Definitions

1. adjective

relating to or denoting the earliest part of the Earth’s history, from about 3.5 to 2.5 billion years ago, when simple life forms first appeared

“The microzoic era saw the emergence of single-celled organisms in the Earth’s oceans.”

2. noun

the earliest part of the Earth’s history, from about 3.5 to 2.5 billion years ago, when simple life forms first appeared

“The microzoic period is a time of great interest for paleontologists and geologists.”