n.
1.the earliest eon in the history of the Earth from the first accretion of planetary material (around 4,600 million years ago) until the date of the oldest known rocks (about 3,800 million years ago)
Idiom of the Day
live high on/off the hog
to live very luxuriously or comfortably
My friend has been living high on the hog since he won the money in the lottery.