Structure of the Earth obducted onto the continental crust and preserved as ophiolite sequences. Many rocks now making up Earth's crust formed less than 100 million (1) years ago; however, the oldest known mineral grains are about 4.4 billion (4.4) years old, indicating that Earth has had a solid crust for at least 4.4 billion years. Earth's mantle extends to a depth of 2,890 km, making it the thickest layer of Earth. The mantle is divided into upper and lower mantle. The upper and lower mantle are separated by the transition zone. The lowest part of the mantle next to the core-mantle boundary is
Chaotian (geology) the Mundrabilla iron meteorite of Western Australia using the argon method determined an age of 4,570 ± 60 million years ago. The proposed collision with Theia, leading to the formation of the Moon, is estimated to have occurred 4.527 billion years ago. Outgassing and differentiation of the earth in an iron-rich core and mantle may have been completed 4.45 billion years ago. Chaotian (geology) In the geologic record the Chaotian eon or era is unofficially proposed to denote the time preceding the solidification of the Earth's crust and the formation of Earth's moon, it is the earliest era within the