Layers of the Earth & Ocean Basins Origin & Structure

Ch.2 The Sea Floor

I. Layers of the Earth

I. Layers of the Earth

A. Crust1. This is the layer that

we live on2. The thickness ranges

from five miles under the oceanic crust (made of basalt) to 25 miles under the continental crust (made of granite)

3. Thinnest layer of the earth

I. Layers of the Earth

B. Mantle1. This layer is semi-

liquid

2. Consists of magnesium, iron, & silicon

3. It is ~3000 km wide.

4. More solid closer to the Earth’s surface

I. Layers of the Earth

C. Outer Core1. Consists of liquid due

to the high temperatures

2. It is 2100 km wide

3. This layer consists of nickel & iron

I. Layers of the Earth

D. Inner Core1. This layer is solid.

a. Solid is due to the high pressure exerted on it from the outside layers

2. Consists of the metals nickel & iron

3. Its temperature is 6,000o C

4. Its width is 2,100 km

II. Origin & Structure of Ocean Basins

A. Continental Drift1. First noticed in 1620

by Sir Francis Bacon

2. In 1912 Alfred Wegner proposed all the continents were joined into one supercontinent called “Pangaea”a. Not widely accepted

because no mechanism is proposed

II. Origin & Structure of Ocean Basins

B. Plate Tectonics1. Continents drift as part of

a process that involves the entire Earth’s surface

II. Origin & Structure of Ocean Basins

B. Plate Tectonics2. Mid-ocean ridge system,

a continuous system of submarine volcanoes that encircles the world.

3. Deep depressions in the sea floor, called trenches

II. Origin & Structure of Ocean Basins

C. Mid-Ocean Ridge Significance1. Glomar Challenger, in 1968, began to collect sea floor core

samples

2. Sea floor is very young near mid-ocean ridge crest, & it gets older the further away you get

II. Origin & Structure of Ocean Basins

II. Origin & Structure of Ocean Basins

C. Mid-Ocean Ridge Significance3. Earth’s magnetic field

has reversed in the past (magnetic anomalies)

II. Origin & Structure of Ocean Basins

D. Creation of Sea Floor1. Huge pieces of crust that

separate at the mid-ocean ridge, creating cracks called rifts

2. Hot mantle pushes up through the rifts , cools, solidifies, and form new sea floor

3. Called sea floor spreading & explains the magnetic anomalies