Unit 4 The Restless Earth How do we

Unit 4 The Restless Earth

How do we know about the Earth’s Interior? n. Seismic waves: vibrations that travel through the Earth n. Changes in the speed and direction of seismic waves determine the locations and properties of the Earth’s interior

The Layers of the Earth

Layers of the Earth n. The three main layers of the Earth are: Crust Mantle Core (Outer and Inner)

Crust n. Thin, solid outermost layer n. Two types: Oceanic and Continental

Mantle n. Layer between the crust and the core n. Makes up almost 2/3 of the Earth’s mass

Core n. The central part of the Earth below the mantle n. Composed mainly of iron and nickel n. Outer: dense liquid n. Inner: rigid solid

The Earth as a magnet… Scientists hypothesize that motions within the core and the spinning Earth produce electric currents

Structural Zones of the Earth n. The structural zones of the Earth are: n. Lithosphere n. Asthenosphere n. Mesosphere

Lithosphere nsolid, outer part that consists of the crust and the rigid upper part of the mantle

Asthenosphere nbeneath the lithosphere and due to enormous heat and pressure the solid rock has the ability to flow, tectonic plate movement happens here n. Plasticity: the ability of rock to flow

Mesosphere n“middle sphere”, strong part of the lower mantle between asthenosphere and the outer core

Think!!! The world as a puzzle?

Theory of Plate Tectonics � Revolutionized geologists' understanding of continents, ocean basins, mountains, and earth history � Literally, plates moving, colliding, pulling apart, and creating features

Alfred Wegener (1880 -1930) German geologist and meteorologist 1915 he proposes the idea of continental drift Continental drift: states that the continents once formed a single landmass, broke up, and drifted to their present locations

Continental Drift � States that parts of the Earth's crust slowly drift atop a liquid base (asthenosphere) � Map coastlines, fossil record, climatic plant life and rock formations support theories of continental drift and plate tectonics.

200 million years ago

Pangaea • means “all earth” • simply put, all the continents were once connected

Today

The Break-Up � Two large distinct land masses � Northern portion: Laurasia � Southern Portion: Gondwanaland

Laurasia �Northern portion: consisting of modern day North America, Europe, and Asia

Gondwanaland �Southern portion: consisting of modern day South America, Africa, Antarctica, Australia

Then versus Now Vs.

Panthalassa � � "All seas“ Defined as the super-ocean that existed on Earth durin the time of the super-continent Pangaea

Fossil Evidence: Mesosaurus �Four-legged �Elongated head and snout with nostrils near its eyes �Flattened tail used for swimming �One of the first reptiles �Fossils have been found in South Africa and South America

Glossopteris � Means “tongue”, because the leaves were tongue shaped � Fossils are found throughout India, South America, southern Africa, Australia, and Antarctica � Wide distribution of this fossil

Rock Formations � Ages and types of rocks in coastal regions matched up

Plate Boundaries �Convergent (collide) �Divergent (divide) �Transform (slide by)

Convergent

Subduction Zone Oceanic and Continental � Masses of the spreading oceanic crust bend downward into the continental crust

Magma �Liquid rock produced under Earth’s surface

Two Types of Magma Mafic: Hot, quiet, fluid like eruptions Mainly oceanic volcanoes, dark in color, rich in magnesium and iron Forms pahoehoe lava (rope-like)

Mt. Kilauea

Two Types of Magma Felsic: Cooler, Stickier, Violent eruptions Continental Volcanoes, light in color, rich in silicates Forms blockier lava

Volcanism �Any activity that includes the movement of magma toward or onto the Earth’s surface

Lava � Magma that flows onto the Earth’s surface, the rock that forms when lava cools and solidifies

Volcano � An opening (vent or fissure) in the Earth’s surface through which magma and gases are expelled

Types of Eruptions Viscosity: or resistance to flow of magma affects the force at which a volcano will erupt Which is more viscous felsic or mafic: Felsic

Divergent (Where new crust is formed)

Seafloor Spreading � molten rock (magma) oozes up from the Earth's interior along the mid-oceanic ridges, creating new seafloor that spreads away from the active ridge crest and, eventually, sinks into the deep oceanic trenches

Mantle Convection Think density!: Temperature Differences

Hot Spot Volcano Hot, solid rock rises to the hot spot from great depths Rock begins to melt, forming magma Magma rises through the Pacific Plate to supply the active volcanoes � The older islands were once located above the stationary hot spot but were carried away as the Pacific Plate drifted to the northwest. � � �

Transform (Where two plates slide against each other. ) � two plates move against each other, building up tension � tension is released in a sudden and often violent jerk � sudden jerk creates an earthquake � San Andreas Fault is the most famous transform boundary in the world. To the west of the fault is the Pacific plate, which is moving northwest. To the east is the North American Plate, which is moving southeast.

Earthquakes � movement or trembling of the ground that is caused by a sudden release of energy when rocks a long a fault move, the result of stress

Focus and Epicenter �Focus: location in the earth where earthquake starts �Epicenter: point on Earth’s surface directly above the focus

Differences of Foci Shallow focus: usually more damage, vibrations (energy) reach surface Deep focus: vibrations (energy) dissipate before reaching surface

2004 Indian Ocean Tsunami killed 250, 000 People

Seismic Waves rocks release of energy in the form of vibrations � � Think of dropping a stone in a pond.

Two Types of Waves “Body Waves and Surface Waves” Body travel: travel through the medium the bulk of an object Surface: travel on the surface (outer layer) duh!

Body Waves P waves: (fastest) “Primary”, first to be detected, travel through solids, liquids, and gases S waves: (second fastest) Secondary travel only through solids, side to side

Surface Waves “Rayleigh and Love” Rayleigh: like waves of the ocean, up and down rolling motion Love: like S waves

Recording Earthquakes Seismograph: An instrument that records vibrations in the ground

Earthquakes Magnitude � The measure of the strength of an earthquake (measuring the amount of ground movement, commonly called the Richter Scale) � Recorded in numerical value--- the higher the number, the greater the earthquakes magnitude � Magnitudes of less than 2. 5 usually are not felt by people.