Land Air and Ocean Flashcards
How did the early solar system form?
the Nebula Hypothesis states that our solar system formed out of a slowly collapsing cloud of dust and gas, the center is the sun, and everything else was a disk where planets are formed through accumulation.
Hydrogen were forcd otgether to form helium, causing nuclear fission and the sun ‘switched on’
What is the origin of the land (crust) on our planet
less than 1% of earth’s volume.
Oceanic and continental (thicker)
Under the crust is pretty solid, not a ‘magma ocean’ as some think.
melting (partial) occuts to give us magma.
Oceanic: basaltic, Mafic (magnesium iron) - low silica content, higher density
Continental: MOSTLY granitic, felsic (felspar and silica)- high silica, low density.
What was the Hadean crust like?
as rocks smash, kinetic energy builds up and makes it melt. Concentrating radioactive material making it massive nuclear pillar.
Magma ocean ! but then rafts would form called KOMATITES, more dense than basalts, but rich in iron. komatites driven around surface by mantle convection, eventually forming a basaltic skin (oceanic crust)
Where did continental felsic material come from?
When oceanic plates subduct, partial melting occurs below volcanos to prodce felsic magmas that are lighter in density.
hot magma rises up- is less dense, and forms felsic volcanos!
What is earth’s oldest material?
Acasta Gneiss 4.04 Ga in canada!
also
Jack Hills conglomerate and zircon in Western Australia found from eroded granitic material at 4.4 Ga
- in the conglomerate were the very old zircon crystals.
This indicated earth had a solid surface to insert the granite into.
What are old continents called?
Seeds! Today they’re called shields. They grew by accretion, and have distinct edges that have been added to - shart contacts called ancient protocontinents.
What is the 1st atmosphere?
Out of the nebula!
Hydrogen and Helium (nebula composition?)
THis was removed as the sun ‘switched on’ and the solar wind was activated. Light elements would have been blown into space.
what are the northern lights?
Solar winds interacting with our atmosphere! cool
!
Why don’t solar winds strip earth of its atmosphere now?
it has a metallic core that keeps a magnetosphere (solid inner core with rotating mobile liquid core to create a DYNAMO effect. This generates elecricity (magnetic force lines)
These charged particles move around magnetic flux lines and you see them around the poles. This protects earth from solar winds!
Describe Mars.
A planet with no magnetosphere! very little atmosphere. Evidence of liquid water (river systems deposits, evaporite minerals), suggesting a thick atmosphere at one point.
Maybe mars had ‘patches’ of a magnetosphere?
Perhaps the metalic core solidified completely?
Describe Earth’s 2nd atmosphere?
Due to Volcanos !!
Outgassing of water, CO2, hydrogen nitrogen sulphur based gases and chlorine
(mostly water 60%)
co2 about 10-40%
today atmosphere is mostly nitrogen.
This is evidence that the interior of our planet is hot
Describe the 3rd atmosphere?
(our atmosphere today)
Oxygen generation happens in 2 ways
1) photochemical dissociation of H20 into O and H atoms from UV radiation creating Ozone layer
2) photosynthesis of c02 by biology
What is the evidence for low oxygen in archaean?
1) Few oxidized iron minerals
- pyrite found and continental desert rocks are green (unoxidized)
2) Limestone questions
What is the difference between oxidized/anoxic iron?
Oxygen rich: hematitie and magnetite
Oxygen poor: pyrite, iron sulfide
How is pyrite found in archaean vs today?
archaeon: As grains (DETRITAL) in sedimentary rocks (assisted by bacteria)
today: not like this due to rapid oxydation assisted by bacteria. it just looks like nasty yellow sludge because of microbes
What is the question of limestone?
Evidence indicated a high concentration of C02 = carbonic acid - acidified oceans (oceans are great buffers for co2). Carbonic acid dilutes carbonate so harder for corals to produce shells, thats why you see LESS CARBAONATE LIMSTONE rocks because of high acidity, inabiility to precipitae limestone in archean.
What is the evidence of anoxic to oxic atmosphere?
BIFs (banded iron formations) with chert (silica) alternating with iron oxides (hematite and magnetite)
Bifs are deposited in the transition between oxic and anoxic
Can be traced 100s of kms, shallow oceans flooding margins of continents. High sea levels and shallow marine environemnt.
Earliers 3.7 Ga, abundant at 2.4 Ga rare after 1.8 Ga
Where does iron in BIFS come from?
Erosion of continental rocks (washing iron into oceans
Introduction of iron at ocean ridge systems (underwater anoxic world)
What would have happened to FE in the early archean? What changed?
It would have dissolved in the oceans SO what changed WAS stromatolites.
Stromatolites are recorded 3.45 Ga, photosythetic cyanobacteria, look like mats.
Organo sedimentary structures!
Stromatolites are common when BIFS are common, Bandadine is found close to stromatolites.
What causes red layers to precipitate?
Oxygen, Biology Photosynthesis (rusted out of the ocean)
What characterizes non red layers?
low iron oxide, high silica (which comes from erosion of felsic continental rocks)
What do bands in BIFs represent?
SEASONAL CHANGES!
photosynthesis slows in winter months
summer: iron in bands precipitate more iron out of the ocean
winter: more erosion, less sun, more silica (chert)
When was iron all rusted out of the ocean?
***
- 8Ga, now o2 can escpae to the atmosphere !! this turned all rocks red!
* **
How did the oceans begin?
a) water from volcanos
b) comets with water!
- space deep impact probe (shows ice is common in solar system!)
initially too hot for condensation! but temps would have dropped and then it would have rained for thousands of years.
initially would have been fresh, salt added from erosion of rocks and introduction of minerals during volcanic events.
