Geology Notes Unit 2 - September 23rd, 2020

Chapter 1: An Introduction to Geology, p. 19-20 Intro - The Earth is divided based on its physical properties; usually based on the state of its layers and their toughness, examples area the lithosphere, asthenosphere, outer core, and inner core - The chemical and physical layers of the Earth help us better understand its geological processes such as volcanism, earthquakes, and mountain formation Earth’s Crust - The crust is the thin, rocky layer that surrounds the exterior of Earth; it’s composed of two different types- continental crust and oceanic crust . - Oceanic crust is approximately 7km thick and is made up of basalt , a dark igneous rock - Continental crust however is roughly 35km thick and can even be double that amount in mountain regions like the Rockies and Himalayas , in contrast to oceanic crust , it has a relatively homogeneous chemical composition - Continental crust is usually made up of a granitic rock called granodiorite Earth’s Mantle - Over 82 percent of the Earth’s volume is stored in the mantle , which is a solid, rocky shell that is about 2900km deep - The crust and the mantle boundary has a change in chemical composition - The majority of the rock found in the uppermost part of the Earth’s mantle is peridotite, rich in magnesium and iron that is found in both parts of the crust The Upper Mantle - Extends from the crust-mantle boundary about 660km deep - The upper mantle can be divided into three parts, the lithosphere , the asthenosphere , and the transition zone - The lithosphere is the stronger part of the upper mantle as it forms Earth’s cool, rigid outer shell, spanning around 100km on average going as far as 250km below the older parts of continents - The asthenosphere is the weaker part of the upper mantle in which the top part of it has a temperature and pressure system that causes slight melting - In this weak melting zone, the lithosphere mechanically detaches from the layer underneath - This allows the lithosphere to move independently from the asthenosphere - Past the asthenosphere (about 410km deep), the transition zone is reached - The uppermost part of this zone is distinct due to its sudden increase in density to approximately 3.7g/cm ³ - This density change occurs due to the minerals within the peridotite reacting to the high pressure and forms new minerals with closely packed atomic structures The Lower Mantle - Once a depth of 2900km has been reached through the Earth, the lower mantle will present itself - An increase in pressure occurs yet again and the mantle strengthens as depth increases - In spite of the rocks found in the lower mantle being strong, they have extreme temperatures and are fluid as a result