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Introduction To Physical Geology The Science • Geology is typically broken up into two fields of study – Physical Geology – Historical Geology Physical Geology • Examines the materials composing Earth and seeks to understand the processes that operate beneath the surface – It is the how and why of Geology Historical Geology • Seeks an understanding of the origin of Earth and its development through time. – It is the who, what, where, and when The rock cycle The rock cycle - Series of processes by which rocks changes into other types of rocks - Illustrates various processes and paths as earth materials change both on the surface and inside the Earth - What are the three main rocks ? 1- Igneous 2- Metamorphic 3- Sedimentary The rock cycle Fundamental Rock Types - Igneous Rocks: solidify from melt, e.g. lava (extrusive) or magma (intrusive) - Sedimentary Rocks: are made at the Earth’s surface from particle and chemical remnants of other rocks - Metamorphic rocks: form when other rocks are heated, squeezed, and deformed. Granite (igneous, intrusive) Basalt (igneous, extrusive) Conglomerate (sedimentary) Shale and sandstone (sedimentary) Limestone (sedimentary) Sandstone (sedimentary) Marble (metamorphic) Quartzite (metamorphic) Gneiss (metamorphic) Earth as a System – Earth’s Four Spheres • Atmosphere – • The air we breathe Hydrosphere – • The water we drink Biosphere – • life Solid Earth – Where we live All of these spheres interact with each other. A minor adjusting In the properties of one could lead to drastic changes in the Properties of the other three Earth’s Outermost Layers • The most dynamic portion of the Earth – Atmosphere • Thin gaseous envelope surrounding Earth – Hydrosphere • Water layer dominated by the oceans – Biosphere • All living things on the planet – Lithosphere • Rocky outer shell The Atmosphere Composition is unique in solar • system 78% nitrogen – 21% oxygen (not present in early – atmosphere) Minor amounts of carbon dioxide, – argon and water vapor The Hydrosphere • Total mass of water on or near the Earth’s surface – Covers 71% of Earth’s surface – ~98% in oceans – 2% in glaciers, groundwater, lakes and streams (fresh water) The Biosphere • All life on Earth – Animals & plants on land, in the sea and air – Microorganisms-the most common form of life – Evolved within narrow zone near the Earth’s surface Earth’s Internal Structure • Solid Earth has a layered structure – Layers defined by composition and physical properties – Compositional layers • crust - mantle - core – Physical layers • lithosphere - asthenosphere mesosphere - outer core - inner core Compositional Layers • Crust – Outermost compositional layer – Definite change in composition at the base of the crust – 2 types: • Continental crust • Oceanic crust Compositional Layers • Mantle – Largest layer in the Earth • 2900 km thick • 82% by volume • 68% by mass – Composed of silicate rocks with abundant iron and magnesium • Density ranges from 3.2 to 5 g/cm3 Compositional Layers • Core – Central mass about 7000km in diameter – Average density of 10.8 g/cm3 – 16% by volume, 32% of mass – Indirect evidence of composition • Metallic iron Physical Layers • Lithosphere – Crust + upper portion of the mantle – Solid & rigid – Thickness ranges from 10 km beneath oceans to 300 km in continental areas • Crust – Continental crust • Thick - up to 75 km • Lower density - 2.7 g/cm3 • Strongly deformed • Much older - may be billions of years old • Crust – Oceanic crust • Thinner - about 8 km • More dense - 3.0 g/cm3 • Comparatively undeformed • Much younger - < 200 million years old Physical Geology • Earth’s Systems – Atmosphere • gases that surround the Earth – Hydrosphere • water on or near Earth’s surface – Biosphere • all living or once-living materials – Geosphere • solid, rocky Earth Earth’s Interior • Compositional Layers – Crust • Very thin outer rocky shell of Earth • Variable thickness – Mantle • Hot solid • Special “plastic” zone • Fe-, Mg-, Si-rich minerals – Core • Outer core – liquid – mostly iron • Inner core – solid – mostly iron Earth’s internal layers The Earth in Space Age of the Earth = 4.5 Billion years [4,600,000,000 years] Age of the Universe = 14 Billion years Earth Compared to Other Planets • The Solar System – The inner planets • Rocky planets near the Sun • Mercury, Venus, Earth & Mars – The outer planets • Giant gaseous planets • Jupiter, Saturn, Uranus, Neptune – Pluto, a small icy minor planet Origin of the Solar System • Gravitational collapse of gas & dust cloud [nebula] – Rotation around a central mass – Disk shaped cloud – Temperature variations segregated matter – Small particles accreted into larger planetesimals, planets How do we Know this? • Differences between inner and outer planets: – Density – The rocky inner planets=densities of 3 g/cm3 more – The gaseous outer Planets=densities of 1.6 g/cm3 or less