How and when did the earth form?

Earth formed around 4.54 billion years ago, approximately one-third the age of the universe, by accretion from the solar nebula. Volcanic outgassing probably created the primordial atmosphere and then the ocean, but the early atmosphere contained almost no oxygen.

Earth formed about 4.6 billion years ago out of a gigantic star explosion that gave birth to the sun and the rest of our solar system.