Chapter 1: Introduction
Key terms * Asthenosphere – A subdivision of the mantle situated below the lithosphere. This zone of weak material exists below a depth of about 100 km and in some regions extends as deep as 700 km. The rock within this zone is easily deformed. * Hypothesis – A tentative explanation that is then tested to determine if it is valid. * Mantle – One of Earth’s compositional layers. The solid rocky shell that extends from the base of the crust to a depth of 2900 km. * Open system – A system in which both matter and energy flow into and out of the system. Most natural systems are of this type. * Closed system – A system that is self-contained with regard to matter- that is, no matter enters of leaves. * Igneous rock – Rock formed from the crystallization of magma. * Metamorphic rock – Rock formed by the alteration of preexisting rock deep within Earth (but still in the solid state) by heat, pressure, and/or chemically active fluids. * Outer core – A layer beneath the mantle about 2270 km (1410 miles) thick, which has the properties of a liquid. * Sedimentary rock – Rock formed from the weathered products of preexisting rocks that have been transported, deposited, and lithified * Core – The innermost layer of Earth based on composition. It is thought to be largely an iron-nickel alloy with minor amounts of oxygen, silicon, and sulfur. * Inner Core – The solid innermost layer of Earth, about 1216 km (754 miles) in radius. * Mid-ocean ridge – A continuous mountainous ridge on the floor of all the major ocean basins and varying in width from 500 to 5000 km (300 to 3000 miles). The rifts at the crests of the these ridges represent divergent plate boundaries. * Planets – A celestial body moving in an elliptical orbit around a star. * Solar nebula – The cloud of interstellar gas and/or dust from which the bodies of our solar system formed. * Crust – The very thin outermost layer of Earth. * Lithosphere – The rigid outer layer of Earth, including the crust and upper mantle. * Nebular hypothesis – The theory that the solar and stellar systems were developed from a primeval (ancient) nebula. * Relative dating – Rocks and structures are placed in their proper sequence or order. Only the chronological order of events is determined. * System – A group of interacting or interdependent parts that form a complex whole.
Concepts to know: 1. A hypothesis differs from a theory in that it is an unproven idea, developed as a strategy to obtain a sound scientific a theory. A theory is well-tested, and widely excepted, explained by certain observable facts. 2. A system as defined above can be open or closed. A closed system is self-contained in regards to matter, whereas an open system can be affected by outside factors in regards to matter. 3. The three major rock types are igneous, sedimentary, and metamorphic. Igneous rocks can be intrusive (formed underneath the earth’s crust, cooling magma) or extrusive (outside the Earth, cooling lava), and are formed by the crystallization of magma. Sedimentary rocks can be detrital (originate from the transport of solid particles) or chemical (when material dissolved in water precipitates), and are formed by weathering of other rocks, producing sediments, that form into large solid particles because of pressure or other external factors. Metamorphic rocks are formed by the alteration of preexisting rock deep within Earth (but still in the solid state) by heat, pressure, and/or chemically active fluids. 4. The rock cycle begins when magma cools forming igneous rock. That rock depending on whether it is intrusive or extrusive can make it to the Earth’s surface. If extrusive, with the assistance of weathering and other factors, causes broken down rock to be deposited as sediment. There, sediments transform through a lithification process, where it is compacted and