Introduction to the Geosphere Flashcards
Define the geosphere
Dense, primarily solid part of the earth that consists of rocks and overlaying sediment
The elevation of the Earth’s surface has a bimodal distribution, with one peak associated
with the continents, the other associated with the ocean floor. What explains this?
Variation in density and thickness between oceanic and continental crust
Composition of the continental crust
granitic on average, with feldspar and lighter elements; felsic
Composition of the oceanic crust
Maific, rich in Mg and Fe, not in silica
What was the Challenger
First scientific analysis of Deep Sea
If we look at the amount of sediment on the ocean floor, how old would the earth be, at present rates
260Ma
Why was continental drift hypothesized
The same fossils and land forms were found on different continents
Who proposed continental drift
alfred wagner
Who revamped the continental drift theory in the 60x
Arthur stahler
What was the alternative theory to continental drift
land bridges
Who hypothesized land bridges
Eduard Seuss
What is the formula used by SONAR
V = 2d/t
What does SONAR stand for
SOund Navigation and Ranging
What other instrument besides sonar was used to map the surface of the ocean
Magnetometers
Who did the first expedition using sonar to map the bottom of the ocean, and what was the result
Heezen and Tharp in 1957
they produced the first publicly accesble map of the ocean floor
Who hypothesized that the earth was layered
Andrija Mohoveric
Who hypothesized that the outer core was liquid
Inge Lehman
What three things characterize the mid oceanic ridges (apart from the fact they are ridges)
- Characterized by high heat flow
- seidment thickness and age increased as you move further away
- opposite dipole strips move like a bar code away from them
What do the magnetic anomalies around oceanic ridges show
That the earth occasionally switches it poles
What generates the lithosphere
Generated by volcanism at mid oceanic ridges
How are the plates recycled, and what are these places called
One pushes underneath another plate, getting absorbed into the mantle. Called subduction zones
Why are there continents
They are composed of lighter material and float on top of the mantle like an iceberg
Why are land and oceanic plates of different composition
The oceanic plates are made from uniformly melted mantle that has a more uniform chemistry. Land plates are made of many different cycles of partial melting, and are not uniform
Why are there mountain belts
continents crashing into each other, or by large scale volcainc eruption
What is the subduction zone
where one plate goes under another, and gets absorbed into the mantle
How hawaii exists
It is a mid plate plume of magma
Does not move, the mantle jsut moves over top
It is a hot spot
Why is the oceanic crust so young?
Sediment keeps getting recycled into the mantle
Why are oceans shallower in the middle
thermal subsidence (definition on another slide on this deck)
define thermal subsidence
The oceanic lithosphere becomes thicker and denser as it cools. therfore, the middle of the ocean will be thickest, because it is the coldest
Where are plates generated at
Mid oceanic ridges
What is the composition of the mantle
ultramafic
Define viscoelestic
Having both the properties of a solid and a liquid (the mantle is like this)
Where are plates returned to the mantle
Subduction zones
What explains mountain belts that reside in the interior of continents (e.g., Himalayas)?
Collision of continental crust with continental crust
Why is continental crust so old relative to oceanic crust?
Oceanic crust is continuously being recycled into the mantle at subduction zones, whereas
continental crust is too buoyant to undergo this process
What explains the compositional difference between continental crust, oceanic crust, and
the mantle?
Partial melting
Which of the following observations did Alfred Wegener use to support his continental drift
hypothesis?
a) The observation that the mid-oceanic ridge is a long, linear volcano
b) The observation that oceanic crust has a barcode-like magnetic signature
c) The observation that the age of oceanic crust increases away from spreading ridges
d) The observation that the age of basal sediments overlying the oceanic crust increases
away from spreading ridges
e) None of the above
e
Why was Wegener’s continental drift hypothesis rejected when he proposed it initially?
The main reason was lack of a viable mechanism.
Why does the ocean floor increase in depth from mid oceanic ridges towards the adjacent
continents?
thermal subsidence
