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
take it upon oneself (to do something)
to undertake to do something, to make something one's responsibility
I decided to take it upon myself to fix the broken window in our apartment.