Structure and Composition of the Earth and Plate Tectonic Theory Flashcards
What is the layer between the crust and the mantle?
The Moho
What is the density of oceanic crust?
2.9 g/cm3
How thick is oceanic crust?
5-10km
What is the composition of oceanic crust?
Basalt
What is oceanic crust rich in?
Fe and Mg
What is the density of continental crust?
2.7 g/cm3
How thick is continental crust?
90km
What is the composition of continental crust?
Granite
What is continental crust rich in?
Al and Si
What is the density of the mantle?
3.3 g/cm3
What is the composition of the mantle?
Peridotite
What is the density of the core?
12 g/cm3
What is the composition of the core?
Iron and nickel
Where is the 1,300 degree isotherm?
Between the lithosphere and asthenosphere
What state is the lithosphere?
Rigid
What state is the asthenosphere?
Rheid
Where is the Gutenberg Discontinuity?
Between the mantle and the outer core
Where is the Lehmann Discontinuity?
Between the outer and inner core
What state is the outer core?
Liquid
What state is the inner core?
Solid
Define Lithospheric Plates
Regions of the Earth’s crust and upper mantle that are fractured into plates that move across a deeper plasticine mantle
What are the seven major tectonic plates?
African, Antarctic, Eurasian, Indo-Australian, North American, Pacific, South American
What are the four classifications of rock by Victor Goldschmidt?
Lithophile (rock loving), Siderophile (iron loving), Chalcophile (ore loving), Atmophile (gas loving)
What is a limitation of Goldschmidt’s Classification?
It can depend on temperature, pressure and the chemical environment e.g. pH
Define Minerals
Naturally occurring inorganic chemical compounds or elements with compositions that can be expressed as chemical formulae
What can minerals be identified through?
Compositions, Atomic structures, Physical properties
Define Silicates
Minerals that contain a fundamental building block called a silica tetrahedron
What is a silica tetrahedron made from?
Four oxygen bounding a single silicon
What are the five types of silica tetrahedron?
Single (e.g. olivine), Single chain (e.g. augite), Double chain (e.g. hornblende), Sheet (e.g. mica), Framework (e.g. quartz)
What eight diagnostic properties of minerals?
Colour, Crystal shape, Lustre, Hardness, Cleavage, Relative density, Streak, Reaction with acid
What are the four types of lustre?
Metallic, Vitreous, Greasy, Pearly
What is the hardness of a fingernail on Mohs Hardness Scale?
2.5
What is the hardness of a copper coin on Mohs Hardness Scale?
3.5
What is the hardness of a steel pin on Mohs Hardness Scale?
5.5
What are four pieces of direct evidence for the structure and composition of the earth?
Rocks at the surface, Boreholes and mines, Ophiolites, Volcanic rocks with xenoliths
What is P wave velocity affected by?
Rigidity and incompressibility
What is S wave velocity affected by?
Density and rigidity
Define Shadow Zone
Region of the earth that receives no or just some of the different seismic waves
What causes P wave shadow zones?
Due to the change from solid mantle to liquid outer core causing the P waves to slow down and refract from this surface
What causes S wave shadow zones?
Due to the change from solid to liquid outer core, the liquid doesn’t allow the S waves to propagate through it
What is the average density of the earth?
5.5 g/cm3
What are the two main types of meteorite found on earth?
Iron meteorites and Stony meteorites
What do iron meteorites represent?
The core
What do stony meteorites represent?
The crust and the mantle
What three things does the earth’s magnetic field change in?
Strength, Position of the poles relative to the axis, N and S poles intermittently switch positions
Define Geotherm
A line that shows temperature variation of rock with depth
Define Geothermal Gradient
Change in temperature over a given depth
When the geotherm is higher than the solidus…
The rock partially melts
What are four pieces of evidence which confirms the earth is hotter inside than at the surface?
Temperature in mines, Hot springs, Volcanic activity, Surface heat flow
What are two sources of internal energy/heat?
Initial heat from the Big Bang, Break down of radiogenic elements
What are six pieces of evidence to define plate boundaries?
Earthquake zones, Volcanoes, Trenches and rifts, Mountain belts, Heat flow, Variation in gravity readings and anomalies
What are three mechanisms for plate movement?
Convection currents, Ridge push, Slab pull
When are negative magnetic anomalies induced?
When the rock cools and solidifies with the Earth’s north magnetic pole in the southern geographic hemisphere
What are four factors affecting gravity?
Radius of the earth, Latitude, Altitude, Density of the rocks
