Origin Of Earth’s Structure Flashcards
What step 1 of the nebula theory storyboard on the formation of the solar system?
A giant cloud (nebula) or molecular hydrogen and dust collapses - possibly when hit by a shock wave from a nearby exploding star (supernova event). Cloud becomes denser
What step 2 of the nebula theory storyboard on the formation of the solar system?
As the size of the cloud nebula decreases, the rate of rotation increases, causing the hot gaseous cloud to flatten out into a protoplanetary disc.
Materials are drawn towards the centre by gravity. It becomes so hot and dense that it triggers nuclear fusion, increasing the temperature of the surface of the star which becomes visible
What step 3 of the nebula theory storyboard on the formation of the solar system?
Accretion of gas into the star continues for another 10 million years
What step 4 of the nebula theory storyboard on the formation of the solar system?
The protoplanetary disc cools allowing the formation of small grains of rocks and ice. Electrostatic and gravitational forces bring the grains together into a vast number of small bodies called planetisimals, a km or so across. The planetisimals accrete to form embryonic protoplanets about the size of the moon
What step 5 of the nebula theory storyboard on the formation of the solar system?
The protoplanets nearest to the central star collide to form a small number of terrestrial planets. Thus may take up to a billion years to occur
What step 6 of the nebula theory storyboard on the formation of the solar system?
Giant planets may have their own spinning, flattened accretion discs of captured hydrogen and helium, which is then deposited onto the planet’s surface, whilst solid material with the disc accretes to form moons
What step 7 of the nebula theory storyboard on the formation of the solar system?
The leftover planetisimals which do not form planets are the asteroids and meteorites, which are asteroid fragments that provide a great deal of information about the formation of the solar system. Comets are planetisimals which form furthest from the star
What step 8 of the nebula theory storyboard on the formation of the solar system?
Our moon probably formed when a protoplanet obliquely impacted with the young earth between 30-50 million years after the formation of the solar system
What is an accretion disc also known as?
A protoplanetary disc
What is the difference between an asteroid and a meteorite?
Meteorites are asteroids that have reached the earth’s surface
Where do most asteroids come from in our solar system?
Kuiper belt
Why do most meteorites that enter earth’s atmosphere not actually reach the surface?
Most burn up
What are chondrules?
Chondrules are found in chondrites.
Molten droplets (of olivine - ultramafic) formed at high temperatures in the early solar cloud
Rounded –> molten droplets
What are chondrites?
Contain chondrules.
Most abundant meteorite found on earth —> 85%
Chemically similar to the sun and the composition of the whole solar system.
Contain iron, Magnesium, silicon, oxygen –> ultramafic
What are the three types of meteorite? (Chondrites)
Iron, stony, carbonaceous
What are the characteristics of iron meteorites?
Made of iron and nickel
What are the characteristics of stony meteorites?
Made up mostly of silicate minerals (mafic –> pyroxene, Olivine, some feldspars)
What are the characteristics of carbonaceous meteorites?
Contain organic material (including carbon and WATER)
Key to the start of life.
How do iron meteorites help us interpret earth?
Similar composition to the core
How do stony meteorites help us interpret earth?
They contain pyroxene or olivine.
Very similar composition to the mantle
How do carbonaceous meteorites help us interpret earth?
Help us understand the whole composition of the earth
What causes impact craters?
Meteorite or asteroid impacts
What is the difference between impact craters on the moon and on the earth?
Moon - very visible, no rock cycle
Earth - less visible because of vegetation, erosion, and tectonic movement. Earth cycles rock (rock cycle)
What features of craters are evidence that they were caused by asteroid impacts?
- Circular depression with a raised rim
- Rock strata are tilted
- shocked Quartz
- rocks at depth may be brecciated
- inverted strata
What was the tunguska event?
A suspected asteroid impact in Russia with a 1000km radius on June 30th 1908.
Shock wave hit at 60km from ground (knocked people unconscious)
Only investigated in 1921 by Leonard kulik
15km/s when entered earth’s atmosphere
Found lonsdaleite (meteorite origin)
Massive forest fires
What are the two main sources of earth’s heat?
Residual (left over) heat from the formation of the solar system
Radioactive decay of unstable isotopes
How does the formation of the earth produce heat (now)?
Upon collisions, kinetic energy is transferred to heat energy. Lots and lots of collisions formed the earth
How much of earth heat came from the formation of the earth?
⅓
How does radioactive decay produce heat to the earth?
Unstable parent isotope decay to produce stable daughter isotopes. This creates heat energy.
Largely happens in the mantle.
Examples of unstable ions in the mantle include: thorium, uranium, Potassium
How much of the earth heat is produced by radioactive decay?
⅔
What is meant by the term geothermal gradient?
The change in temperature and rate of temperature change with depth in the earth
What is the current theory about heat transfer and its source?
Heat flow
What is the outdated theory about heat transfer and its source?
Convection cells
Why do we believe heat flow, the current theory about heat transfer?
- the transfer of heat from the interior of the earth to the surface
- we know this happens because we can measure thermal flux
- thermal flux is greater in oceanic plates due to it being thicker
Oceanic - 100mWm-²
Continental - 65mWm-²
What is heat flow, the current theory about heat transfer?
Heat is transferred to the surface by:
Conduction - transfer of energy from atom to atom without movement
Convection - warm/hot materials expand, become less dense and rise, energy transfers then falls (convection cells)
Advection - transfer of energy through liquid, sea water. Only happens close to the surface
What are convection cells, the outdated theory of heat transfer?
Convection does happen in the mantle and are responsible for some heat transfer.
Plates are moving faster than convection cells —> must be another cause
What is a lithophile?
“Rock loving”
Elements that combine readily with oxygen to form low density compounds, which therefore remain near the surface of the earth.
Lithophiles commonly form oxides.
They are very reactive elements.
Electrolysis is needed to extract the metal from the ore.
What is an atmophile?
“Gas loving”
Including volatiles. Occurs in liquids or gases at the temperature and pressure conditions found on or above the earth surface.
Crustal abundance was reduced by loss from early atmosphere.
Nitrogen was released by the oxidation of early ammonia as photosynthesis developed
What is a chalcophile?
“Ore loving”
Elements that combine readily with sulfur to form higher density sulfides. These occur deeper than the lithophiles, but not as deep as the siderophiles.
Crustal abundance is increased by the secondary enrichment processes.
Easily extracted from ores by combustion with carbon in the form of the fuel, coke
What is a siderophile?
“Iron loving”
High density transition elements which combine more easily with iron than oxygen. Forming dense compounds.
These descend to lower layers of the earth.
Rare in the Crust.
Ores are mined from eroded ultramafic rocks of deep origin
