Total 115 Points Range 48-113 Scores 42-98% Mean = 74% High grade kudos goes to: Jason Sadowski Best written essays go to: Ruchi Patel SADOWSKI JASON
Earths Core and the Geodynamo System
Earths Core
Earths Core
Earths Core The Geodynamo System is that system that owes its origination in Earths Outer Core. Its effect as a result of the generation of Earths magnetic eld reaches far into outer space producing a protective shield that permits the development of Earths complex atmosphere and complex biological life.
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Forming the planets from planetesimals: Planetesimals grow by continuous collisions. Gradually, Formation of Proto-Planet an irregularly shaped proto-Earth develops. The interior heats up and becomes soft
molten Fe because of its density and gravitational interactions, began to sink to the center of the early Earth
Gravity reshapes the proto-Planet collide and stick together, forming into a sphere. The interior of the planetesimals. Planet separates into a core and mantle.
Dust particles
Planetary Cores
Subdivisions of the Earth
We can also infer whats at the center of the Earth. The S-wave
So we knowEarth's iron core consists of a solid inner core about 1,500 miles (2,400 kilometers) in diameter (about the size of the moon) and a uid outer core measures about 4,200 miles (7,000 kilometers) across, about the diameter of Mars!
shadow zone is observed as shear waves cannot pass through the liquid outer core
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One question we want to ask is what is the source(s) of Earths Heat / Energy? 1) External Sources ...primarily the Sun 2) Internal Sources Radius = 6370 kilometers = 4000 miles
As the proto-Earth grew in size its increased gravitational eld would have attracted even more particles / planetary bodies. The composition of these colliding particles and planetary bodies included metal-rich fragments (i.e.., iron meteorites), rocky fragments (i.e., stony meteorites), and icy fragments (i.e., comets).
Such particles travel at great velocities, typically ~30,000--50,000 km/hr, similar to that of the Earth as it rotates around the Sun. The extreme amount of kinetic energy inherent in these moving bodies is instantly converted to heat energy upon impact, thus providing a component to the Earth's internal heat source.
Thus, Earths internal heat energy was much greater in the early stages of the Earth than it is today, having accumulated rapidly by heat conversion associated with these (1) extraterrestrial impacts, but also from. (2) gravitational contraction of the Earth's interior, and (3) the radioactive decay of unstable isotopes. All of these three processes, would have been most intense during the rst few hundred thousand years of the Earth's history
(3) the radioactive decay of unstable isotopes. Radioactive elements are inherently unstable, breaking down over time to more stable forms. (eg U-238 to Pb-206). All such radioactive decay processes release heat as a by product of the on-going reaction. In its early stages of formation, the young Earth had a greater complement of radioactive elements, but many of these (e.g., aluminum-26) are short-lived and have decayed to near extinction. More lengthy rate of decay are still undergoing this radioactive process, thus still releasing heat energy. The greater complement of unstable elements in the early Earth thus generated a greater amount of heat energy in its initial stages of formation.
Another look inside Earth.
CMB
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Another look inside Earth.
Over its 4.5 billion history, Earth's layers of molten rock evolved and crystallized, cooling from a magma ocean (yellow) to the mantle (grey) around the planet's core (orange).
Rotation of the Inner Core.The whole Earth spins completely around once a day, while the Inner Core rotates an extra one to three degrees or so each year. In approximately 360 to 120 years, the core completes an extra rotationap
Radius = 6370 kilometers = 4000 miles
Convection in the outer Core
Convection in the outer Core
Convection in uid outer core + rotation of inner Fe core at a variable rate from the liquid outer core = magnetic Magnetic dynamo eld lines
Convection in uid outer core + rotation of inner Fe core at a variable rate from the liquid outer core = magnetic dynamo
Earths Core and Earths Magnetic Field
Origin of the Magnetic Field Magnetic elds are produced by the motion of electrical charges. e.g., the magnetic eld of a bar magnet results from the motion of negatively charged electrons in the magnet. The origin of the Earth's magnetic eld is not completely understood, but is thought to be associated with electrical currents produced by the coupling of convective effects and rotation within Earths spinning liquid metallic outer core of iron and nickel. This mechanism is termed the dynamo effect.
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Earths Geodynamo System
a dipolar magnetic field...much like a bar magnet
Magnetite filings
Earths Rotational pole versus its Magnetic pole
Magnetic declination
Compass
Magnetic declination
Declination
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Declination in Washington, D.C. over the past 250 years
Magnetic declination and polar wander
Latitude and magnetic inclination
Inclination
Polar wonder or moving continents
Units: gauss, but are generally reported in nanoTesla (1nT * 100,000 = 1 gauss). The Earth's magnetic field intensity is roughly between 25,000 - 65,000 nT (.25 - .65 gauss)
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External variation
Earths magnetosphere
The Solar System is a dangerous place to live Large amounts of radiation (cosmic rays, solar wind) are present in interplanetary space On Earth, we are protected from these harmful cosmic rays by our atmosphere and magnetosphere. Earths magnetic eld forces these cosmic rays to deect away from Earth
Paleomagnetism recorded in Earths rocks
Paleomagnetism recorded in sediments
The eld reverses polarity A reversal recorded in 16 myr old volcanic rocks
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The field reverses polarity
The field reverses polarity
Computer model (Glatzmaier-Roberts)
Computer model (Glatzmaier-Roberts)
http://www.psc.edu/research/graphics/gallery/geodynamo.html
The field reverses polarity
The field reverses polarity
some reversals occurred within a few 10,000 years of each other, and there are other periods inour past where no reversals occurred for tens of millions of years
so The magnetic eld results from the circulation of liquid iron alloy of the Earths outer core (an electrical conductor)behaves like an electromagnet or dynamo Dipole eld Magnetic declination, currently dips ~11 to the Earths rotational axis Latitude and magnetic inclination
The Earth's geomagnetic eld varies in both space and time. The geomagnetic eld measured at any point on the Earth's surface is a combination of several magnetic elds generated by various sources. These elds are superimposed on and interact with each other. More than 90% of the eld measured is generated internally in the Earth's outer uid core. This eld is referred to as the Main Field. The remaining ~ 10% arises from electrical currents owing in the ionized upper atmosphere, and the elds induced by currents owing within variations in the Earth's mantle and crust.
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So, what do we know about the Core - The core of the Earth accounts for about 30 % of the total mass of our planet - The inner solid core is crystallizing from the liquid outer corecms per year! - The crystallization of the inner core is responsible for compositional convection in the liquid outer core, that is the engine which generates the Earth's magnetic eld - The heat released ows to the surface, driving all the living geological processes of the Earth, including plate tectonics, volcanism and earthquakes.
The Core is mainly made of Fe -Ni, but it can't be pure Fe, because its density is too low. So the Core must contain some light elements, and the most likely candidates are sulfur, oxygen, carbon and silicon, but the real composition of the Earth's core remains one of the major unsolved problems Radius = 6370 kilometers = 4000 miles
The density and the pressure of the Core are known quite accurately (within a percent), but the temperature is unknown, with estimates ranging from 4000 to 8000 K.
Radius = 6370 kilometers = 4000 miles
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