Mes·o·prot·er·o·zo·ic 
(mĕz′ō-prŏt′ər-ə-zōĭk, -prō′tər-, mĕs′-)
(mĕz′ō-prŏt′ər-ə-zōĭk, -prō′tər-, mĕs′-)adj.
Of, relating to, or being the middle of the three eras of the Proterozoic Eon, from approximately 1.6 billion to 1.0 billion years ago, marked by the formation of the first known supercontinent and the evolution of sexual reproduction. See Table at geologic time.
n.
The Mesoproterozoic Era.