Billion-year time span (3)
I believe the answer is:
eon
(Other definitions for eon that I've seen before include "Era" , "Geological period" , "Vast age (alt. sp.)" , "thousand million years" , "In time, long division" .)
I believe the answer is:
eon
(Other definitions for eon that I've seen before include "Era" , "Geological period" , "Vast age (alt. sp.)" , "thousand million years" , "In time, long division" .)