Land Air and Ocean

Question 1

How did the early solar system form?

Answer 1

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’

Question 2

What is the origin of the land (crust) on our planet

Answer 2

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.

Question 3

What was the Hadean crust like?

Answer 3

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)

Question 4

Where did continental felsic material come from?

Answer 4

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!

Question 5

What is earth’s oldest material?

Answer 5

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.

Question 6

What are old continents called?

Answer 6

Seeds! Today they’re called shields. They grew by accretion, and have distinct edges that have been added to - shart contacts called ancient protocontinents.

Question 7

What is the 1st atmosphere?

Answer 7

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.

Question 8

what are the northern lights?

Answer 8

Solar winds interacting with our atmosphere! cool

!

Question 9

Why don’t solar winds strip earth of its atmosphere now?

Answer 9

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!

Question 10

Describe Mars.

Answer 10

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?

Question 11

Describe Earth’s 2nd atmosphere?

Answer 11

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

Question 12

Describe the 3rd atmosphere?

Answer 12

(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

Question 13

What is the evidence for low oxygen in archaean?

Answer 13

1) Few oxidized iron minerals
- pyrite found and continental desert rocks are green (unoxidized)
2) Limestone questions

Question 14

What is the difference between oxidized/anoxic iron?

Answer 14

Oxygen rich: hematitie and magnetite

Oxygen poor: pyrite, iron sulfide

Question 15

How is pyrite found in archaean vs today?

Answer 15

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

Question 16

What is the question of limestone?

Answer 16

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.

Question 17

What is the evidence of anoxic to oxic atmosphere?

Answer 17

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

Question 18

Where does iron in BIFS come from?

Answer 18

Erosion of continental rocks (washing iron into oceans

Introduction of iron at ocean ridge systems (underwater anoxic world)

Question 19

What would have happened to FE in the early archean? What changed?

Answer 19

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.

Question 20

What causes red layers to precipitate?

Answer 20

Oxygen, Biology Photosynthesis (rusted out of the ocean)

Question 21

What characterizes non red layers?

Answer 21

low iron oxide, high silica (which comes from erosion of felsic continental rocks)

Question 22

What do bands in BIFs represent?

Answer 22

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)

Question 23

When was iron all rusted out of the ocean?

***

Answer 23

1. 8Ga, now o2 can escpae to the atmosphere !! this turned all rocks red!
   * **

Question 24

How did the oceans begin?

Answer 24

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.

Question 25

What is the problem with comets bringing water?

Answer 25

The composition is different. Comets contain heavy water with deuterium hydroden. D20 2H20.
Most water is protium water, regular h20.

Question 26

What is comet Hartley?

Answer 26

at the hershel space observitory, found a comet that contains ocean like water (less D20). Came from KUPIER belt (heavy water comets) NOT oort cloud where lighter ones are usually found.

Question 27

Why does Hartley appear to be in the wrong spot?

Answer 27

Lighter comets should be further out. But when jupiter and saturn moved around towards the sun, it rearranged everything with its gravitational force, and could have brought lighter comets with it.

Question 28

What is the Isua complex and what does it tell us?

Answer 28

Greenland, 3.8 Ga, has sediments and pillow lavas that prove water on theplanet (can only form under water - very specific structure)
- have a tail from which they are injected, bulbous top thats only formed underwater

Question 29

Describe how zircon crystals from jack hills dated at 4.4 GA create a problem for our original understanding.

Answer 29

Formed in granite, meaning that earth would have a solid surface for injection.
Isotopic signatures from these crystals indicate water from WAY back, maybe life has been around even longer than we thought!
- hinting that water had interacted with what was generating the granite