Plate Tectonics and Geology

Genesis of EarthEarth is 4.6 billion years old. Same age as all other planets and the sun.

Earth formation. Nebular hypothesis. Diffuse cloud of matter

rotating in space, formed a disk shaped body, which later formed into sun and planets. Planets are cooled and condensed gases that surrounded the sun.

Core Development Earth was a homogeneous planet immediately after

formation But then, a profound reorganization as Earth initially

heated up due to collision with other rocky bodies heat of compression Radioactive decay of elements

Earth heated up such that much of the interior melted causing dense elements like iron and nickel to sink to the core lighter elements like silicon and aluminum float to the crust Resulted in a stratified Earth - core, mantle, crust

Distribution of Elements More than 100 elements in entire Earth, but

99% of Earth's mass is made up of only 8 elements

Whole Earth: Fe>O>Si>Mg>Ni>S>Ca>Al (others constitute < 1%)

Earth's crust O>Si>Al>Fe>Mg>Ca>K>Na (other constitute <1%)

Composition of Earth’s CrustComposition of Earth’s CrustComposition of Earth’s CrustComposition of Earth’s CrustEarth’s CrustEarth’s Crust

Oxygen 46.6%Oxygen 46.6%

Silicon 27.7%Silicon 27.7%

All others 1.5%All others 1.5%

Magnesium 2.1%Magnesium 2.1%

Potassium 2.6%Potassium 2.6%

Sodium 2.8%Sodium 2.8%

Calcium 3.6%Calcium 3.6%

Iron 5.0%Iron 5.0%

Aluminum 8.1%Aluminum 8.1%

Fig. 10.4, p. 213

Layers of the Earth

Crust The surface of the

Earth is a very thin layer made of rocks, minerals and clay

We live on the crust of the earth

crust

Layers of the Earth

Mantle- Upper and Lower The mantle is the

biggest part of the earth; the magma is rich in iron and magnesium

Convection occurs here and is thought to drive plate tectonics

mantle

crust

Layers of the Earthcrust

mantle

Outer core

•Outer CoreOuter Core•The outer core The outer core consists of molten consists of molten iron and magmairon and magma•The outer core The outer core rotates giving the rotates giving the Earth a magnetic Earth a magnetic fieldfield

Layers of the Earth Inner Core

The inner core is made of solid iron

The closest model of the inner core we have is an iron nickel meteorite

The inner core is under extreme pressure

crust

mantle

Outer core

Inner Core

How do we know about the layers of the Earth?

To date, humans have never drilled through the crust of the Earth.

Scientists study where waves from earthquakes end up around the globe.

The waves move differently through different densities of material.

GEOLOGIC PROCESSES

Spreading centerCollision between

two continentsOcean trench

Plate movement

Subduction zone

Oceanic crust

Continental crust

Continental crust

Material cools as it reaches

the outer mantle

Cold dense material falls back through

mantle

Hot material

rising through

the mantle

Mantle convection

cell

Two plates move towards each other. One is subducted back into the mantle on a falling convection current.

Mantle

Hot outer core Inner

core

Plate movementTe

cton

ic

plat

e

Oceanic tectonic

plate

Oceanic tectonic plate

Oceanic crust

The Earth’s Major Tectonic PlatesEURASIAN PLATEEURASIAN PLATE

NORTH NORTH AMERICAN AMERICAN PLATEPLATE

ANATOLIAN ANATOLIAN PLATEPLATE

JUAN DE JUAN DE FUCA PLATEFUCA PLATE

CHINA CHINA SUBPLATESUBPLATE

CARIBBEAN CARIBBEAN PLATEPLATE

PHILIPPINE PHILIPPINE PLATEPLATE

ARABIAN ARABIAN PLATEPLATEAFRICAN AFRICAN

PLATEPLATEPACIFIC PACIFIC PLATEPLATE SOUTH SOUTH

AMERICAN AMERICAN PLATEPLATENAZCA NAZCA

PLATEPLATEINDIA-INDIA-

AUSTRALIAN AUSTRALIAN PLATEPLATE

SOMALIAN SOMALIAN SUBPLATESUBPLATE

ANTARCTIC PLATEANTARCTIC PLATE

Divergent plate boundaries

Convergent plate boundaries

Transform faults

The Earth’s Major Tectonic PlatesThe Earth’s Major Tectonic Plates

Hawaiian Island Hot Spot

How the hotspot works

History of Continental Drift Hypothesis 1596 Abraham Ortelius: fit of South American & African

coasts 1620 Francis Bacon: noted same fit 1782 Benjamin Franklin: suggested that crust of Earth

"floated" on fluid interior (crust broken and disordered by movement of fluids)

1885 Edward Suess Similarities between Late Paleozoic plant fossils of Africa, India,

South America, Australia & Antarctica Carboniferous glaciers on Africa, S. America, Australia, Inda Southern supercontinent of Gondwana Gondwana named after province in India where there was glacial and

plant evidence (Glosopteris flora) Landbridges, which sank beneath the sea, connected present continent

Continental movement not a new idea Wegener developed hypothesis of "continental drift”. Proposed "continental drift" - published "Origin of

Continents and Oceans" in 1915 Pangaea ("all land") existed about 200 Ma Showed breakup in series of maps Few supporters - mostly European and African geologists Ridiculed by American geologists Can't "sail" continents through oceans (granitic continents

too weak to move through stronger basaltic crust No mechanism to explain movement (Wegener's tidal

forces => too weak) Land bridges the answer to explain fossils