In this activity, student teams create a knowledge map of the essential characteristics or factors of a planet with a habitable climate, identifying range of inputs, outputs and variables of a planetary environmental system. Identified characteristics are compared to extreme environments on Earth, such as the Antarctic or the Sahara desert, and are used to consider the real life challenge of searching for life in extreme environments. The resource includes a student data sheet, questions, teacher's guide and scoring rubric. This is Activity B of two activities in the first module, titled "Temperature variations and habitability," of the resource, Earth Climate Course: What Determines a Planet's Climate? The course aims to help students to develop an understanding of our environment as a system of human and natural processes that result in changes that occur over various space and time scales.