week 5

Question 1

the hadean eon

Answer 1

• period before our rock record (hell-like)
• earth formed around 4.57 Ga and differentiated into core and maantle by 4.5 Ga
• much of surface was magma ocean until 4.4 Ga

Question 2

what eon what collision with a mars-sized protoplanet (4.5 ga)

Answer 2

hadean:
- created a magma ocean
- ejected material caught in orbit and formed earths moon

Question 3

hadean atmosphere

Answer 3

• no life forms
• colliding comets contributed some h2o
• gas from volcanoes
• denser than now
  water vapor, nitrogen, methane, ammonia, hydrogen, co2, so2`

Question 4

what is the oldest geologic material found

Answer 4

zircon: 4.4 ga

Question 5

what is the oldest crustal rock found

Answer 5

4.03 or 4.28 Ga

Question 6

oldest sedementary rock found

Answer 6

3.58 Ga

Question 7

no preserved rocks older than 4.28 Ga?

Answer 7

late-heavy bombardment of earth and its moon by meteorites destroyed all earths surfaces

Question 8

archean eon

Answer 8

= beginning
- end of hadean to 2.5 Ga (proterozoic)
- first abundance of preserved crustal rocks plate tectonics began during or just before

Question 9

describe the early plate tectonics

Answer 9

• early crust probs made up of mafic igneous rocks fromed as island-arcs and hot-spot volcanoes
• partial melting of basaltic crust with h2o created felsic rocks
• small blocks of buoyant crust develop
• rifting led to flood basalts
• erosion produced sediments

Question 10

how were protocontinents formed

Answer 10

• archean eon
• by collisions of buoyant blocks: volcanic arcs, hot spots and sedimentray debris were sutured together as the first continents

Question 11

what eon was the first sign of life

Answer 11

archean:
- around 3.2 Ga (oldest fossils)
- photosynthesesis started in late archean
- from deep, dark ,hot water vents: heat-loving bacteria or prokaryote archaea exist in extreme conditions

Question 12

archean strata contain stromatolites

Answer 12

• first large fossil structures: layered mounds of sediment
• alternating ayers of cyanobacteria and sediment settling from water

Question 13

proterozoic eon.

Answer 13

= early life
- around 2.5 Ga to 542 Ma
- several rounds of super-continent assembly and rifting
- 90%of continentalcrust fromed by. iddle proterozoic

Question 14

cratons

Answer 14

cold, stable , interioir regions of continental crust
- consist of distinct orogens, block s and terrains,
- proterozoic eon
- parts fo a craton: shield, platform, basement