What is the Earths Crust?
Earth’s crust Uppermost part of the earth. It varies from 30 to 70 kilometres beneath the continents, to only 6 to 8 kilometres beneath the oceans. In geology, a crust is the outer layer of a planet, part of its lithosphere. Planetary crusts are generally composed of a less dense material than that of its deeper layers. The crust of the Earth is composed mainly of basalt and granite. It is cooler and more rigid than the deeper layers of the mantle and core. http://en.wikipedia.org/wiki/Earth& http://www.ackadia.com/…/…rals-glossary.
The Earth’s crust is its top layer, with a thickness of 5 km (3 mi) to 10 km (6 mi) for the oceanic crust, and 30 km (20 mi) to 50 km (30 mi) for the continental crust. This is less than 1% of the entire depth of the Earth. The crust is differentiated into an oceanic portion, composed of denser rocks such as basalt, diabase, and gabbro, and a continental crust portion, composed of lighter rocks such as granite. The Earth’s crust initially formed in the Hadean Eon, between 4.6 and 3.9 billion years ago. The Earth began as a molten ball of rock, but within 100-150 million years, the surface cooled and hardened. The heavier elements, such as iron and nickel, mostly sank to the Earth’s core, leaving the lighter elements at the top. Today, the oldest known rocks are zircons from the Canadian Shield dated to 4.4 billion years ago. The present-day crust itself has a range of ages, from greater than 3 billion years old to less than a hundred million years old for oceanic crust. Both the contin
