text: The Proterozoic Eon extended from 2500 Ma to 542.0 Â 1.0 Ma ( million years ago ) , and is the most recent part of the old , informally named â Precambrianâ time .
simplified: The Proterozoic Eon extended from 2500 million years ago to 542mya , and is the most recent part of the former Precambrian .