Oceanic crust Oceanic crust Oceanic crust is the uppermost layer of the oceanic portion of a tectonic plate. It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust, composed of troctolite, gabbro and ultramafic cumulates. The crust overlies the solidified and uppermost layer of the mantle. The crust and the solid mantle layer together constitute oceanic lithosphere. Oceanic crust is primarily composed of mafic rocks, or sima, which is rich in iron and magnesium. It is thinner than continental crust, or sial, generally less than 10 kilometers thick; however it is denser,
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