Lec 3: Plate Tectonics Flashcards
The Earth’s evolution is divided into time periods. What are these based on? What do they correspond to?
The time periods are based on fossil/rock record. They correspond to changes in Earth’s climate, surface, or life forms.
How are absolute dates determined?
From radiometric dating of IGNEOUS rocks.
How is relative dating determined?
From the relationship between rocks
What are the 3 types of rocks and what do they tell us about dating?
- igneous: cooled magma. Allow us to date most accurately, give us ABSOLUTE dates.
- sedimentary: formed from chemical precipitates or fragments of earlier rocks. Tell us about the relative ORDER in which events occured.
- metamorphic: formed from the application of heat or pressure to igneous or metamorphic rocks.
radiocarbon dating works for things up to …. years old
50 000 years old
How does radiometric dating with carbon work?
C-12 and C-13 are both stable carbon isotopes. C-14 on the other hand is unstable, meaning it decays for up to 50 000 years. By measuring the amount of C-14 in a rock, we can determine its age. Less C-14 = older rock.
How do we determine the absolute age of rocks that are older than 50 000 years old?
Minerals within the rocks contain small amounts of unstable isotopes. By measuring the decay of these elements we can determine their absolute age. Measure ratio of radioactive parent to stable daughter isotopes.
What is the Principle of Superposition?
newer sediment is continually deposited on top of previously deposited sediment.
In which type of rock are fossils most abundant?
Marine sedimentary rocks
Can we use the thickness of sedimentary layers to estimate how much time a layer represents? Why?
No.
- sediment accumulation is slower in the deep-sea
- storms can remove meters of sediments on beaches
- rocky coasts may see very little sediment accumulation
When did Earth form? What did it form out of?
4.54 billion years ago out of a solar nebula
What is the Goldilocks Zone?
The habitable zone around a star. From Earth to Mars.
What was Earth like during the Hadean Eon (4.5 to 4 Ga ago)
- molten
- constantly bombarded by asteroids and comets
- the moon was formed when a small planet collided with Earth
How was the Earth’s core created?
Earth was bombarded by smaller bodies, heating the Earth. Gravitational contraction also heated Earth. The Earth thus melted, and the heavier, iron-rich fraction of this liquid settled at its center.
What was Earth like 4.4 Ga ago?
- It had a core, mantle, and crust.
- core = solid iron
- outer core = liquid iron
- mantle = partly melted magma
- maybe thin skin of solid rock
What was Earth like by the end of the Hadean (4 Ga ago)?
- Earth cooled enough that rocks + oceans began to form
- steam in atmosphere cooled + fell, created oceans
- first continents begin to form
What is the Archean eon associated with?
Life and plate tectonics!
- liquid water is prevalent
What is the plate tectonics theory?
Idea that the Earth’s crust floats atop a liquid mantle.
Who proposed the continental drift theory?
Alfred Wegener in 1915
Describe the Earth’s structure.
1) Core
- inner core is solid, outer core is liquid and source of magnetic field
- rich in iron (unlike Jasmine)
2) Mantle
- behaves plastically
- rich in silicon and oxygen
3) Crust
- rich in silicon and oxygen
What are tectonic plates made up of?
crust + upper mantle
What are the different kinds of crust on Earth?
1) Oceanic
- thin, dense, young
- more iron
2) Continental
- thick, buoyant (less dense), old
Which type of crust sinks under the other?
Oceanic crust sinks under continental crust
What are differences in crust densities due to?
chemical differences
What causes plates to move?
convection currents in the mantle
Do plate boundaries correspond to continent boundaries?
no.
Where can divergent boundaries occur?
They can form WITHIN continents. They produce rifts. New crustal material forms oceanic crust.
Where do most active divergent plate boundaries occur?
Between oceanic plates, called mid-oceanic ridges.
This is called seafloor spreading.
What is the longest mountain range in the world?
the Mid-atlantic ridge
What are the 3 types of plate collision?
- continent-continent
- continent-oceanic
- oceanic-oceanic
What does continent-continent collision create?
Very large mountain ranges!
Both plates are too buoyant to be subducted.
What does continent-oceanic collision create?
Mountain range on continental plate + trenches!
Denser oceanic plate is subducted
What do transform boundaries do?
result in earthquakes, creating faults.
How have plate tectonics promoted the biodiversity of organisms?
changes in biotic and abiotic factors create new habitats and eventually new species.
Are the evolution of life and the evolution of Earth connected?
Yes!
