3-2What Keeps Us and Other Organisms Alive?

3-2-3 Three Factors Sustain Life on Earth

◎ The one-way flow of high-quality energy from the sun.

◎ The cycling of matter or nutrients.

◎ Gravity.

維持地球上生命生存的三元素：
(1) 太陽能
(2) 物質循環或營養物
(3) 地心引力