all other branches on the universal tree are microbial.

Origin, Diversity & Abundance

• First microbes emerged ≈ 3.5 \text{ billion} years ago → vast time to colonize every ecological & metabolic niche.
• Abundance stats:
  • 10^8 (≈ 100{,}000{,}000) cells in just one gram of soil.
  • Total microbial carbon biomass > combined plants + animals.
  • Total microbial cells on Earth exceed the number of stars in the observable universe.
• DNA-sequencing advances reveal an ever-expanding microbial tree with immense undiscovered diversity.

Forms & Functions

• Morphology ranges from invisible single cells to larger, colored, structured mats.
• Key planetary roles:
  • Food production (e.g., fermentation).
  • Nitrogen fixation for crops.
  • Human microbiome (skin, gut).
  • Source of many medicines.
  • Foundation of forests, coral reefs, other ecosystems.
  • "First responders" in environmental crises (e.g., Deepwater Horizon oil biodegradation).

Oceans & Seafloor Relevance

• Oceans provide prime environments for studying microbes, especially extreme/novel metabolisms.
• Bathymetry (water removed) reveals tectonic features and underwater volcanoes—hotspots for unique microbial life.
• Mid-Ocean Ridge: world’s longest mountain chain, 50{,}000\,\text{km} underwater, critical zone for deep-sea microbial ecosystems.