Week 2- Origin, life cycle and sediments of the ocean Flashcards
When was the beginning of the universe?
14 billion yrs ago
When was earth formed?
4.5-4.6 bya
What is Accretion?
Bits come together to form the earth
How do we know that the earth is that old?
Rocks
Uranium led dating
Earth’s first atmosphere
Mainly H and He stripped solar wind
Earth’s second atmosphere
- Mainly CO2 and water vapour (H,N and sulphur-based gases)
- Formed by outgassing (burping gases to the surface)
- earth starts to become solid but is not yet liveable
Ocean formation
- 3.8-4.2 Ga
- water vapour cools and forms droplets, rain falls to earth and fills depressions
Early life on earth
Cyanobacteria (blue green algae)
3.5 Ga
Great oxidation event
Cyanobacteria photosynthesize and produce O2, creating the third atmosphere
2.4 Ga
Where did life most likely originate?
At hydrothermal vents in the early ocean
Why did life mostly originate in hydrothermal vents?
Protected from meteorites that hit the ocean surface
Warm, alkaline environment (ideal conditions)
Created self-assembling protocells
What type of organism lived at hydrothermal vents?
Extremophiles (achaea)
- live in extreme conditions and metabolize sulphur
Stromatolites importance
Led to the accumulation of breathable oxygen and evolution of multicellular life
What is the Wilson cycle?
Explains how oceans are created and destroyed
400 million year cycle
Which stages of the wilson cycle are opening the basin?
Stage A, B and C
What stages of the wilson cycle are closing the basin?
Stage D, E, F
Wilson cycle Stage A: Embryonic
Rifting: earth’s crust is stretching and cracking; fissures form, faulting occurs
- rift valley forms
- subsidence (early stage of ocean formation)
Example of Stage A
East Africa rift
Wilson cycle Stage B: Juvenile
Oceanic rift zone: going to be an ocean forming
- widening of rift valley
- crust is thinning
- subsidence and connection to ocean (ocean water comes in to fill rift valley
Example of stage B
Red sea
Wilson cycle stage C: Mature
- Continued lateral spreading of rift valley
- Widening generation of new ocean crust
- Increasing sedimentation
- Geologically passive margins
Example of stage C
Atlantic
*every year is gets wider
Wilson cycle stage D: Declining
- Convergence (ocean starts getting smaller)
- Increasing subduction
Example of stage D
Pacific
*pacific plate is sub ducting underneath the Asian plate