Chapter 2 - Plate Tectonics and the Structure of Ocean Basins

core

inner most layer of the earth

Mantle

(1) the semiliquid region between the crust and the core of Earth

(2) the outer layer of tissue that secretes the shell of molluscs

Crust

Earth's outermost layer.

basalt

The dark-colored rock that forms the sea floor, or oceanic crust.

Granite

The light colored rock that forms most of the continental

crust.

continental drift

the movement of continental masses on the surfaces of Earth

plate tectonics

the process involved in the movement of large plates on Earth's crust

mid-ocean ridge

the continuous chain of volcanic submarine mountains that extends around Earth.

faults

a crack in the Earth's crust usually formed when pieces of crust move past each other

trench

a narrow deep depression in the sea floor

magnetic anamolies

magnetic bands in the sea floor that run parallel to the mid-ocean ridge

rifts

a crack in the earth's crust formed as pieces of the crust separate

sea-floor spreading

the process by which new sea floor is formed as it moves away from spreading centers in mid ocean ridges

tectonic plates

regions of Earth's lithosphere which move together over the asthenosphere. there are approx. 20 total plates.

subduction

The downward movement of a plate into the mantle that occurs in trenches, which are also known as subduction zones

shear boundary

the boundary between two plates that move past each

other on the earth's surface.

lithogenous sediment

sediment that is derived from the breakdown, or weathering, of rocks

weathering

the physical and chemical breakdown of rocks

biogenous sediment

sediment that is made up of the skeletons and shells of marine organisms. also see calcareous and siliceous ooze

world ocean

a concept that is used to indicate that all oceans on Earth are interconnected

continental margin

The edge of a continent; the zone between a continent and the deep-sea floor. also see active and passive continental margins.

continental shelf

the shallow, gently sloping section of the continental margin that extends from the shore to the point where the slope gets steeper

continental slope

steeper seaward section of the continental margin

continental rise

the gently sloping area at the base of the continental slope

submarine canyon

A narrow, deep depression in the continental shelf formed by the erosion of rivers or glaciers before the shelf was submerged.

shelf break

The section of the continental shelf where the slope

abruptly becomes steeper, usually at a depth of 120-200

m

active margin

A continental margin that is colliding with another plate and as a result is geologically active

passive continental margin

A continental margin that is located at the "trailing edge" of a continent and as a result shows little geological activity

abyssal plain

the nearly flat region of the deep-sea floor

seamount

a submarine volcano in the abyssal plain

hydrothermal vents

a deep-sea hot spring where heated seawater forces its way up through the crust

sulfide

one of the minerals that is abundant in the hot water that seeps through hydrothermal vents

black smokers

a chimney like accumulation of mineral deposits that is found at hydrothermal vents (mainly iron)

hot spot

An area where magma from deep within the mantle melts through the crust above it (hawaii is on top of a hot spot --> helped form hawaii)

pangea

A supercontinent containing all of Earth's land that existed about 225 million years ago.

Lithosphere

solid outer layer part of earth made of crustal plates

Asthenosphere

part of upper mantle that is more liquid and flows

1. Name Earth's interior layers and their properties. Which classification method (chemical or physical) is more useful in explaining plate tectonics?

1. Core- mostly iron, more than 1,000000 times pressure of surface, over 4000 Celcius, made up of solid inner core and liquid outer core, swirling of liquid produces the magnetic field.

2. mantle- semi-liquid region between crust and core, very hot --> near the melting point of rocks

3. crust- outermost layer, extremely thin, made up of rock giving it rigid attributes.

physical classification easily explains the movement and idea of plate tectonics because they reside in the lithosphere which moves about the asthenosphere, both of which are distinguished on how easily the rock flows

2. Describe the differences between oceanic and continental crusts. What geological and/or chemical processes determine these differences?

oceanic - made up of basalt, darker color, more dense, thinner, younger, rich in iron/magnesium, ocean/seafloor

continental - made up of granite, lighter color, less dense, thicker, old, rich in sodium/calcium/aluminum, land/terrestrial

3. Explain Alfred Wegener theory of continental drift. Why did geologists have such strong objections to Wegener's ideas when he proposed them in 1912?

Alfred's theory is that all continents had all been joined in a supercontinent, bit his ideas were not accepted because he did not have evidence that were the continents were actually moving.

4. What is the accepted theory that explains why the continents and oceans are positioned the way we see them now compared to Pangea?

Plate tectonics and the continental drift are the accepted phenomena that involves the entire surface of our earth and its movements. It also explains why the continents and oceans are where we see them now, compared to Pangea.

5. Describe the mechanism that powers the movement of lithosphere plates. How does the principle of density stratification influence the plate tectonic process?

The mechanism that powers the movement of lithospheric plates is known as subduction. Subduction is known as the downward movement of a plate into the mantle that occurs in trenches, which is also known as subduction zones. For example, the continental block is less dense than the oceanic plate and floats on top, when an ocean plate collides with a continent, it is always the oceanic plate that descends into the mantle. This is known as conitnental drift.

6. What are the three main ways that plates move on the upper mantle? Compare and contrast the three plate movements.

1. Divergent plate separations - magma mountains form, subduction, new/destroyed sphere

2. Convergent/subduction plate collisions - trenches and volcanoes, oceanic plates down, mountains ranges

3. Shear boundaries - slide past each other, immense friction, earthquakes

7. What biological evidence supports plate tectonics theory?

Microbes live on and in the seafloor, inhabiting deep layers of sediment and tiny fissures in the rocks of the crust; living evidence can be studied to at least 10 km deep in the seafloor. This supports the plate tectonic theory because microbes contribute to the formation of rock, which can be traced between the organism and terrestrial location of the rock.

8. What geological evidence can you cite to support the theory of plate tectonics? What questions remain unanswered?

Mid ocean ridges are a form of geological evidence for plate tectonics. Islands, trenches and rock formations are all also part of geological evidence.

9. Describe the differences in the continental margins between those that are active and those that are passive. Where on our coastlines would these likely occur and why?

An active margin is an area with plate boundaries and sites of more intense geological activity, including earthquakes, volcanoes and trenches. It has steep, rocky shorelines, narrow continental shelves and steep slopes with no continental rise. It occurs on the west coast.

A passive margin has no plate boundaries and is relatively inactive. They are characterized by flat, wide, coastal plains, shelves, and gradual sloping. There is a continental rise at the end of the slope. It occurs on the east and gulf coast.

10. Imagine a tectonic plate moving westward. What geological effects would you expect to see on its Western edge? Eastern edge?

Western edge → active margin

Little to no shelf, steep slope, trench (no rise)

Easter edge → passive margin

Wide shelf, gentle slope,continental rise.

11. How does plate tectonics explain the formation of island chains, like those we see in Hawaii?

In order to form island chains, tectonic plates shift and move about the crust of the earth, forming ridges, volcanoes, and trenches that have turned into island chains, like the Hawaiian islands.

12. What creates hydrothermal vents? Why was it such an amazing discovery for scientist in the late '70's? What makes them so unique in terms of an ecosystem?

Hydrothermal vents, deep-sea hot springs where heated seawater forces its way up through the crust; were such an amazing discovery because of their rarity and wonder; create unexpected marine life