Summary:

- The Earth's crust is not just a lifeless layer of rock, but it actually contains a thriving ecosystem of microbes and other lifeforms.
- These microbes, called "deep biosphere," live deep underground, sometimes several kilometers below the surface, and get their energy from chemical reactions rather than sunlight.
- Studying this deep biosphere can provide insights into the origins of life on Earth and how life might exist on other planets with similar conditions.