Characteristic and Internal Structure of the Earth Flashcards
What shape is the Earth and why is this?
The Earth is an ‘oblate spheroid’. The bulge occurs due to the rotation of the Earth, as the Earth s slightly plastic (deformable).
What is the approximate radius of the Earth?
6378km
About how much does the Earth radius vary due to mountains and oceans?
+/- 20km
What is an equation to approximate the actual radius of the Earth considering the bulge in terms of the latitude?
R(λ) = Req(1-f*sin^2(λ))
where f is the flattening
What is the equation for f, the flattening of the Earth?
f = (Req - Rpol)/Req
What is the approximate radius from pole to pole of the Earth?
Around 22km less than at the equator.
What is latitude? What is its symbol?
Specifies the north-south position of a point on the surface. Runs from 90°N - 90°S, where 0° is the equator. Symbol can either be λ or ϕ
What is longitude? What is its symbol?
Specifies the east-west position of a point on the surface. Relative to defined meridian at Greenwich. Goes from 180°W to 180°E. Symbol can either be λ or ϕ
What is Δ in Geophysics?
Angular distance in radians.
What is the equation for actual distance in terms of angular distance?
X = Req * Δ
where Δ is the angular distance.
What is the Cavendish experiment and what was found?
Torsion balance used to measure gravitational attraction between two large masses and compare this to their weight using Newton’s law.
What is Newton’s law of universal gravitation?
F = GMm/r^2
Who drilled the deepest into the Earth and how far did they go?
Drilled to 12,262 metres before the temperature forced them to stop from 1970-1989.
What is the equation for gravitational acceleration including Req?
geq = GMe/Req
What is the integral equation for the moment of inertia?
I = integral over V of r^2 dm
What is the moment inertia of the Earth (including Me and Re?
I = 0.331MeRe^2
What are the 4 most abundant elements?
Oxygen, Magnesium, Silicon and Iron
What does mass segregation mean?
Heavier elements are more abundant near the Earths centre.
What are the layers of the Earth in order?
Crust, Mantle, Outer Core, Inner Core (mostly Fe).
What is the average thickness of the Earth’s crust (continental and oceanic)?
35km (continental) and 7km (oceanic)
What is the Mantle subdivided into? What happens at each subdivision?
Upper mantle (Olivine composition), 2 transition zones(1- high pressures cause olivine to undergo phase transition that releases heat. 2- spinek to perovskite with 10% increased density), lower mantle (core-mantle boundary).
What are the mechanical divisions of the Earth? How does this differ to the other layers?
Lithosphere, Asthenosphere, Mesosphere, Outer Core and Inner Core. This is the heat transport of materials rather than the composition and crystal structure of the Earth.
What does the Lithosphere include?
Includes crust and some of mantle - heat transport predominantly by conduction. Over geological time periods undergos brittle fracture and elastic deformation but is rigid on seismic wave timescale.
What does the Asthenosphere include?
Rigid on short timescales, and hence behaves as an elastic solid, transmitting shear and compressional elastic waves. Over geological time, sufficiently hot that viscous flow can occur, and heat transport by convection.
What does the Mesosphere include?
Becomes less ductile and more rigid with increasing pressure and temperature.
What does the outer core include?
Low-viscosity liquid, so shear waves are not transmitted, but compressional elastic waves are transmitted. Drives the geodynamo which produces Earth’s B-field.
What does the inner core include?
Solid region due to pressure-freezing, detected by reflection of seismic waves. May rotate slightly faster than rest of the Earth as it is not connected mechanically to the mantle.
What does seismic activity show evidence for?
Compressional and shear waves - indicate solid core and liquid outer core, and sharp transitions in density.
What is the composition of the Mantle rock?
Xenoliths - mantle rock brought to surface
Ophiolite - oceanic crust and underlying mantle brought to continent
What is the composition of meteorites?
Largely olivine (Mg, Fe, Si, …) with some metallic iron
What are 4 ways we can measure the age of rocks?
- Radiometric dating
- Palaeontology
- Stratigraphy
- Magnetic reversals
