Geology Unit 3

Mid-Atlantic Ridge is...

Divergent

Discuss divergent boundaries.

Divergent boundaries are boundaries where the tectonic plates are moving away from each other. Mid-ocean ridges occur in divergent plates and new crust is formed. There are lots of shallow earthquakes and lots of volcanos are formed.

Isostasy

Explains the relative elevations that materials of different density & thickness reach at equilibrium with gravity while floating on a fluid (lesser density and thicker material will flow higher above fluid it is floating upon)

Seamount

Underwater mountains that rise hundreds of feet from the seafloor. They are generally extinct volcanoes that, while active, created piles of lava that sometimes break the ocean surface.

Mantle Plume

A persistent upwelling of hot material moving upward from the deep mantle to the crust

Hot Spot

A stationary volcanic center located above a mantle plume

Mantle Convection

The energy that comes from the Earth's internal heat

Mesosaurus

The greatest evidence of Pangaea and continental drift. It only swam in fresh water yet remains were found in SA and Africa which means they had of once been connected if there wasn't a land bridge.

(third essay question) ( age of ocean crust evidence) Note that...

all oceanic crust on Earth is younger than about 200 million years. This is actually surprising given that the Earth was formed about 4,600 million years ago and there are areas of the continents where the rocks are known to be almost 4,000 million years old. The oceans are young because old ocean crust becomes quite dense and tends to be subducted back into the mantle. Thus it does not hang around on the surface of the Earth very long. Continental crust is relatively quite light, both when it is young and when it is old, so it tends to stay at the surface nearly forever.

Alfred Wegner

came up with the idea of Pangaea (all continents once being one)

Collision=

continental-continental

The Himalayas are...

continental-continental

Convergent means that earthquakes are generally

deep and powerful.

At divergent plate boundaries..

earthquakes tend to be weak and shallow

High Magnetic Dip equals...

high latitude

Low Magnetic Dip equals...

low latitude

Continental volcano=

ocean-continent

Trench=

ocean-continent, ocean-ocean

Cascade range is...

ocean-continental

Convergent plates where you find volcanic islands=

ocean-ocean

Convergent plates where you find subduction=

ocean-ocean, ocean-continent

Transform plate boundaries have...

shallow and powerful earthquakes.

Magnetic Dip

the angle/degree to which magnetic particles point into the earth, directly related to the latitude at which it points

With ocean ocean..

the older plate will subduct because it's cooler and denser

(second essay question) Before the theory of plate tectonics the concept of continental drift was proposed in the early 20th century. Many lines of evidence were cited to support continental drift including world maps, geology and evidence of past climates. Explain how each of these lines of evidence was used to support continental drift.

1) The match of the continental coastlines is a big factor. The matching of them basically shows that the continents we're on today actually perfectly align together which means that the only explanation is them once being together. 2) There is paleontologic evidence that also points to the theory of continental drift. The prime example is with the mesosaurus. The mesosaurus (which dwelled in freshwater) had fossils found on the east side of South America and on the west side of Africa. People thought maybe it was a due to a land bridge that they could've walked across, natural rafts, or maybe that they swam. None of those ideas were plausible though which leads to the fact that continental drift occurred and that SA and Africa were once connected in those spots. 3) There is also paleoclimatological evidence. Rocks deposited and eroded by glaciers that existed 300 million years ago are now distributed across the globe, some at very low latitudes where glaciers would seem unlikely. Continental drift serves as an explanation for why that happened. 4) Geologic structures and rock types could be traced from one continent to another across what is now a wide stretch of ocean. When Pangaea was reconstructed these rocks lined up perfectly with one another.

(third essay question) What are 3 lines of evidence that verify sea-floor spreading? Explain how each verifies seafloor spreading. What is the main mechanism causing the spreading of the seafloor? How does it work?

