Zack, Booth and others in “Aliens in a Spaceship”

(coming to realization) 6, 7, 16. Carbon, nitrogen, and sulfur on the periodic table of elements. They are buried in coal-rich soil.

You gotta narrow it down, Zack.

Keep going, Zack.

The mineral components in coal are all the same. It's the organic components that provide a unique fingerprint. They're called macerals. They fluoresce at different levels. A reflectance of 1.4 is quite rare, suggesting a high concentration of inertinite.

Zack, tell me what that means.

It means he knows where they are.