Inside the Earth Composition What it is made

Inside the Earth

Composition (What it is made of) • Crust- solid • Mantle- semi-solid • Core – Outer- liquid – Inner- solid

Physical Structure of the Earth (5 Layers) • Lithosphere-solid rigid outer layer (crust) • Asthenosphere- solid plastic like rock that flows slowly (like hot asphalt) • Mesosphere- middle layersolid • Not shown • Outer Core- liquid layer • Inner Core- solid, very dense

What is the Lithosphere? • Rigid, part of the upper portion of mantle and the crust • Broken into tectonic plates • and 100 km thick • Less dense than the material below it so it “floats” on the asthenosphere

What is the Asthenoshere? • The plastic layer of solid rock beneath the lithosphere that has so much heat and pressure the rocks can flow like a liquid • The plates of the lithosphere float on the asthenosphere because it is more dense than lithosphere • The asthenosphere is located about 62 miles beneath the surface of the earth. It has not yet been seen by humans.

ASTHENOSPHERE • Lies right beneath the lithosphere • Layer of rock that is under heat and pressure so it flows like a liquid • They can break apart • More dense than the lithosphere

The Crust • Outer layer • Thinnest layer compared to others • Under oceanic is the thinnest sections of crust • 5 -100 km thick solid • Granite and basalt • 2 types of crust – Oceanic – Continental

2 Types of Plates • Ocean plates - plates below the oceans • Continental plates - plates below the continents

Crust • Oceanic • Continental • very dense, • made of iron (Fe) & magnesium (Mg) and igneous (basalt), • thinner than continental, • more dense than continental • Oceanic crust is also younger* • Layer of Igneous, sedimentary & metamorphic rocks • Form the continents and continental shelves • 25 -70 km thick • less dense, • made of granite • Makes up 1% Earth’s volume

Plate Tectonics

Tectonic Plates • Earth’s crust is broken into about 19 pieces • These plates move on top of the asthenosphere

What is Plate Tectonics • The Earth’s crust and upper mantle are broken into sections called plates • Plates move around on top of the mantle like rafts

Causes of Plate Tectonics

Convection Currents • Hot magma in the Earth moves toward the surface, cools, then sinks again. • Creating convection currents beneath the plates that cause the plates to move.

Questions. . . • What causes plates to move? • How is a convection current formed?

Plate Boundaries

Types • Divergent – Rifting • Convergent – Sub-duction • Transform Fault Boundaries – (Sliding)

Divergent Boundaries • Boundary between two plates that are moving apart or rifting • RIFTING causes SEAFLOOR SPREADING http: //www. pbs. org/wgbh/aso/tryit/tectonics/divergent. html

Divergent Plate Movement: Seafloor Spreading • the movement of two oceanic plates away from each other (at a divergent plate boundary), which results in the formation of new oceanic crust (from magma that comes from within the Earth's mantle) along a a mid-ocean ridge. • Ocean floor spreading was first suggested by Harry Hess and Robert Dietz in the 1960's.

Features of Divergent Boundaries • Mid-ocean ridges • rift valleys • fissure volcanoes

Divergent Boundary • Real Life Example: Mid-Atlantic Ridge • Mid-Atlantic Ridge runs through Atlantic Ocean from Arctic Ocean to an area off the southern tip of South America.

Convergent Boundaries • Boundaries between two plates that are colliding • There are 3 types…

Type 1 • Ocean plate colliding with a less dense continental plate • Subduction Zone: where the less dense plate slides over the more dense plate • VOLCANOES occur at subduction zones

Subduction • Subduction may be defined as the process by which one plate of the earth’s surface shifts so that it moves sideways and beneath a plate located underneath it in the earth’s mantle. http: //www. pbs. org/wgbh/aso/tryit/tectonics/convergent. html

Type 2 • Ocean plate colliding with another ocean plate • The less dense plate slides over the more dense plate creating a subduction zone called a TRENCH

• Two Oceanic Plates - When two oceanic plates collide, one may be pushed under the other and magma from the mantle rises, forming volcanoes in the vicinity

• Two Oceanic Plates - When two oceanic plates collide, one may be pushed under the other and magma from the mantle rises, forming volcanoes in the vicinity

Andes Mountains, South America

Aleutian Islands, Alaska

Type 3 • A continental plate colliding with another continental plate • Have Collision Zones: –a place where folded and thrust faulted mountains form.

• Two Continental Plates - When two continental plates collide, mountain ranges are created as the colliding crust is compressed and pushed upwards.

Transform Fault Boundaries • Boundary between two plates that are sliding past each other • EARTHQUAKES along faults

• When two plates move sideways against each other (at a transform plate boundary), there is a tremendous amount of friction which makes the movement jerky. • The plates slip, then stick as the friction and pressure build up to incredible levels. When the pressure is released suddenly, and the plates suddenly jerk apart, this is an earthquake.

San Andreas Fault, CA

Questions. . . • What are the types of boundaries? • What direction do plates go for each? • Which boundary has a subduction zone…what occurs at a subduction zone?

Pangea. Theory of Continental Drift In the 1800 s, Alfred Wegner developed the Theory of Continental Drift. • He used the following evidence: – Fossils – Climate – Geography

Alfred Wegener Alfred Lothar Wegener, (born November 1, 1880, Berlin, Germany —died November 1930, Greenland), German meteorologist and geophysicist who formulated the first complete statement of the continental drift hypothesis.

• Like certain other scientists before him, Wegener became impressed with the similarity in the coastlines of eastern South America and western Africa and speculated that those lands had once been joined together. • the idea that in the late Paleozoic Era (about 250 million years ago) all the present-day continents had formed a single large mass, or supercontinent, which had subsequently broken apart. Wegener called this ancient continent Pangaea.

Wegener Hypothesis • Wegener proposed that Pangaea’s portions had slowly moved thousands of miles apart over long periods of geologic time. • His term for this movement was die Verschiebung der Kontinente (“continental displacement”), which gave rise to the term continental drift.

Gondwana & Laurasia • He envisioned a single great landmass, Pangaea. Gondwana made up the southern half of this supercontinent. Laurasia made up the northern half of Pangea.

• Gondwana was assembled by continental collisions in the Late Precambrian (about 1 billion to 542 million years ago). Gondwana then collided with North America, Europe, and Siberia to form the supercontinent of Pangea.

Evidence to Back it up • he was able to point to many closely related fossil organisms and similar rock strata that occurred on widely separated continents, particularly those found in both the Americas and in Africa. • By 1930 his theory had been rejected by most geologists, and it sank into obscurity for the next few decades, only to be resurrected as part of theory of plate tectonics during the 1960 s.

• With the mapping of the ocean floor in the late 1940’s, a change of thought began and in the 1960 s it changed when theory of plate tectonics demonstrated that the ocean basins are not permanent global features (sea floor spreading) and vindicated Wegener’s hypothesis of continental drift.

• Seafloor spreading provided a way to explain the movement of continents as the seafloor spreads along the a mid-Atlantic ridge. • The continents bordering the Atlantic Ocean, for example, are believed to be moving away from the Mid-Atlantic Ridge at a rate of 1– 2 cm (0. 4– 0. 8 inch) per year, thus increasing the breadth of the ocean basin by twice that amount.

seafloor spreading in three ocean basins • Patterns of seafloor spreading in the Pacific (left), Arctic (center), and Atlantic oceans (right) showing the relative age of oceanic crust. The youngest regions are colored red, whereas the oldest regions are colored blue.