Sentence:  Metazoan life was in full swing by the early phases of the <WSD>Ediacaran</WSD>, approximately 650 million years ago, but these first steps were small aggregations of cells with little more than eyespots or early cups of pigment lined with photoreceptive cells. 
Meaning of the word marked with <WSD> tags:  The Ediacaran period. (from 20th c.)