Earth - History Flashcards
When did Earth form?
4.5 BYA
Protoplanetary Disk
This is an accretion disk feeding a central star
How did Earth emerge?
Dust and gas in protoplanetary creating planetismals by electrostatic and gravitiation influence, which gradually collied and accrete
How did the moon form?
Earth collision with Theia, a mars-sized planet.
What does Earth composition depend on?
Density differences and gravitational influences
What was the early earth composed of?
The core like heavy elements like iron and nickel, whilst the crust/mantle composed of silicates, water and air, which are buoyant.
How much of the Earths volume and mass is the core?
16% and 32% respectively.
Bullen Discontinuity
This separates the liquidic outer core from the solid inner core
What is the inner and outer core seperated by?
The Bullen discontinuity.
How does Earth density change with depth?
Crust is 3cm^3, 5cm^3 and the core about 12cm^3
How much of the Earths volume and mass is the mantle?
85% and 67%
Function of the mantle
Convection currents drive tectonic activity, and forms the crust
Peridotites
Ultrabasic or ultramafic intrusive rocks, being dense and coarse-grained texture, as layered igneous complex
Fracture Zones
Valleys that cut across midocean ridges, providing passage for flow of cold bottom water between basins
Xenoliths
Fragments of mantle brought to Earths surface during eruptions
How does the crust form?
Partial melts from the mantle
Seismic Waves
These are waves eminating from a source like explosision and shock waves, until reflected from a surface.
P Waves
Waves where particle motion is parallel to wave motion
S(Shear) Waves
Waves where particle motion is perpendicular to wave motion.
Where does the lower mantle stretch from?
The seismic discontinuity to the core-mantle boundary (660km to 2900km)
What is the lower mantle composed of?
SiO2, MgO, FeO and CaO
Process of mantle convection?
Emerge from coolness from surface relative to interior, with thermal convection, cold material sinking being dense whilst hot is light and rises.
Wilson Cycle
Models opening/closing of ocean basins, with tectonic subduction and divergence as supercontinents assemble and dissassemble.
Process of Wilson cycle…
A stable craton with a hotspot rising beneat it, heating it and causing upward swelling, where it may split
Creates an ocean basin between them which can widen thousands of miles.
Subduction zone form in ocean basin
Collision of contients inevtiable
Continental Crust
This is a granite, sedimentary and metamorphic rock layer forming contients and shallow seabeds
Oceanic Crust
Resides under oceans formed at oceanic ridges at divergent plate boundaries.
Composition of oceanic crust?
Basalt, troctolite and habbro(25% igneous and 75% sedimentary)
Composition of continental crust?
Gabbro and granitoids(95% igneous and 5% sedimentary)
When does isostasy emerge?
Density differneces in continental crust and mantle
What is the crust mineral and ion concentration?
88.1% iron, and 11.9% in oxygen, silicon and aluminium.
Why are silicate ions important?
Weathering of them forms soils and sands
What is quartz composed of?
Silicon dioxide with a tetrahedral framing, minerlisatg which forms sands
Dominant rock fo the upper mantle
Peridotite made up of olivine and pyroxene
What catalyses magma generation?
H2O addition, increasing temperatures or decreasing pressure
Bowen Reaction Series
Decsribes the crystalisation and cooling, forming distinct minerals based on type of mother insults
What are the phases of bowen series?
Ultramafic
Mafic
Intermediate
Felsic
Ultramafic
Ingeous rocks with less thant 45% silica and high Mg, Fe , Co and Ni.
Mafic
Igneous rocks with 45-55% silica, dominant in Fe and Mg, typically black.
Intermediate
55-65% silica and 5-20% quartz
Felsic
More than 65% silica, like granite and rhyolite.
