Plate Tectonics andEarth Structure

Lab 4

Concepts Internal Structure of the Earth

3 components (core, mantle, crust) Seismic tomography

Plate Tectonics Theory Evidence of Continental Drift

Plate Movement Convergence Divergence Transform

Hot Spots

Internal Structure3 main components

Core Solid inner & liquid

outer

Mantle Thick layer of liquid hot

magma Upper mantle & portion

of crust = lithosphere

Crust Oceanic (high density)

& continental (low density)

Internal StructureHow do we know what’s inside the Earth?

Seismic tomography Seismic waves (from earthquakes or underground tests) pass

through the earth and give us an idea of the types of materials that make up the composition

Also, the waves help estimate how thick each layer is.

Plate TectonicsFact or Fiction?

Theory: Earth’s crust is composed of numerous plates, which move due to convection processes in the mantle.

Idea developed in early 1900s, not taken seriously until 1960s. Alfred Wegener proposed the idea of “continental drift” in 1912.

Evidence of continental drift1. Convection Model (explains how plates move around)

2. “Puzzle”-like fit of continents3. Fossil records4. Geologic & Glacial records5. Coal records

Plate TectonicsEvidence of Continental Drift: Convection Model Earth’s core is hot, so heated

magma (near the core) rises up to be closer to the crust, where it can be cooled.

Cooled magma then sinks back to the core.

Constant rotation of magma makes plates move.

The ways in which plates move depend on the direction of the rotation.

Tectonic PlatesEvidence of Continental Drift: “Puzzle”-like Fit of Continents 200 million years ago: Pangaea (“all Earth”)

Earliest landmass formed on Earth. Was a mash-up of all the continents we know today.

Tectonic PlatesEvidence of Continental Drift: Fossil Records

Example: Matching fossil records of reptiles have been found in Africa and South America

Continents were so close to each other (or even joined) that animal life could easily travel to and from them.

Similar fossil records for vegetation found.

Tectonic PlatesEvidence of Continental Drift: Geologic & Glacial Records Similar rock strata

across continents Southwest Africa

matches up with southeast South America, etc.

Evidence of glaciation in areas that are not necessarily glaciated anymore

e.g., Australia

Tectonic PlatesEvidence of Continental Drift: Coal Records

Coal formation Wet and warm climates. Millions of years for

biological material (e.g., plant and animal life) to break down and form coal.

Coal reserve found under ice cap of Antarctica.

Present in many areas of Russia and northern China, as well as northern US and Canada.

Plate Movement

3 types of movement: Divergent, Convergent, and Transform

Plate MovementDivergent Movement

Plates move away from each other, often at mid-oceanic ridges.

Result = trench with mountains to each side.

Red Sea and Great Rift Valley, Africa

Plate MovementDivergent Movement

Plate MovementConvergent Movement, version 1

Plates of the same composition (oceanic vs. oceanic or continental vs. continental) move towards each other.

Result = mountain chain.

Indian and Eurasian plates come together. Form the Himalayas.

Plate MovementConvergent Movement, version 2 Occurs when a heavier oceanic plate comes into contact

with a lighter continental plate. The continental plate is more buoyant, and will rise above the oceanic plate.

The oceanic plate is “subducted” under the continental one. Result = volcanic mountain chain.

The heavier Nazca plate subducts under the lighter South American plate.Forms Andes Mountains.

Plate MovementTransform Movement

Plates slip past each other (parallel motion). Often, the force created by the parallel motion is what sets

off earthquakes.

Pacific plate moves NW, North American plate moves SE. San Andreas fault, CA.

Hot Spots Caused by a mantle plume

A narrow stream of magma rises up from the mantle and breaks through the crust.

Does not necessarily occur on plate boundaries. Example: in middle of ocean Hawai’i Example: in middle of continent Yellowstone

Hot spots are stationary It is the plates moving over them

that creates a series of volcanicformations

Movement away from the hot spotindicates older landforms (furtheraway from active hot spot, theolder it is).

Notice that they are not necessarily on plate boundaries!Hot spots can happen anywhere.

Hot SpotsWhere are they located?

x

“X” marks the current location of the Hawai’ian hot spot. It is creating anew landform, “Lo’ihi”, which is still 3,200 feet below the water surface.

Hot SpotsHawai’i: X marks the [active hot] spot