The Hadean Era was the first in Earth history, extending from the first formation of continental crust, which began some time around 4,200 Ma (Goodwin 1991, Condie 1997), becoming persistent soon after, to approximately 3,500 Ma.
This is something you should have learned in Jr. High Science class.
Nice touch, attacking my intelligence. But I can google too. :)
http://www.peripatus.gen.nz/Paleontology/Hadean.html
“The Hadean Era was the first in Earth history, extending from the first formation of continental crust, which began some time around 4,200 Ma (Goodwin 1991, Condie 1997), becoming persistent soon after, to approximately 3,500 Ma.”