1st line of evidence: Magnetic anomalies. They found stripes of seafloor where magnetic properties of seafloor were of normal and reverse polarity. Vine and Matthews used this data as evidence indicating that new seafloor was being formed at mid-ocean ridges, where they become magnetized, and move away from each other on both sides of the ridge (aka seafloor spreading). 2nd line of evidence: The Age of Ocean Crust. The youngest seafloor is at mid-ocean ridge and it becomes older with increasing distance from ridge. 3rd line of evidence: The depth of the ocean crust versus the age. As ocean crust gets older, gets cooler, and more dense, it sinks further and deeper into the asthenosphere. Younger ocean crust is warmer and less dense thus ridges higher in asthenosphere. That is why old ocean crust found at deeper depths in the ocean. Thus the farther way from mid-ocean ridge the deeper the depths. The mechanism is mantle convection and its when hot matter from the mantle rises causing plates to form and diverge. Where played converge, a cooled plate is dragged under the neighboring plate.

Island Arc

A type of archipelago, often composed of a chain of volcanoes, with arc-shaped alignment, situated parallel and close to a boundary between two converging tectonic plates

Continental Drift

Continental drift is the movement of the Earth's continents relative to each other, thus appearing to "drift" across the ocean bed.

Where does destruction of Earth's crust take place?

Convergent Boundaries

Discuss convergent plates specifically

Convergent plates are two plates that are colliding or sub-ducting. There are three types of convergent plate boundaries. Those are continent-continent, continent-ocean, and ocean-ocean. The process going on with convergent plates are that two plates are colliding or subducting (depending on the crust). If they're subducting you get crust entering the mantle and being recycled and volcanos being created. Earthquakes are prevalent in this plate boundary and are especially deep where subduction occurs.

Harry Hess

He Proposed Seafloor Spreading (new ocean crust created at rifts in the middle of ocean basin - spreads laterally away from rift and replaced by new crust

(fourth essay question) Why does the ocean crust show a sequence of magnetic polarity changes symmetric across the mid-ocean ridge? Explain fully. What is the average rate of seafloor spreading in cm/yr (100,000 cm = 1 km), if the age of the magnetic anomaly shown below is 4 million years old at point A? Show your work.

It shows that because new seafloor was being formed at mid-ocean ridges, where they become magnetized, and move away from each other on both sides of the ridge. The average rate of seafloor spreading would be....

(second essay question) Why was this concept (continental drift) almost universally rejected despite many lines of evidence supporting it?

It was rejected because Wegener couldn't provide a plausible mechanism to explain how the continents could have drifted apart. They thought it was too far-fetched and contrary to the law of physics.

Vine & Matthews

Matthews and Vine discovered seafloor spreading and came up with a plausible theory regarding it.

Magnetic Anomaly

Mid-ocean Ridge (both sides of the ride were normal polarity, further away from ridge went from normal to reverse so on...)

Japan is...

Ocean-ocean

Plate Tectonics

Plate tectonics is the theory that Earth's outer shell is divided into several plates that glide over the mantle, the rocky inner layer above the core. The plates act like a hard and rigid shell compared to Earth's mantle.

Transform Boundary

Plates that slide horizontally past one another

(second essay question) Just know that...

The concept of continental drift was resurrected some 30 years later in the late 1950s and early 1960s as the concept of seafloor spreading was proposed.

(first essay question) How do the differences between continental and oceanic crust affect the ways plates interact? Why does lithosphere with continental crust ride above lithosphere with oceanic crust? Why is the area around a divergent boundary higher than the surrounding seafloor?

The continental crust floats on denser mantle and continental crust is less dense than oceanic crust and therefore rides high. Oceanic crust= more dense and thinner. Continental crust= less dense and thicker. -Lithosphere with continental crust always rides above the lithosphere with oceanic crust because oceanic crust is more dense and thicker. -Because it is where adjacent lithospheric plates spread apart from one another, and new lithosphere is produced.

Subduction

The process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate and sinks into the mantle as the plates converge. Regions where this process occurs are known as subduction zones.

Pangaea

The super continent. It was all of the continents connected at one point.

Trench

They're the deepest point in the ocean at convergent boundaries with subduction.

San Andreas is...

Transform

Discuss transform boundaries.

Transform boundaries are when tectonic plates are moving horizontally past eachother. No volcanoes occur here because there's no subduction occurring. There are severe and shallow earthquakes that occur here.

Convergent Boundary

Where adjacent lithospheric plates come together, either colliding or one subducting beneath the other

Divergent Boundary

Where adjacent lithospheric plates spread apart from one another and new lithosphere is produced

Seafloor Spreading

a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge. Helps explain continental drift in the theory of plate tectonics.

Divergent plate boundaries tend to be...

weak and shallow.