Compared to Earth over most of its 4 to 6-billion-year history, the world we live in today is quite (i)____________. Of course, it is human nature to regard the world that we are used to as (ii)____________. The oceans, prairies, and mountain chains – even the air we breathe – seem the norm and therefore (iii)____________. A. bountiful B. invaluable C. eternal D. atypical E. permanent F. precious G. stable H. corrupted I. endangered