In addition to facing dangerous creatures and harsh environmental conditions, space explorers must occasionally contend with xenobiological hazards-nonsentient forms of life that are, by their verynature, menacing and dangerous without being openly adversarial.
Xenobiological hazards are treated more like traps than creatures. They have Challenge Ratings (CRs), and heroes earn experience points for surviving or overcoming them. A xenobiological hazard might be a pool of corrosive slime or a patch of mold that feeds on the warmth of nearby life forms. It's not deliberately predatory, just dangerous by nature.
Two kinds of xenobiological hazards are described here.