This document discusses factors that make Earth habitable and able to support life. It identifies five key factors: 1) Temperature - Life is supported within a limited temperature range on Earth's surface. 2) Water - Liquid water is essential for life processes. 3) Atmosphere - Earth's atmosphere provides insulation and protection from radiation. 4) Energy - A steady energy input, like from the sun, allows life's chemical reactions. 5) Nutrients - Earth's water cycle and volcanic activity replenish nutrients for organisms. The document examines what would happen without each factor and notes their importance in making Earth uniquely life-supporting in the solar system.