The Changing Face of the Planet. Earth’s Interior Information gathered about the Earth’s...
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Transcript of The Changing Face of the Planet. Earth’s Interior Information gathered about the Earth’s...
The Changing Face of the Planet
Earth’s InteriorInformation gathered about the Earth’s interior
comes from direct evidence from rock samples
and indirect evidence from seismic waves Rocks from inside the Earth, as well as those ejected during
volcanic eruptions, give geologists clues about Earth’s interior
Earthquakes produce shock waves that travel through the Earth Changes occur in the movement of seismic waves due to
differences in the structure and makeup of the Earth’s interior Scientist have determined what the interior looks like by
monitoring the path and speed of seismic waves
The Earth’s Interior The four layers of
the Earth are the crust, mantle, inner core and outer core
These layers vary greatly in size, composition, temperature, and pressure
The Earth’s Crust The crust is the Earth’s outermost layer Made up of three types of solid rock Thickness varies with type
Oceanic crust (makes up the ocean floor) Less than 10 Km thick Consists mostly of basalt
Continental crust (makes up the landmasses) Average thickness of about 32 Km Made mostly of granite
The Earth’s Mantle Earth’s mantle is made up of rock that is very hot, but solid Divided into layers based on the physical characteristics
of those layers Extends to a depth of about 3000 Km below the surface Contains about 80% of the volume of the Earth and 68%
of its mass Made mostly of the elements silicon, oxygen, iron, and
magnesium Density increases with depth
Divisions of the Earth’s Mantle Mohorovicic discontinuity (Moho)- Boundary
separating the crust from the mantle Lithosphere-
Topmost solid part of the Earth Composed of the crust and part of the upper mantle Broken into large sections called plates
Asthenosphere- Located directly beneath the lithosphere A hot weak zone, capable of gradual flow Rock in this portion of the mantle can flow like a thick liquid (Has plasticity)
Lower mantle- Zone of solid rock, located directly beneath the asthenosphere, and extends to the core
The Earth’s Core The Earth’s core is
subdivided into two layers, and inner and outer core
Both layers are composed mostly of the metals iron and nickel
The Outer and Inner Cores
Outer Core- Layer of the molten metal surrounding the inner core High temperatures keep the iron and nickel in the
outer core molten
Inner Core- Dense ball of solid metal found at the Earth’s center Intense pressure causes the particles of iron and
nickel to remain solid The inner core rotates within the outer core
The Core & Earth’s Magnetic Field Scientists think that convection currents in the liquid outer core create Earth’s magnetic field
The magnetic field helps protect our planet from the Sun’s solar winds
The Earth’s Changing Interior It is believed that the Earth was not originally layered, the
divisions we see today formed slowly over time Shortly after the Earth was formed, the decay of radioactive
elements, along with heat released by colliding particles, produced melting in the planet’s interior
Melting allowed the heavier elements (iron & nickel) to sink toward the center, while lighter, rocky components floated upward
Still occurs today on a smaller scale
Plate Tectonics
Theory which links the concepts of Continental Drift and Sea-floor Spreading to explain how the Earth has evolved over time
Helps to explain the formation, movements, collisions, and destruction of Earth’s outer layers
Helps people understand the geologic past and predict its future
Evidence for Plate Tectonics
Continental Drift
Location of volcanoes,
earthquake belts and mountains
Sea-floor Spreading
Paleomagnetism
Continental Drift Proposed in 1910 by
Alfred Wegener States that the continents
were once joined together as a super-continent called Pangaea and have since drifted apart
Since Wegener could not explain why the continents would move, his theory was originally rejected
Evidence for Continental Drift Shape of the continents Similar fossil deposits on
continents thought to have been joined
Rock formations that end at the edges of continents
Glacial deposits (evidence of past climates)
Distinctive rock types
Location of the world’s volcano, earthquake belts, and mountain ranges
Most volcanoes, earthquakes, and mountain ranges are found along plate boundaries (places where one plate moves relative to another)
Produced by stresses that build up along the boundaries As stresses become too great, fractures form and earthquakes occur Fractures allow magma from the asthenosphere to reach the surface, forming volcanoes Bending and folding of the Earth’s crust can create mountain ranges
Sea-floor Spreading Sea-floor spreading- Process in which old
ocean floor is pushed away from a mid-ocean ridge by the formation of new ocean floor As the ocean floor spreads, landmasses on
either side move apart Occurs at divergent boundaries (also called
spreading centers) Younger rocks are found closer to the spreading
center The further you go from the spreading center, the
older the rocks become The same pattern of rocks are found on both sides
of the center
Paleomagnetism Paleomagnetism- Study of the
alignment of magnetic particles in ancient rocks
Provides proof for sea-floor spreading and a means of determining how the continents have moved
When magma cools, grains of iron line up with the magnetic pole (like little compasses)
Polarity reversals occur in parallel bands on opposite sides of the mid-ocean ridges
During the past 4 million years, the magnetic poles have reversed themselves 9 times
Theory of Plate Tectonics States that the topmost solid
part of the Earth is divided into rigid plates that move resulting in earthquakes, volcanoes, mountains, and the redistribution of landmasses
Lithospheric plates are made of a thin layer of crust above a thick layer of rigid mantle rock
Usually contain both oceanic and continental crust
Seven major plates, each named after its surface features
Plates move at different speeds and in different directions
Earth’s Tectonic Plates
Plate BoundariesThere are three basic types of plate boundaries
Divergent- moving apart Convergent- moving together Transform fault- sliding past each other
Divergent Boundaries Plates move apart (diverge) Also called spreading
centers or constructive boundaries
New rocks are formed as older rocks are pushed aside (Lithosphere is created)
Examples: Mid-Atlantic Ridge, East Pacific Rise, and the Great Rift Valley in Africa
Convergent Boundaries Occur where two
plates move towards each other
Also called destructive
boundaries Lithosphere is
destroyed There are three types
Types of Convergent BoundariesConvergent boundary where two continental plates collide
Forms a single larger continent (India & Asia)
Causes the lithosphere at the boundary to be pushed up, forming a mountain range
Ex.: Himalayas, Urals, & Appalachian Mtns.
Types of Convergent BoundariesConvergent boundary where two oceanic plates collide
One plate subducts (goes under) the other plate Also called a subduction zone Forms a chain of volcanic islands on the overriding plate
and a deep sea trench where the plates meet Ex.: The Mariana Islands and the Mariana Trench are formed where the Pacific Plate subducts under the Philippine Plate
Types of Convergent BoundariesConvergent boundary where an oceanic and a continental plate collides
The oceanic plate subducts under the continental plate Forms a chain of volcanic mountains on the continental
plate and a deep sea trench along the edge of the continent Ex.: Along the west coast of South America, the Nazca Plate subducts under the South American Plate, forming the Andes Mtns. And the Peru-Chile Trench
Transform Fault Boundaries Also known as strike-slip or sliding boundaries Plates grind together as they try to slip past each other horizontally
causing stress to build up Earthquakes occur when the stress is released Examples:
The San Andreas Fault in California, is a result of the North American Plate and the Pacific Plate trying to slide past each other Transform fault boundaries connect portions of the mid-ocean ridge system that are moving at different rates
Why the Plates Move Convection currents within the asthenosphere are
thought to be the driving force behind plate movement Convection current- the movement of material caused
by differences in temperature Hot magma rises to the surface, pushing the older rocks
aside and driving the plates apart (occurs at divergent boundaries)
Cooler, denser currents sink back into the mantle, pushing the plates together (occurs at convergent boundaries)