Physical Geology Lecture 2: The Earth's Spheres PDF

# Physical Geology ## Lecture 2: The Earth's Spheres **Prof. Dr. Raafat Zaki** **Dr. Ahmed Gomaa** **Physical Geology (G101)** ### The Solar System The Solar System that we live in consists of a medium-sized star (the Sun) with eight planets orbiting it. The planets are of two different types....

# Physical Geology ## Lecture 2: The Earth's Spheres **Prof. Dr. Raafat Zaki** **Dr. Ahmed Gomaa** **Physical Geology (G101)** ### The Solar System The Solar System that we live in consists of a medium-sized star (the Sun) with eight planets orbiting it. The planets are of two different types. ### The Inner Planets (Terrestrial Planets) - Rocky planets near the Sun - Mercury, Venus, Earth & Mars - Small, high density, rocky, poor in ice and H/He and no rings ### The Outer Planets (Jovian Planets) - Giant gaseous plantes - Jupiter, Saturn, Uranus, Neptune - Large, low density, gaseous (H, He, *CH₄*), rotate rapidly. - All have rings and many moons. - Pluto, a small icy minor planet (?) ### Differences between Inner and Outer Planets: | Feature | Inner Planets | Outer Planets | |---|---|---| | Density | 3 g/cm³ or more | 1.6 g/cm³ or less | ## Origin of the Earth and the Solar System: **The Nebular Theory** - Nebular Hypothesis - **Self-gravity contracts a gas cloud.** - **Conservation of angular momentum pulls cloud into a disk.** - **Disk begins to rotate.** - **Central mass forms (proto-Sun).** - **Centrifugal force balances gravitational forces and a ring forms.** - **Ring forms into a planet.** ### How did our solar system come to be? - It all began about 4.6 billion years ago in a wispy cloud of gas and dust. - At some point, part of the cloud collapsed in on itself, possibly because the shockwave of a nearby supernova explosion caused it to compress. - The result: a flat spinning disk of dust and gas. - When enough material collected at this disk's center, nuclear fusion began. Our sun was born. It gobbled up 99.8% of all the material. - These clumps became planets, dwarf planets, asteroids, comets, and moons. - Only rocky things could survive close to the sun, so gaseous and icy material collected further away. That's how our solar system came to be the place it is today! - Comets and asteroids are the left over remains of the solar system's formation. ## How Old is the Earth? - Age of the Earth - 4.5 to 4.6 billion years (4,500,000,000 to 4,600,000,000 years) as determined through radiometric dating (Uranium, Thorium) using an instrument called a mass spectrometer. ### Where do we find the oldest rocks on Earth? - **Canadian Shield**. (NW Territories near Great Slave Lake, 3.96 by). - Before this, oldest rocks known were from Isukasia region of Greenland (3.8 by). ## The Earth's Layers ### The Hydrosphere - It includes water in streams, lakes, and oceans; in the atmosphere; and frozen in glaciers. - Oceans cover around 72% of our planet. - About 1% of the earth's total water and 22% of the earth's freshwater occurs as groundwater. ### The Atmosphere - The atmosphere is a mixture of gases, mostly nitrogen and oxygen. - 99 % is concentrated within 30 kilometers of the Earth's surface. - Few traces remain even 10,000 kilometers above the surface. - There are several layers to the atmosphere: - **Exosphere** - 1200°C - **Thermosphere** - -86.5 to 1200°C - **Mesosphere** - 2.5 to -86.5°C - **Stratosphere** - -56.5 to 2.5°C - **Troposphere** - 15 to -56.5°C ### The Biosphere - Is the thin zone near the Earth’s surface that is inhabited by life. - Includes the uppermost solid Earth, the hydrosphere, and the lower parts of the atmosphere. ### The Crust - The crust is the earth's outermost thinnest layer. - **Oceanic crust** - 5 to 10 kilometers thick. - **Continental crust** - about 20 to 40 kilometers thick. - **The Moho Discontinuity** is a discontinuous layer separating crust and mantle. #### The Oceanic Crust (SiMa) - Is thinner, denser, and contains less silica and aluminium and more magnesium and iron than the continental crust. - The lack of silica makes it darker than the continental crust. - Oceanic ridges generate new crust at the rate of 17 km³ per year. - At continental boundaries, a similar amount of material is subducted and recycled. #### The Continental Crust (SiAl) - The continental crust is thicker and made of less dense material than the oceanic crust. ### The Mantle - It is almost 2900 km thick. - It makes up 80% of the Earth’s volume - Temperature increases with depth with an average gradient of 25° C per km. - The asthenosphere is a plastic, partially molten and 350 km thick layer - Gutenberg Discontinuity is a transition zone between the lower mantle and the outer core boundary. ### The Core - Is the innermost of the Earth’s layers. - Its radius is about 3470 km. - It is composed largely of iron and nickel. - 2,260 km thick liquid (molten) outer core. - 1,228 km thick solid inner core. ## Methods to Infer Interior of the Earth ### Mantle Xenoliths - Xenoliths are pieces of mantle within the lava that provide information about the upper mantle. ### Volcanism - Volcanism provides another piece of evidence of information about the upper mantle. ### Drilling - Drilling is a tool to understand the earth's interior. - It is limited to a few kilometers due to the increased geothermal gradient within the earth's crust. - Kola Superdeep Borehole drilled from 1989 to 1994 is about 12 km deep in the northern Kola Peninsula, NW Soviet Union, Russia. ### Meteorites - They provide excellent information about the earth's interior and are thought to be remnants of the core and mantle of planets from the Solar System. ### Seismic Waves - Seismic waves provide the most comprehensive picture of the earth's interior. ## Thanks a lot **Dr. Ahmed Gomaa** **Physical Geology (G101)**