小题1: It probably arises on Mars(3’)
小题2: Life existed on Mars.(3’)
小题3:Because the rock wrapped it inside from cold and radiation/Because a rock would shield life inside it.(3’)
小题4:It was warmer and wetter, and the rocks landing on earth were larger and more frequent.(3’)
小题5: created by the impact of comet(彗星) and small planets(3’)