why life flourish on earth
the position to sun
early life-forms altered the environment
<b>earliest atmosphere</b>
from volcanoes
methane and carbon dioxide
early 》present
warm the earth when the sun not brigjhly
photosynthetic life-forms transformed the chemical composition of Earth’s atmosphere
remove carbon dioxide
release O2
oxygen release improved conditions for life
<div><b>is essential for</b></div><div><b>the metabolic process</b></div>
form a protective shield
today ozone shield absorbs UV
early :water absorbed the UV radiation
other planet ： no
